Australian Biological Resources Study

Algae of Australia Glossary

Compiled by John M. Huisman & Timothy J. Entwisle

This glossary contains terms likely to be used in volumes of the Algae of Australia. References used in its compilation are given at the end of the chapter. Where possible, the definitions conform with those in the Flora of Australia and Fungi of Australia, but some have meanings peculiar to algae. Specialised terms will be included in the relevant volumes.



abaxial: of the side or surface of an organ, facing away from the main axis; cf. adaxial.

abscission: the normal shedding from a plant of an aged organ.

accessory pigment: a pigment that absorbs light energy and transfers it to chlorophyll for use in photosynthesis.

accessory: additional to the normal branches or structures.

acentric mitosis: mitosis in which no centrioles are present at the spindle poles.

acicular: needle-shaped and stiff.

acritarch: a hollow, organic microfossil, often bearing spines; the systematic position of many acritarchs is uncertain or unknown.

acroblastic: in Sphacelariales, when branches originate from small, lenticular segments of the apical cell.

acronema: a fine, hair-like projection from the end of a flagellum, containing the central pair of microtubules of the axoneme.

acropetal: developing in sequence from the base towards the apex; cf. basipetal.

actin filaments: intracellular filaments of protein c. 8 nm wide, each consisting of a tight helix of actin monomers, all with the same orientation.

actinomorphic: symmetrical about more than one vertical plane.

actinopod: ray-shaped pseudopodium.

acuminate: tapering gradually to a sharp point.

acute: with a pointed apex or a narrow axil.

adaxial: of the side or surface of an organ, facing towards the axis; cf. abaxial.

adelphoparasite: a parasite that is closely related to its host (in the same tribe or family); cf. alloparasite.

adherent: closely attached or associated.

adjoined: of filaments when joined together, weakly or tightly.

adnate: fused to an organ of a different type and not protruding freely.

adventitious: of a branch or filament, arising after the primary morphological pattern is established, accessory.

aegagropila: a ball-like mass of filaments.

aerophytic: living on the surface of rocks, leaves, stems etc., although sometimes covered by a thin film of water; an alternative term is subaerial.

agar: of Rhodophyta, especially Gelidiales and Gracilariales, a phycocolloid (a sulphated polysaccharide) occurring in the cell walls, and apparently the plesiomorphic polysaccharide condition in the Rhodophyta.

air canal: an elongate, intercellular space.

air bladder: a gas-filled vesicle serving for flotation.

akinete: a single-celled, thick-walled, non-motile spore derived from a vegetative cell.

ala: a wing, e.g. the membranous expanses from the central midrib in some Delesseriaceae; pl. alae.

alga: general term referring to the mostly photosynthetic, unicellular or simply constructed, non-vascular, plant-like organisms that are usually aquatic and reproduce without antheridia and oogonia that are jacketed by sterile cells derived from the reproductivecell primordium; includes a number of divisions, many of which are only remotely related to one another; pl. algae.

algin: the soluble sodium salt of alginic acid.

alginate: the salt form of alginic acid, such as complexed with calcium or barium ions.

alginic acid: a phycocolloid present in the cell walls of Phaeophyceae, consisting of a polysaccharide formed from β-1,4-linked D-mannuronic acid and α-1,4-linked L-guluronic acid units.

algology: an older term for the study of algae, now usually replaced by phycology because, etymologically, ‘algology’ literally means the study of pain.

alloparasite: a parasite that is not closely related taxonomically to its host; cf. adelphoparasite.

alternate: of branches, arising singly on different radii along an axis.

alternate-distichous: a branching pattern in which the lateral branches arise singly from each axial cell (or segment) with a divergence of 180° from the preceding and successive branches, such that they lie in one plane.

alternation of generations: the sequence in a life history in which a haploid, gameteproducing phase alternates with a diploid, meiospore-producing phase.

alveolus: in diatoms, an elongated chamber running from the central part of the valve to the margin, open to the inside and covered by a perforate layer on the outside.

amoeboid: of certain gametes of algae and microalgae, lacking a rigid wall and able to change shape in the manner of an amoeba.

amoeboid organism: without a cell wall but with pseudopodia.

amorphous: without a well-defined shape.

amphiesma: in dinoflagellates, a cellular covering of the vegetative cell, composed of only membranes in naked species, or of thecal plates enclosed in membranes in armoured species.

amphoroid: in the form of an amphora, a vessel with handles (branches) in the upper portion.

amplexicaul: stem-clasping.

ampulla: in Euglenophyta, a flask-shaped invagination at the anterior end of a cell; in Rhodophyta, accessory branch systems, usually tapering distally and occurring in the inner cortex, in which carpogonial branches and/or auxiliary cells are produced; pl. ampullae.

amyloplast: a colourless, starch-forming or starch-storing plastid in certain coenocytic, marine green algae (e.g. Caulerpa and Halimeda).

anaerobic: pertaining to an oxygen-free environment.

anaphase: the stage of mitosis during which the chromatids (daughter chromosomes) begin to move towards the poles of the spindle.

anastomosis/anastomosing: secondary fusing of cells or branches, often forming a reticulate network.

antapical: in coccolithophorids and dinoflagellates, pertaining to the region opposite the apex.

androphore: a branch bearing antheridia.

androsporangium: in Oedogoniales (Chlorophyta), a cell or sporangium producing androspores; pl. androsporangia.

androspore: in Oedogoniales (Chlorophyta), a zoospore that grows into a dwarf male filament.

anisogametes: motile gametes that are morphologically similar but unequal in size and referred to as male (the smaller) and female (the larger).

anisogamy: the fusion of two motile gametes, similar in appearance but of unequal size; = heterogamy; cf. isogamy, physiological anisogamy.

anisokont: the flagella of a cell unequal in length and, usually, of different fine structure.

annual fronds: fronds lasting one year before being shed or degenerating.

annual: a plant completing its life history within one year.

annular: of ridges or ingrowth of walls, ring- or torus-like.

annulus: in diatoms, a ring of costal thickness, often surrounding one or more processes and with a structure different from that of the rest of the valve.

anoxic: without oxygen.

anoxygenic: without the production of oxygen; anoxygenic photosynthesis is carried out by photosynthetic bacteria (other than cyanophytes), which are incapable of splitting water and use other reduced substances (H2S, H2, organic compounds) as electron donors; cf. oxygenic.

ansula: in diatoms (Lithodesmiaceae), the single element of the fringed marginal ridge of Ditylum, shaped as a ribbon longitudinally split in its median part.

antapex: in dinoflagellates, the posterior end of a cell.

antapical half: in dinoflagellates, posterior half of the cell; = hypocone.

antapical plates: in dinoflagellates, those thecal plates covering the antapex of the cell.

antenna pigments: photosynthetic pigments involved in light harvesting (the main accessory pigments and chlorophyll a).

anterior: towards the front or apex of a structure.

anterior invagination: in Euglenophyta, a depression at or near the apex of a cell.

antheridium: a male reproductive organ containing sperm; pl. antheridia.

antherozoid: = spermatozoid.

anticlinal: having filaments or cell divisions perpendicular to the surface of a tissue (usually said of the outer cortex of a thallus).

anticlockwise rotation of the basal bodies: see cruciate 1 o’clock – 7 o’clock type of zoid.

apex: the tip of a thallus or branch, most distant from the point of attachment; in flagellated cells, the end in the direction of movement; pl. apices; adj. apical.

apical axis: in diatoms, the long axis of a bilateral diatom, or the axis between the poles of a frustule.

apical cell: the terminal initial cell of a filament or thallus.

apical depression: a pit at the apex.

apical growth: growth occurring at the apex of an axis or branch.

apical half: in dinoflagellates, the anterior half of the cell; = epicone.

apical margin: the margin of a plant where growth occurs equally from every marginal cell of a lamina or thallus rather than only from a single apical cell.

apical plates: in dinoflagellates, the thecal plates that surround and abut the apex of a cell.

apical plug: in certain genera of Corallinales (Rhodophyta), a muciferous plug situated at the apex of a tetrasporangium or bisporangium and fully or partially blocking a conceptacle pore.

apiculate: terminating abruptly in a straight, distinct point.

aplanosporangium: a sporangium containing a non-motile spore (aplanospore) that germinates directly into a filament, e.g. in Vaucheria (Xanthophyceae); pl. aplanosporangia.

aplanospore: a non-motile spore, otherwise comparable to a zoospore.

apogamy: development of an organism without the normal fusion of gametes.

apomeiotic: forming reproductive cells without meiosis.

apomictic: reproducing by mitosis without karyogamy.

apomorphic: of a character, shared by the group under discussion and its ancestors, often described as derived; cf. autapomorphic, plesiomorphic, synapomorphic.

apoprotein: a protein without its characteristic, prosthetic group.

appendage: a lateral, usually irregularly positioned, short outgrowth on a structure.

appendix: in coccolithophorids, a long, distal growth from the basal plate of the coccolith.

applanate: flattened and closely appressed to the substratum and often lobed.

apposition: thickening of a cell brought about through deposition of wall material onto its inner face.

appressed: pressed closely against a surface (or another organ) but not united with it.

arabinogalactan: a polysaccharide; a polymer of arabinose and galactose.

aragonite: the orthorhombic crystalline form of calcium carbonate.

arborescent: tree-like; in non-geniculate Corallinales (Rhodophyta), a term for a thallus composed of a distinct holdfast and stipe bearing flattened, ribbon-like to fan-shaped branches.

Archaean Era: the oldest geological era of the Earth’s history (2500–4500 Ma), during which life originated and toward the end of which microbes inhabited what was presumably an anoxic ocean.

archeopyle: in dinoflagellates, the area of a cyst where a cell emerges during excystment.

arcuate: arching broadly from base to apex.

areola: in diatoms, a regularly repeated perforation through the valve wall, often marked by more-or-less elaborate multiangular walls or ribs.

areolate: in armoured dinoflagellates, ornamented on thecal plates with deep or shallow depressions, with or without raised sides.

areolith: in coccolithophorids, a dome-shaped holococcolith with an areolate interior composed of thickened ridges of calcite elements.

armoured: in dinoflagellates, having thecal plates of varying thickness and orientation in identifiable tabulation series.

articulated: of a branch or axis, separated into joints or segments by nodes and internodes (as in the articulate coralline algae and the green alga Halimeda).

ascocyst: an enlarged, hyaline or darkly staining cell, usually empty when old.

asexual: reproduction not involving sexual fusion or meiosis, generally via monospores, propagules or fragmentation; progeny genetically identical to the parent plant.

assimilatory: of a filament or cell, containing photosynthetic plastids.

assurgent: inclined upwards (usually curved) from its origin.

aster: in many eukaryotes, a star-shaped array of microtubules radiating from a centriole at the pole of the spindle during mitosis.

astipitate: without a stipe.

asymmetric: differing in form or pattern on each side of a central line.

athecate: = unarmoured.

ATP: adenosine triphosphate, a nucleotide made up of adenosine and three phosphate groups; important in many biochemical reactions because of its role in energy transfer.

attenuate: tapering gradually.

autapomorphic: of a character, derived and unique to a given taxon or monophyletic group; cf. apomorphic, synapomorphic, plesiomorphic.

autocolony: a daughter colony (daughter coenobium) formed within the cell of the parent (mother) colony (mother coenobium) and resembling a miniature version of the parent colony.

autogamous: in sexual reproduction, forming a zygote by the fusion of two haploid nuclei from the same individual.

autolysin: an enzyme that degrades the cell wall of the alga producing it; hence a vegetative autolysin is one that releases asexual spores from a sporangial wall (or vegetative cells from their walls), while a gametic autolysin releases gametes from the gametangial wall.

autosporangium: a cell or sporangium containing autospores; pl. autosporangia.

autospores: non-motile spores produced within a parent cell which develop the same shape as the parent cell at an early stage (before release).

autotrophic: able to synthesise organic compounds from inorganic substances, using light energy (photoautotrophs) or chemical energy (chemoautotrophs).

auxiliary cell (or generative auxiliary cell): in Florideophyceae, a cell that produces the carposporophyte following transfer to it of the zygote nucleus or one of its diploid progeny; cf. nutritive auxiliary cell.

auxiliary mother cell: in Florideophyceae, a cell from which an auxiliary cell is cut off.

auxocaulic: of axes or branches in, for example, Cladostephaceae, growing by enlargement of medullary cells whose number is determined close to the apex.

auxospore: in diatoms, a special cell that expands and in which a much enlarged but normal cell is formed, thus compensating for the diminution in cell size that occurred during a preceding series of vegetative cell divisions; an auxospore is often also a zygote.

auxotrophic: of photosynthetic organisms, requiring a minor supply of organic substances such as vitamins.

awn: a sharp, bristle-like appendage.

axenic culture: a culture of an organism in isolation, free from all other kinds of organisms, including bacteria.

axial: pertaining to the axis or central core of a branch.

axial filament: the central filament or element of a multiaxial core of a thallus or its branch.

axial/axile chloroplast: a chloroplast lying centrally within a cell along its longitudinal axis.

axil: the angle between the axis and a lateral branch or organ.

axile: situated in the axil of an organ.

axillary: arising on, in or from an axil.

axis: of habit, a stem or branch; of structure, the central filament (i.e. uniaxial) or filaments (i.e. multiaxial); pl. axes.

axoneme: the cylindrical arrangement of microtubules, with nine doublets around the periphery and two single microtubules at the centre; characteristic of flagella in eukaryotes.

axopodium: a thin, straight pseudopodium supported by microtubules.

axosome: in certain Haptophyta, a hat-like plug in the transition zone between the flagellum and the basal body.



band or segment: in diatoms, a single element of the girdle.

bar: in coccolithophorids, a bridge.

barren basal body: a fully formed basal body (having once given rise to a flagellum in an earlier developmental stage) without flagella.

barbel: a posteriorly directed spine or a short branch, as in the head of a spear.

basal body: the basal section of the flagellum, lying within the cell and consisting of a short cylinder of nine triplets of microtubules; characteristic of flagella in eukaryotes.

basal cells: cells near the point of attachment to the substratum.

basal siliceous layer: in diatoms, the layer that forms the basic structure of the various components of the frustule.

base plate scale: in coccolithophorids, the organic basal plate of a coccolith upon which the calcified elements are deposited.

basipetal: developing in sequence from the apex towards the base, e.g. of a thallus; the opposite to acropetal.

basipetal growth: growing towards the base.

benthic: attached to, resting on, or associated with the substratum of an aquatic habitat.

benthos: collectively, the organisms that live at the bottom of aquatic habitats.

biconvex: convex on both sides, like a magnifying lens.

bicuspid: with two points or spines.

bifid: divided into two for about half the length.

biflagellate: with two flagella.

bifurcate: divided into two branches of about equal length.

bilabiate process: in diatoms (Lithodesmiaceae), a process consisting of an external tube, sometimes reduced to a low ring (visible under light microscopy), and an internal part with a stalk and a trapezoid end piece closed at the tip but open at each of the two slanting sides by a longitudinal slit (visible under electron microscopy).

bilateral: having branches on two opposing sides of an axis, although not necessarily strictly distichous in arrangement.

bilenticular: of a pyrenoid, surrounded by starch deposited as two lenticular masses.

biliprotein: a chromoprotein in which the prosthetic group is a pigment tightly bound by covalent linkage(s) to its apoprotein.

binary fission: division into two equal or roughly equal progeny.

binomial: a two-word scientific name for an organism, comprising a genus name and a species epithet.

biogenic: produced by or originating from living organisms.

biogeography: the study of the geographic distribution of organisms.

bioluminescence: production of visible light by organisms.

biomass: the total amount of organisms present in a given place at one time.

biotic: pertaining to living organisms.

biphasic: having two phases in the life history.

bipinnate: twice-pinnate, the pinnae themselves being pinnate.

biseriate: arranged in two series or rows.

bisexual: with both sex organs produced within the one structure or thallus; see monoecious.

bisporangium: a sporangium containing two spores; pl. bisporangia.

bispore: a spore from a sporangium bearing two spores.

blade: the broad, flattened part of a thallus, usually surmounting a stipe of some degree.

brackish water: a mixture of freshwater and saltwater; generally with salinity below 25–35%.

bract-cell: in Characeae (Chlorophyta), a one-celled appendage at a branchlet node.

bracteoles: in Characeae (Chlorophyta), a pair of one-celled appendages arising below an oogonium.

branchlet: a smaller lateral branch of a thallus; in Characeae (Chlorophyta), determinate laterals produced in whorls at the nodes of a main axis.

brittlewort: in Characeae (Chlorophyta), an informal name applied to calcareous species.

brown alga: a member of the Phaeophyceae.

bulbil: in certain Characeae (Chlorophyta), a structure, containing starch, formed on a rhizoid.

bulbous: shaped like a bulb, with a swollen, rounded base narrowing to a smaller apex.

bullate: blistered or puckered.

bushy: densely and much-branched.

byssoid: composed of fine threads.



caducous: abscising (separating) soon after appearance.

caespitose: growing in tufts; having many stems from one base.

calathiform: cup-shaped, almost hemispherical.

calcification: a deposition of calcium carbonate in, on, or between the cell walls of a thallus.

calcified: having a deposition of calcium carbonate.

calcified compartment: in genera of Sporolithaceae (Rhodophyta), a structure derived from the wall of a tetrasporangial initial and housing a tetrasporangium.

calcite: the hexagonal crystalline form of calcium carbonate; cf. aragonite.

calicalith: in coccolithophorids, a tube-like coccolith with an open distal end.

callose: an amorphous polysaccharide blocking the older sieve plates of vascular plants and Laminariales (Phaeophyceae).

calyptrolith: in coccolithophorids, a calotte- (cap-) shaped holococcolith having the form of an open cap or basket.

Cambrian: the earliest geological period (505–590 Ma) of the Palaeozoic Era (248–590 Ma) characterised by the occurrence of many conspicuous invertebrate fossils.

canal: in Euglenophyta, a tube-like area connecting the anterior invagination or reservoir to the surrounding medium.

canaliculate: having a channel along the length of an organ or cell.

canal raphe: in the valves of certain pennate diatoms, a tube-like structure running longitudinally along the valve, opening externally via the raphe slit and to the inside by several to many apertures; functions in locomotion.

caneolith: in coccolithophorids, an elliptical, discoid heterococcolith, in a basket-like arrangement with a central area or base of lamellae, and a simple or complex girdle bordered above and below petaloid elements.

cap layer: in Rhodophyta, one or two layers of polysaccharide over each side of the pit-plug between two cells, distinguishable by transmission electron microscopy.

capitate: with an enlargement or rounded head at the upper end.

capitellate: shaped like, or aggregated into, a small head.

capitula cells: in Characeae (Chlorophyta), cells within an antheridium which support the manubrium cells or the antheridial filaments.

capsular: = tetrasporangium.

Carboniferous: a late period (286–360 Ma) of the Palaeozoic Era (248–590 Ma) characterised by the formation of massive deposits of coal.

carboxysome: a polyhedral organelle present in blue-green algal (Cyanophyta) cells, containing the enzyme RuBisCO (responsible for CO2 fixation during the dark reactions of photosynthesis); = polyhedral body.

carotenoids: orange-yellow, isoprenoid polyene pigments containing carbon and hydrogen.

carpogonial branch/filament: a uniseriate branch, two to several cells long, bearing a terminal carpogonium.

carpogonial: of a carpogonium.

carpogonium: in Rhodophyta, the female gamete (oogonium); pl. carpogonia.

carposporangium: in Rhodophyta, a specialised cell of the carposporophyte in which the contents are transformed into a normally diploid carpospore and eventually released, leaving behind the parent sporangial wall; pl. carposporangia.

carpospore: in Rhodophyta, a normally diploid spore produced by a carposporophyte.

carposporophyte: in Rhodophyta, the diploid generation following fertilisation, composed of gonimoblast filaments and carposporangia; it is borne on the female gametophyte and, when mature, it releases carpospores that germinate to produce the tetrasporophyte.

carpotetrasporangium: in Rhodophyta, a carposporangium in which the contents are divided into four carpospores, possibly (but not always) following meiosis.

carrageenan: an extracellular, non-fibrillar component of red algae of the Gigartinales which has gelling properties and is extracted commercially for use in food preparation and industry; a sulfated galactan.

cartilaginous: firm and tough but moderately flexible.

cartwheel structure: a flagellar structure composed of nine tilted triplets connected by radial spokes, at the lower end of the basal body.

catenate: in the form of a chain.

caudate: in coccolithophorids, having a tail; in other algae, having a shaggy, tail-like appearance.

caulerpicin: a toxin produced by Caulerpa (Chlorophyta).

caulescent: becoming stalked.

cauloid: stem-like.

cell: the basic, internally cohesive, structural unit of organisms.

cell equator: the plane in the centre of the cell which coincides with the spindle equator at mitosis and in which a new wall is formed between the daughter cells.

cell fusion: a linkage between cells of two vegetative or reproductive filaments in which portions of the cell walls break down and the protoplasts then apparently fuse; cf. fusion cell.

cell membrane: the outer membrane of a cell; cf. plasmalemma.

cell plate: a flat, plate-like array of vesicles containing cell wall material, which develops during cell division and later gives rise to the new cross-wall when the vesicles fuse.

cellulose: the common, structural carbohydrate of plant cell walls, composed of β-1,4-glucosides, commonly in the form of microfibrils.

cellulose synthase: an enzyme complex bound to the plasmalemma which produces cellulose microfibrils outside the plasmalemma by polymerising glucose present within the cytoplasm.

Cenozoic Era: the geological era from 65 Ma to the present characterised by, among other events, a great diversification of mammals and angiosperms.

central cell: the central cell of the axis, where this is surrounded by several pericentral or periaxial cells.

central nodule: in diatoms, a thickening at the centre of the valve in raphid pennate diatoms, separating the fissures of the raphe.

centric mitosis: mitosis in which pairs of centrioles are present at the spindle poles.

centripetal: developing from the periphery in towards the centre.

centrin: see rhizoplast.

centriole: a cell organelle with the same structure as a basal body; centrioles lie at the poles of the mitotic spindle in many eukaryotes and are apparently involved in the formation of the spindle; cf. microtubule organising centre.

centromere: the structure by which a chromosome is attached to its chromosome microtubule(s) during nuclear division; = kinetochore.

centroplasm: in Cyanophyta, the central, unpigmented part of the cytoplasm.

ceratolith: in coccolithophorids, a horseshoe-shaped coccolith. chambered: internally subdivided or partitioned.

chasmoendolith: a microalga inhabiting a narrow crack or fissure that penetrates from the surface in suitably translucent rocks, e.g. sandstone.

chasmolithic: living within rock fissures.

cheilosporoid: with segments as in Cheilosporum, compressed with two upper (usually acute) lobes.

chemoheterotroph: an organism that must consume organic molecules for both its carbon and energy supplies.

chemokinesis: non-directional movements of motile gametes, triggered by chemicals secreted by gametes of the opposite sex.

chemotaxis: movement in a direction determined by a chemical gradient.

chevron: the form of a broad, inverted V.

chlamydomonine: having the basic structure of a Chlamydomonas cell but without flagella.

chlorophyll: the fat-soluble, photosynthetic green pigment of plants and algae, consisting of closed tetrapyrrols with magnesium.

chloroplast: an organelle bounded by a double membrane containing chlorophyll a and other pigments in thylakoids.

chloroplast endoplasmic reticulum: an extension of the endoplasmic reticulum to enclose the chloroplast, sometimes also connecting with the outer nuclear envelope.

choanoflagellate: a flagellated organism in which a ring-like cluster of rhizopodia forms a collar around the flagellum which acts to filter and trap bacteria.

chromatoplasm: in Cyanophyta, the peripheral cytoplasm of the cell, containing thylakoids and the photosynthetic pigments associated with them.

chromosome microtubules: see spindle.

chrysolaminarin: the storage product of most Chrysophyta, consisting largely of β-1,3-glucopyranoside units.

cicatrigenous branch: in Rhodomelaceae, a branch arising from a scar cell, which is a basal cell of a shed trichoblast; thus, it is indirectly exogenously developed.

ciliates: the informal name for organisms belonging to the protozoan phylum Ciliophora, characterised by numerous cilia, two nuclei, and the presence of a cell mouth.

cilium: = flagellum.

cingulum: in diatoms, a girdle or region of a frustule connecting the two distal valves; in dinoflagellates, a girdle or transverse groove in dinokont-type cells, usually a furrow encircling the cell once or several times.

circadian rhythm: see endogenous rhythm.

circinnate: coiled into a ring, or partially so; like a fern crozier.

circular cingulum: in dinoflagellates, a cingulum that is not displaced and in which the proximal end meets the distal end.

cisterna: a flat vesicle bounded by a plasma membrane (e.g. Golgi cisternae); pl. cisternae.

cladogram: a tree-like diagram expressing a hypothesis about phylogeny and constructed according to the methods of cladistics, in which the branches (clades) closest to each other share the most recently derived traits.

class: a major taxonomic rank, between phylum (division) and order.

clathrate: forming a net or reticulum.

clavate: with the shape of a club, narrow at the base and widening gradually to the apex.

cleavage furrow: a ring-shaped invagination that brings about cell division (cytokinesis).

clockwise rotation of the flagellar basal bodies: see cruciate 1 o’clock – 7 o’clock type of zoids.

clonal culture: a population descended from one individual.

clone: a group of individuals propagated by mitosis from a single ancestral individual.

closed mitosis: mitosis that takes place within an intact nuclear envelope; = intranuclear mitosis.

clumping: the formation of dense clusters of flagellate gametes (zoogametes) of two sexes as a result of adhesion of their flagella, occurring immediately before fusion of the gametes.

cnidocyst: = nematocyst.

coalesce: to unite or merge by growing together.

coated vesicle: a spherical vesicle surrounded by a dark-staining layer of protein called clathrin; formed during endocytosis and exocytosis; cf. endocytosis.

coccoid: spherical or globose in form; non-motile stage of the life history; = coccal.

coccolith: in coccolithophorids, a minute scale on the cell surface of some prymnesiophytes, encrusted with calcium carbonate, usually in the crystalline form of calcite; often abundant as fossil remains in chalk.

coccolith case: in coccolithophorids, a cell covering of coccoliths in which the coccoliths hold together to form an intact shell of scales.

coccolithophorid: a unicellular organism classified within the Haptophyceae (Prymnesiophyceae) that bears variously sculptured calcareous scales (coccoliths) upon its cell surface.

coccolithosome: a small granule, 25 nm in diameter, in the Golgi bodies of coccolithophorids.

coccosphere: in coccolithophorids, a cell covering, not necessarily spherical, of coccoliths.

codiolum phase: in some Chlorophyta, a unicellular, diploid stage in the life history; otherwise known as a zygote.

coenobium: a colony in which the number of cells is fixed at its origin and not increased as the colony ages.

coenocyst: a multinucleate, thick-walled cyst.

coenocytic: with large (usually elongate) multinucleate cells, without cross-walls in vegetative parts.

coherent: remaining attached.

colonial: of an organism, formed by a loose or more-or-less defined aggregation of similar cells.

colony: a well-defined group of individual cells usually with distinct morphology, which can be held together in various ways, e.g. by a common envelope of mucilage.

columella: in Phaeophyceae, the central, conical, cellular mass within the conceptacles of some Fucales, bearing a terminal tuft of trichothallic hairs; in Rhodophyta, a structure formed from a group of persistent but often senescent, sterile cells, arising from the floor of a tetrasporangial/bisporangial conceptacle in some Corallinaceae.

columnar cell: in non-geniculate Corallinales (Rhodophyta), an elongate, vegetative cell in which the end walls (those possessing primary pit connections) are much shorter than the side walls, and cell length is substantially greater (usually 2–4 times) than cell diameter.

community: a distinctive assemblage of organisms, usually in a restricted environment and with one to few dominant species.

compatible strain: a strain that is able to mate with another uninhibited by genetically determined restraints.

compatible: see homothallic and heterothallic.

complanate: flattened or branched in one plane.

compressed: flattened, but not strongly so; with an ovate cross-section.

concavo-convex: concave on one side and convex on the other.

conceptacle primordium: in some Phaeophyceae and Rhodophyceae, a group of initials from which a conceptacle develops.

conceptacles: in certain Phaeophyceae and Corallinales (Rhodophyta), flask-shaped cavities in which reproductive organs are borne.

conchocelis phase: sporophyte phase of Porphyra and Bangia, usually endolithic in calcareous material such as shells.

conchosporangium: in Rhodophyta, a type of enlarged sporangium usually produced in series by the conchocelis phase of several members of the Bangiales; pl. conchosporangia.

conchospore: in Rhodophyta, a spore produced and released singly by a conchosporangium in the conchocelis (sporophyte) phase of Porphyra and Bangia, inhabiting calcareous material.

condriome: the whole complement of mitochondria present in a cell.

confervoid: composed of threads or filaments.

confluent: becoming united to form one entity.

conjugation: generally, the fusion of two gametes of opposite sex; in certain bacteria and the green algal order Zygnemales, the formation of a bridge between two cells during sexual reproduction, the male (donor) cell injecting genetic material into the female (recipient) cell through the bridge.

conjunctor cell: in Rhodophyta, a small cell, cut off from a larger vegetative cell, which subsequently fuses with another large cell, thus transferring a nucleus from one to the other and leaving a secondary pit connection between the progenitor and the recipient cell.

connate: fused to another organ.

connecting band: in diatoms, an element in the middle of the girdle when intercalary bands are present, or any element when no intercalary band is present.

connecting cell: in Rhodophyta, a cell that effects the transfer of the zygote nucleus from the fertilised carpogonium to the auxiliary cell.

connecting filament: in Rhodophyta, a filament through which the zygote nucleus is transferred from the carpogonium (or nearby cell) to the auxiliary cell.

connective: in flagellate cells, a component of the flagellar apparatus consisting of a fibrous band of material that connects the microtubular roots just below the insertion of the flagella.

contiguous: immediately adjacent.

continuous microtubules: = interzonal spindle microtubules.

contractile vacuole: a rhythmically contacting vesicle that expels fluid from the cell; cf. osmoregulation.

convergent evolution: the evolution of similar features in unrelated taxa; that is, characters that look the same but do not have the same evolutionary origin.

converging: getting progressively closer.

convolute: partly inrolled from the margin.

copula: a girdle band of a diatom.

copulation: association and fusion of two flagellate gametes, or of a flagellate male with a non-flagellate female gamete.

coralline algae: red algae of the order Corallinales which deposit calcium carbonate in the form of calcite in the cell walls.

coralloid: resembling a branched coral in form.

core: in non-geniculate Corallinales (Rhodophyta), the region of a monomerous thallus in which filaments or portions of filaments are orientated more-or-less parallel to the thallus surface.

coriaceous: leathery, somewhat tough.

corneous: having a horny texture.

corona: in Acetabularia and related genera (Chlorophyta), a whorl of appendages above and below the whorl of gametangial rays; in Characeae (Chlorophyta), the five (or ten) cells at the upper end of the oogonium; in coccolithophorids, a crown or crown-shaped structure.

cortex: the outer layer of cells or tissue of the thallus, external to the medulla; in Characeae (Chlorophyta), longitudinally arranged cells ensheathing the axial filament that give it a striped appearance.

cortical: pertaining to filaments or cells that make up the cortex.

cortical cytoplasm: the outermost layer of cytoplasm in a cell.

corticated: covered with an outer layer, usually of smaller cells.

corticating: similar to ‘cortical’, but generally referring to filaments or cells that form a secondary cortex over the thallus.

corticolous: living on bark surfaces of higher plants; = epiphloeic.

cosmopolitan: widely distributed throughout the world.

costa: an elongate, central thickening to a branch; a midrib; pl. costae.

costal strip: in choanoflagellates, the tubular silica units making up the costa.

costate: having a costa or midrib.

counter-clockwise (anticlockwise) rotation of the basal bodies: see cruciate 11 o’clock – 5 o’clock type of zoid.

cover cells: in Ceramiales (Rhodophyta), cells cut off in association with tetrasporangia, functioning as superficial, protective covers; in Corallinales (Rhodophyta), the outermost cells of the epithallus of the vegetative plant body.

crenulate: scalloped, with small rounded teeth.

Cretaceous: the last geological period (65–144 Ma) of the Mesozoic Era (65–248 Ma), characterised by the formation of massive deposits of chalk composed primarily of the calcareous scales of coccolithophorid algae.

cribrate: in coccolithophorids, sieve-like, perforated.

cribrilith: in coccolithophorids, a strainer-shaped discolith with a perforated central area and a rim composed of lamellae.

cribrum: in diatoms, a velum perforated by regularly arranged pores which occludes one of the many simple or chambered pores through a diatom frustule.

crisped: curled up with a much and irregularly divided margin.

crista: the invaginations of the inner mitochondrial membrane; pl. cristae.

cross-walls: cell walls perpendicular to the direction of axis growth or cell elongation.

crown cells: = corona.

cruciate 11 o’clock – 5 o’clock type of zoid: a zoid with apically inserted, almost opposite flagella in which (when the zoid is viewed from the anterior end) the basal bodies of the two flagella are slightly displaced anticlockwise; sometimes also in quadriflagellate zoids, but only for two of the four flagella.

cruciate 1 o’clock – 7 o’clock type of zoid: a zoid resembling the cruciate 11 o’clock – 5 o’clock type, but with anticlockwise rotation; sometimes in quadriflagellate zoids, where the basal bodies of two flagella occupy the 1 o’clock – 7 o’clock positions.

cruciate microtubular roots: in Chlorophyta, four microtubular roots that anchor the flagella in the cell and form a cross when seen from the apex of the cell; cf. microtubule, microtubular root.

cruciately divided/cruciate: of tetrasporangia, referring to the pattern of cleavage in which the four spores are produced by successive divisions at right angles (walls appear as a cross); cf. decussate.

crust: a thin, closely adherent, outwardly radiating thallus, pseudoparenchymatous in structure with laterally cohering basal and erect filaments.

crustose: forming a lax or firm crust or layer on the substratum.

cryptoendolith: a microalga inhabiting microscopic pores between rock crystals a few millimetres below the surface of a suitably translucent rock, e.g. sandstone.

cryptostomata: a flask-shaped cavity opening to the surface and containing hairs (e.g. in Fucales, Phaeophyceae).

crystallolith: in coccolithophorids, a disciform holococcolith, consisting of regular rhombohedrons of calcite deposited on the distal surface of an organic scale.

cultured: see laboratory culture.

cuneate: wedge-shaped.

cupulate: cup-shaped.

cupule: a small, cup-like structure.

cuticle: a hyaline, firm, non-fibrillar polysaccharide coating of the cortex.

cyanelle: an intracellular structure presumed to represent a once endosymbiotic blue-green alga.

cyanophycin granule: in Cyanophyta, a granule of proteinaceous reserve material, mostly about 0.5 µm in diameter.

cyrtolith: in coccolithophorids, a heterococcolith with a convex, disc-like shape; cyrtoliths may have various types of centres that protrude distally from the cell.

cyst: a resistant, usually thick-walled cell that later produces reproductive cells; a sac or cavity.

cystocarp: in Rhodophyta, a reproductive structure arising following fertilisation, including the diploid carposporophyte and the sterile, protective pericarp derived from the haploid, female gametophyte.

cytogamy: = plasmogamy.

cytokinesis: a division of cell cytoplasm, usually immediately succeeding division of the nucleus.

cytopharynx: a permanent invagination of the cell surface through which food is taken up and incorporated into food vacuoles.

cytoplasm: the contents of a cell within the plasmalemma.

cytoskeleton: the internal skeleton that maintains cell shape and the proper arrangement of the cell organelles, and also the capacity for cell movement and intracellular transport; composed of microtubules, actin and other filaments, myosin molecules, etc.

cytostome: a permanent, mouth-like organelle present in the cells of certain unicellular protozoa and algae (e.g. Noctiluca), through which food is taken up.



dactyl: in Characeae (Chlorophyta), the ultimate, unbranched portion of a branchlet, composed of one or more cells.

DAPI: 4’,6-diamidino-2-phenylindole, a DNA-specific fluorescent dye used to highlight nuclei.

deciduous: loss of branches, usually seasonally.

decumbent: a growth pattern in which the axes arise from a single basal holdfast but become secondarily attached to the substratum and more-or-less lie parallel to it.

decussate: divided into pairs alternately at right angles; a sporangium with cross-walls in three, rather than two, perpendicular planes.

defined medium: a medium in which the chemical ingredients and their concentrations are known.

dehiscent: opening when mature to release contents.

deltoid: triangular, with approximately equal sides.

dendroid: tree-like, basally stalked and much-branched above.

dentate: with marginal teeth.

denticulate: in dinoflagellates, thecal markings or surface ornamentations consisting of spines having a broad base which taper to a narrow point like a tooth; generally, having minute, marginal teeth.

denuded: left bare following the loss of lateral branches.

depression: in dinoflagellates, a surface ornamentation (pit) on thecal plates.

desmid: a unicellular or filamentous green alga that has conjugation of non-flagellate, amoeboid gametes; a member of the Desmidiales (Zygnemophyceae).

desmoschisis: division of cells in which the parental wall forms part of the wall of the progeny.

desmokont: in dinoflagellates, a dinoflagellate cell type in which two dissimilar flagella emerge from the anterior part of the cell; cf. dinokont.

determinate: having a genotypically determined fixed limit to growth.

determinate lateral: a side branch with limited (determinate) growth.

dextral: see imbrication, dextral.

Devonian: a geological period (360–408 Ma) in the Palaeozoic Era (248–590 Ma).

diagnosis: a short description of a taxon which distinguishes it from similar taxa.

diaphragm: a thin sheet of cells which divides internal spaces.

diatom: a unicellular alga encased in a siliceous shell or frustule; a member of the class Bacillariophyceae.

diatomaceous earth: siliceous deposits made up of the sedimentary buildup of diatom frustules.

dichotomous: in branching, dividing equally into two as a result of a longitudinal division of the apical cell; most of what appears to be dichotomous branching in the algae is pseudodichotomous, where the lower lateral branch or cell develops to be equal in size and comparable in position to the primary branch or cell.

diffuse growth: active cell division in almost any part of the thallus, not localised.

digitate: branched like the fingers of a hand.

dimerous: in non-geniculate Corallinales (Rhodophyta), a type of thallus construction involving two distinct groups of filaments which are produced successively and are oriented more-or-less at right angles to one another; cf. monomerous.

dimorphic: having two forms; in coccolithophorids, a coccolith case bearing two types of coccoliths; cf. heteromorphic.

dinoflagellate: a member of the division Dinophyta (formerly called the Pyrrophyta).

dinokaryon: in dinoflagellates, a type of nucleus in which the chromosomes remain condensed and exhibit a characteristic ‘garland structure’ (helicoidal structure) throughout interphase.

dinokont: in dinoflagellates, a cell type in which two flagella are inserted ventrally; one flagellum is transverse and housed in a cingulum (or girdle), the other is longitudinal and housed in a sulcus (the transverse flagellum provides propulsion and imparts spin, the longitudinal flagellum provides direction); cf. desmokont.

dioecious: having the male and female gametes produced on different individuals.

diplobiontic: having two free-living phases in the life history.

diplohaplontic life history: a life history containing two vegetative phases, one diploid and one haploid: the diploid phase arises through the growth and division of a diploid zygote, itself formed by the fusion of two haploid gametes; the haploid phase develops from a haploid meiospore, produced following meiosis in a cell of the diploid phase.

diploid: having two sets of chromosomes (2n) in each nucleus; the condition of cells following fertilisation and before meiosis. diploidisation: the formation of a diploid cell or thallus by means other than the fusion of gametes.

diplontic: when the diploid phase is the prominent one and the haploid phase consists only of the gametes; not to be confused with diplobiontic (q.v.).

diplophase: the diploid vegetative phase of a life history.

direct life history: reproduction of the same phase of the (potential) life history by means of asexual spores or propagules.

discobolocyst: in Chrysophyceae, minute, discoid structures located just beneath the cell surface which shoot out their contents upon stimulation.

discoid: forming a flattened disc with a rounded outline.

discolith: in coccolithophorids, an ellipsoidal coccolith, usually with a raised margin and a central pattern that is different in its arrangement of elements from that of the margin, opening distally; in some species the margin is very high, forming a vase- or barrelshaped coccolith.

discrete: separate, not aggregated, joined or coalescent.

displaced cingulum: in dinoflagellates, a cingulum in which the distal end is either above (ascending) or below (descending) the proximal end that is always on the left side of the cell.

distal: furthest from the point of attachment.

distichous: having lateral branches on opposing sides of an axis, the thallus lying in one plane.

distromatic: with two layers of cells, giving a cross-section two cells thick.

diurnal rhythm: a cycle based upon a daily periodicity; cf. endogenous rhythm.

dithecate: of coccolithophorids, having a double-layered coccolith case, the distal layer monomorphic, proximal layer dimorphic; coccoliths of both layers different.

divaricate: branching at wide angles.

divergent: of branching, spreading at a moderate angle.

division: a major group of plants or algae, equivalent to ‘phylum’.

DNA-DNA hybridisation: a method of estimating genetic (and hence phylogenetic) relationship by in vitro combination of DNA strands from different organisms.

dominant: an ecological term for a species that is usually most frequent or abundant, often largest, and usually of major influence on the composition of the community.

dormancy: the resting state of an organism in which life processes are slowed down in order for the organism to survive adverse conditions; it occurs particularly in hypnospores and hypnozygotes.

dorsal: pertaining to the upper surface of a dorsiventral thallus.

dorsiventral: with distinct upper and lower surfaces.

drift: detached plants cast up on the shore.

doublet: see axoneme.

dwarf males: see nannandrous.

dynein arms: in the axoneme of a flagellum, protein arms borne by the A-tubule of each peripheral doublet, which ‘walk’ along the B-tubule of the adjacent doublet and thus cause the doublets to slide over one another.

dystrophic waters: the acidic, oligotrophic waters of peaty areas, coloured brown by humic acids.



ebracteate: without a bract.

ecdysis: in dinoflagellates, the process of shedding or casting off the thecal plates or armour whereby one of the internal membranes, the innermost membrane, becomes the new outer membrane.

ecoform: a growth form considered to be environmentally derived; sometimes termed an ecophene.

ecological niche: the particular role of a species in a community of organisms, expressing its place in the network of relationships between all species present.

ecology: the study of organisms in relation to one another and their environment.

ecophene: see ecoform.

ecorticate: without a cortex.

ecostate: without a costa or midrib.

ecosystems: the organisms in a community together with the abiotic factors that influence them.

ectocarpin: in Ectocarpus (Phaeophyceae), a sex hormone produced by female gametes causing cluster formation by the male gametes and their accumulation at the source of the hormone.

ectocarpoid: having a structure which resembles that of Ectocarpus; said of thalli that comprise erect, branched filaments, and of plurilocular sporangia that are siliquose and multiseriate.

ectoparasite: a parasite living on the surface of its host.

ectoplasm: a peripheral layer of cytoplasm in the cells of some eukaryotes (e.g. Characeae) which is relatively rigid and non-granular.

edaphic: of the soil.

egg: a female gamete, lacking flagella.

ejectosome: in Cryptophyta, a minute body lying beneath the cell surface which discharges explosively upon stimulation to release a tightly wound band of material which unrolls during discharge.

elachistoid: forming dense tufts, with distally free filaments, similar to those of Elachista(Phaeophyceae).

element: in coccolithophorids, any of the basic parts of which a coccolith is constructed, discernible by the bounding suture lines; in nomenclature, a single (or more if small) specimen, illustration, or herbarium preparation (sheet, box, packet, jar, microscope slide) used for the purposes of typification.

eleutheroschisis: cellular division in which the walls of the cellular products are entirely new and free from the parental walls; cf. segregative cell division.

elevation: in diatoms, the raised margin of a valve wall, not projecting laterally beyond the valve margin and with much the same structure as the valve.

ellipsoid: a solid of elliptic shape; adj. ellipsoidal.

elliptic: shaped (in two dimensions) like an ellipse, oval with regularly rounded ends.

embryo: a young, multicellular organism derived from the zygote or a spore, before differentiation into the mature organism.

encrusting: crust-like; in non-geniculate Corallinales (Rhodophyta), a term for a thallus that is crustose and flattened or sleeve-like and devoid of protuberant or lamellate branches.

endedaphic: living in soil.

endemism: of a taxon, confined to a particular geographical region; adj. endemic.

endochite: in Fucales (Phaeophyceae), the innermost layer of the oogonium. endocytic: living within a cell.

endocytic: living within a cell.

endocytosis: the uptake of material by a cell through incorporation of the substances into vesicles pinched in from the plasmalemma; special cases are termed phagocytosis, pinocytosis; cf. coated vesicle.

endogene: a process taking place inside the cell.

endogenous: of a branch, developing from within the tissue of the parent axis.

endogenous cyst: in Chrysophyceae and Xanthophyceae, a cyst whose wall is formed within the protoplast of a unicellular alga; = statospore.

endogenous rhythm: cyclic changes or behaviours in an organism maintained by the organism itself, regardless of artificial changes to its external environment (e.g. constant temperature or light); a circadian endogenous rhythm has a 24-hour cycle; cf. diurnal rhythm.

endolithic: living within rock.

endoparasite: a parasite living within the tissue of its host.

endophyte: an organism living within the tissues of a host plant or alga.

endoplasm: cytoplasm that is granular, streams actively, and lies in the interior of the cell surrounded by a thin, peripheral layer of rigid, non-granular ectoplasm (e.g. amoebae).

endoplasmic reticulum (ER): a net-like system of flat and tubular vesicles, bounded by membranes, lying in the cytosplasm; occurs as rough and smooth endoplasmic reticulum.

endospore: the innermost layer of the wall in a thick-walled spore or zygote.

endospores: in Cyanophyta, spores that form following division of the protoplast, enclosed within the parent cell wall.

endosymbiont: an organism that lives within the tissues or among the cells of another organism (the host) without causing disease or other obvious negative consequences, but acts to the mutual benefit of both partners.

endotheca: in coccolithophorids, the proximal layer of coccoliths.

endozoic: living within an animal.

enrichment culture: a laboratory culture to which nutrients have been added to encourage the growth and reproduction of one or more species.

ensiform: shaped like a sword.

entire: having a smooth margin, not dissected or lobed.

entwined: entangled or intermixed.

envelope: a wall-like covering around the cells of unicellular or colonial flagellates as, for example, in Chlamydomonas (Chlorophyta), through which the flagella pass; in coccolithophorids, a continuous outer case or skin covering the scales and coccoliths.

Eocene: a geological epoch (37–58 Ma) early in the Cenozoic Era (65 Ma to the present).

epicingulum: in diatoms, the ring-like side wall of the epitheca.

epicone: = epitheca.

epidaphic: living on the soil surface.

epidermis: the outermost cell layer of a thallus; usage usually restricted to anatomically complex thalli, e.g. in Laminariales and Fucales (Phaeophyceae).

epigenous: growing upon (but necessarily firmly attached to) a substratum.

epilimnion: the upper layer in a freshwater lake, when the lake water is separated into a warmer, less dense upper layer and a colder, deeper layer (the hypolimnion).

epilithic: living on rock.

epipelic: living on mud or sand.

epipelon: periphyton attached to, or associated with, mud or silt.

epiphloeic: = corticolous.

epiphyllous: living on the leaf surface of a higher plant.

epiphyte: an organism living directly on a plant or alga; adj. epiphytic.

epiphyton: periphyton attached to macroalgae or aquatic vascular plants.

epipsammon: periphyton attached to, or associated with, sand.

episome: = epitheca.

epithallial cell: in the Corallinales (Rhodophyta), a cell formed outwardly from a division of a vegetative initial or from an asymmetrical, transverse division of a primigenous cell of a dimerous thallus.

epithallus: see hypothallus.

epitheca: in diatoms, the upper, overlapping part of a frustule; in dinoflagellates, the anterior part of the dinokont-type cell above the cingulum; = epicone or episome.

epivalve: in diatoms, the principal element of the epitheca, covering one end of the cell.

epizoic: living attached to an animal.

ER: see endoplasmic reticulum.

estuary: a body of water usually fed by a river but also with a marine influence.

eukaryotic: with the characteristics of the Eukaryota (with membrane-bound nucleus, mitochondria, ER, Golgi apparatus, 9+2 flagellum structure).

eulittoral: the intertidal zone between the sublittoral and the littoral fringe.

euphotic zone: the upper layer in aquatic systems capable of sustaining photosynthesis, generally considered to extend to the depth penetrated by one percent of the incident surface light.

euryhaline: tolerant of a broad range of salinities.

eurythermic: having a broad range of tolerance and a flattened, optimum temperature curve.

eutrophic: nutrient-rich; cf. mesotrophic, oligotrophic.

eutrophicated waters: waters that have become eutrophic (mostly) through pollution.

evanescent: soon disappearing; lasting only a short time.

excystment: in dinoflagellates, when the hypnozygote matures and is ready to produce a motile cell from the resting cell, a naked meiocyte will emerge from the archeopyle or opening in the wall; the emerging cell will be either flagellated or amoeboid (typically, this cell will undergo meiosis and produce four vegetative haploid (n) cells that are motile).

exochite: in Fucales (Phaeophyceae), the outermost layer of the oogonium.

exocytosis: the secretion of material from a cell, through the fusion of the vesicle containing the material with the plasmalemma; cf. endocytosis.

exogene: a process related to the cell, but taking place outside the cell membrane.

exogenous: originating from the surface of a thallus.

exogenous cyst: in Chrysophyceae and Xanthophyceae, a cyst whose wall is laid down against the outside of the protoplast of a unicellular alga.

exospore: in Cyanophyta, a spore cut off externally by a spore mother cell.

exotheca: in coccolithophorids, the distal layer of coccoliths.

exothecal: in coccolithophorids, from the distal layer. extension growth: growth brought about by elongation of the cells rather than through cell division.

extrusome: a membrane-bound organelle usually confined to the cell surface; mucoid content may be extruded to form threads.

eyespot: see stigma.



facultative gamete: a zoospore that may function as a gamete.

facultative heterotrophy: the ability of photosynthetic organisms to carry on heterotrophic nutrition if the circumstances present themselves.

falcate: shaped like a scythe or sickle.

false branching: a type of branching occurring in some types of filamentous algae (particularly Cyanophyta), where the filaments are surrounded by a mucilage sheath; a filament breaks and then one or both ends grow out laterally from the sheath.

false hairs: tapering, hair–like extensions of filaments, e.g. in the Ectocarpaceae (Phaeophyceae) with almost colourless cells and without a basal meristem; cf. phaeophycean hairs.

family: a taxonomic group between order and genus; family names of algae end in -aceae.

farinose: covered with a white mealiness.

fascicle: a cluster of filaments or branches, with the parts subparallel.

fasciculate: formed of fascicles.

fastigiate: with branchlets clustered, erect and subparallel, but tapering above.

fenestra: an opening, window. Thus, the polar fenestrae are openings in the nuclear envelope at the two poles of the spindle in a closed mitosis; pl. fenestrae.

fertile: bearing sporangia or gametangia.

fertile sheet: the cellular layer or layers lining the inside of the conceptacle from which the reproductive structures are produced.

fertilisation tubule: a minute tubule that connects the uniting gametes of certain flagellate green algae.

fibrous: divided into slender fibres.

fibula: in pennate diatoms with a canal raphe, bridges of silica which lie between the pores connecting the cell lumen with the canal beneath the raphe; pl. fibulae.

filament: a long row of cells attached end to end, usually uniseriate, or less accurately a very elongate and narrow coenocytic cell or part thereof; cf. siphon.

filamentous: in habit, referring to hair-like plants composed of linear series of mostly uncorticated cells, generally not consolidated into a substantial thallus; in morphology(e.g. filamentous medulla or cortex), composed of free filaments, not forming a coherent tissue; cf. parenchymatous, pseudoparenchymatous.

filiform: thread-like, usually several cells thick.

filopodium: a fine, protoplasmic thread protruding from a cell surface; trailing behind a swimming flagellate or anchoring the cell to the substratum; pl. filopodia.

fimbriate: fringed.

first apical plate: in dinoflagellates, the plate in armoured dinokonts which is typically situated directly above the subapical plate.

fissipariety: in diatoms (Lithodesmiaceae), split wall character, i.e. a localised in vivoseparation of the siliceous and diatotepic layers of the cell wall, the diatotepic layer being the acidic layer rich in carbohydrates between the siliceous layer and the plasmalemma.

flabellate: fan-shaped.

flaccid: limp.

flagellar apparatus: the whole complex of flagellar basal bodies, microtubular roots and their associated structures, and rhizoplasts (if any).

flagellar canal: in dinoflagellates, a narrow invagination of the plasmalemma, from the floor of which a flagellum arises; in Chlorophyceae, a canal in the cell envelope through which the flagellum runs and emerges to the exterior.

flagellar pit: a depression in the cell surface from the bottom of which the flagella arise.

flagellar pores: in dinoflagellates, one or two pores through which flagella emerge (all dinoflagellates at some time in their life history have two dissimilar flagella).

flagellar roots: structures composed of microtubules and striated fibres that connect to the bases of flagella inside the cell; function largely unknown but includes controlling the conformation of the flagellar apparatus and anchorage within the cell; cf. microtubular root.

flagellate: bearing one or more flagella.

flagellar swelling: a swelling at the base of the flagellum that often lies appressed to the eyespot; presumed to be involved with light perception; = paraflagellar body; cf. photoreceptor apparatus.

flagellum: a long, cylindrical extension from cells conferring motility on the cell; structurally with nine peripheral doublets and two central microtubular strands; pl. flagella.

flanged: of branches, with slightly projecting, longitudinal ridges.

flared: spread out or broadened above the base.

flexed: a structure that is bent above its point of origin.

flexuose: with numerous twists and bends.

flimmer flagellum: a flagellum with usually two rows of tripartite, tubular hairs along the whole or part of its axis.

flimmer: = mastigoneme.

floridean starch: in Rhodophyta, the reserve polysaccaride, present as granules outside the rhodoplasts, consisting of an α-1,4-linked glucan.

flosculolith: in coccolithophorids, a holococcolith consisting of a distally widening tube with a vaulted roof that partially closes the distal tube opening.

foliaceous: leaf-like.

foliose: bearing leaves or leaf-like structures.

food vacuole: a vacuole into which solid food particles are taken up by phagotrophy and in which they are digested.

foramen: in diatoms, the passage through the constriction at the surface opposite the velum; pl. foramina.

foraminifera: a phylum of protozoans characterised by the possession of a porous, calcareous shell (often resembling a minature snail shell).

forming face: of a Golgi body, the side on which cisternae are assembled through fusion of vesicles derived from the ER or nuclear envelope.

formvar: material for producing very thin films for supporting specimens in the electron microscope.

fossil: the remains or traces of an organism from the geological past, found embedded in rocks or sediments; microfossils are the fossils of microscopic organisms, or the pollen or spores of organisms cf. micropalaeontology.

fountain-type structure: see multiaxial.

fragariolith: in coccolithophorids, a stomatal coccolith of Anthospheaera species with a large distal, single-layered leaf-like process.

fragmentation: vegetative reproduction by disintegration, dispersal of fragments, and subsequent regeneration of thalli.

free-floating: floating at or under the surface of water; not attached.

free-nuclear division: repeated mitosis without intervening cytokineses.

frond: the main part of a thallus above the holdfast.

front: in the sea, a boundary between different water masses.

fructan: a polysaccharide; a polymer of fructose.

frustule: in diatoms, a siliceous shell external to the plasmalemma.

fruticose: generally, shrubby; in non-geniculate Corallinales (Rhodophyta), a term for a thallus with protuberant branches that are themselves usually branched and over 3 mm long.

fruticulose: somewhat shrubby.

fucalean: pertaining to the Fucales (Phaeophyceae) in structure or reproduction.

fucoidan: in Phaeophyceae, a complex, water-soluble, sulphated polysaccharide found in the mucilaginous fraction of the cell walls; composed of the monosaccharide fucose and varying proportions of other monosaccharides.

fucosan: in Phaeophyceae, a substance with tannin–like properties which accumulates in cells; considered to be a by-product of metabolism with a possible role in deterring grazers.

fucosan vesicle: in Phaeophyceae, a small, refractive vesicle in a cell, containing fucosan; = physode.

fucoserraten: in Fucus (Phaeophyceae), an erotactin (sex hormone) produced by the eggs which attracts sperm.

fucoxanthin: in Phaeophyceae, Bacillariophyceae and Haptophyta, the predominant carotenoid pigment of brown algal phaeoplasts.

furcate: forked, divided into two, usually fairly equally, but not strictly dichotomous.

furcellaran: a sulfated polysaccharide wall component with mucilaginous properties produced by the red alga Furcellaria; chemically similar to carrageenan.

fusiform: spindle-shaped, thicker centrally and tapering to both ends.

fusion cell: in Rhodophyta, the enlarged cell produced through the fusion of an auxiliary cell or zygote with one or more adjacent cells, gametophytic, carposporophytic, or both.



galactan: a polysaccharide; a polymer of galactose.

gametangial rays: of the class Dasycladophyceae, radial gametangia.

gametangium: a cell or specialised structure in which gametes are formed; pl. gametangia.

gamete: a haploid, sexual cell; fusion of two haploid gametes produces a diploid zygote.

gametic meiosis: meiosis resulting in direct formation of gametes in a diplontic life history.

gametogenesis: the process by which gametes are formed.

gametophore: a branch bearing one or more gametangia. b the haploid phase (usually multicellular) of the life history which produces gametes.

ganglioid cell: a cell with elongate arms or processes.

gas vacuole: in Cyanophyta, an irregularly shaped, gas-filled structure in the cell, composed of aggregates of closely packed gas vesicles.

gas vesicle: in Cyanophyta, a small, cylindrical structure with proteinaceous walls and filled with gas, which occurs in clusters in the cytoplasm (forming gas vacuoles).

gelatinous: slimy and jelly-like.

generation: one of the phases (gametophyte or sporophyte) in a life history.

generative auxiliary cell: see auxiliary cell, nutritive auxiliary cell.

geniculate: possessing genicula.

geniculum: the uncalcified ‘joint’ region in articulated, coralline red algae and also in the calcareous green alga Halimeda; pl. genicula.

genome: the sum total of the genes contained either in the nucleus or in the nucleoid of an organelle (mitochondria, chloroplasts) in eukaryotes, or in the nucleoid of a prokaryote.

genophore: a gene-containing body.

genus: main taxonomic rank above species and below family; pl. genera.

geotaxis: movement in response to gravity — in the direction of the gravitational force (positive geotaxis) or away from it (negative geotaxis).

girdle: = cingulum.

girdle lamella: a lamella composed of three thylakoids which runs around the periphery of a chloroplast in chlorophyll c-containing organisms, and runs parallel and close to the chloroplast envelope.

girdle view, broad: in diatoms, view of a frustule seen from the broad side; cf. valve view.

girdle view, narrow: in diatoms, view of a frustule from the narrow side; cf. valve view.

glabrous: without hairs.

gland cell: see vesicular cell.

gliding movement: movement of organisms without flagella or pseudopodia when in contact with a substratum.

gliscolith: in coccolithophorids, a holococcolith with a circular to elliptic basal ring, a distal neck of the same diameter as the ring, and a distal, inflated globular section; internally the gliscolith is hollow, the inflated distal part of the coccolith (and sometimes the stalk) being penetrated by pores.

globose: almost spherical; cf. orbicular.

globule: a nearly spherical inclusion in a cell.

glomerate: collected into heads or dense clusters.

glucan: a polysaccharide; a polymer of glucose.

glycoprotein: a protein with carbohydrates attached to it.

Golgi apparatus: a complex of Golgi bodies or the whole complement of Golgi bodies within a cell.

Golgi body: a cell organelle typical of eukaryotes consisting of a stack of flat, disc-like cisternae whose edges are generally slightly to greatly inflated; the cisternae cut off vesicles containing various substances (e.g. wall material).

gonidium: a reproductive cell; in Volvocales (Chlorophyceae), an enlarged cell that gives rise to a daughter colony; pl. gonidia.

gonimoblast: in Rhodophyta, a filament of diploid cells which produces carpospores; developing from the zygote or from an auxiliary cell that has acquired the zygote nucleus or a diploid nucleus derived from the zygote nucleus.

gonimoblast initial: the primordium of the gonimoblast.

gonimocarp: in Rhodophyta, the collective name for the structure formed by a group of gonimoblasts.

gonocyte: in multicellular, parasitic dinoflagellates, a type of cell that undergoes cell division, located in the middle of a colony, with a trophocyte at the anterior end and sporocytes to the posterior end.

gram stain: a stain containing crystal violet and iodine which, following treatment with alcohol, is retained by the walls of gram-positive bacteria but not by those of gramnegative bacteria.

granum: a stack of thylakoids resembling a pile of coins, the membranes of adjacent thylakoids being fused; pl. grana.

green alga: a member of the Chlorophyta.

grid: a circular, thin, finely meshed plate c. 2.5 mm in diameter used to support formvar film in the electron microscope.

gubernaculum: trailing flagellum; cf. tractellum.

gullet: a deep depression at the anterior of the cell in some unicellular flagellates (euglenoids, cryptomonads) from which the flagella arise.

gynandrosporous: in some Oedogoniales, having an androspore develop on the female filament.



habit: the overall morphological form of an organism.

habitat: the environment in which an organism lives.

haematochrome: astaxanthin or 3: 3’ diketo 4: 4’ dihydroxy-β-carotene.

hair: an elongate, uniseriate extension, not or only slightly pigmented, tapering or cylindrical, including false hairs (without a basal meristem) and phaeophycean hairs (with a basal meristem).

hamate: hooked at the tip.

haplobiontic: with a single, free-living phase in the life history, the only diploid phase being the zygote. See haplontic life history.

haplogenotypic sex determination: separation of the different sexes during meiosis, such that the homologous chromosomes with the alleles for ‘maleness’ (+ alleles) are segregated from those for ‘femaleness’ (− alleles); the meiospores inheriting male (+) alleles grow into haploid ‘male’ (+) plants, while those inheriting female (−) alleles grow into haploid ‘female’ (−) plants; 50% of the plants are male and 50% female as a result of this process.

haploid: having a single set (n) of chromosomes; the condition of cells following meiosis and before fertilisation.

haplontic life history: a life history containing only one vegetative phase, which is haploid; the diploid phase consists only of a zygote cell; see haplobiontic.

haplophase: the haploid, vegetative phase of a life history.

haplostichous: of thallus construction, having free or consolidated filaments but lacking intercalary, longitudinal cell divisions.

hapteroid: of attached structures, somewhat like a hapteron.

hapteron: a branched, usually relatively robust, attachment organ, usually along a prostrate or recumbent axis; pl. haptera; cf. holdfast.

haptonema: in Haptophyta, a thread-like appendage arising near the flagella, containing six or seven simple microtubules (arranged in section in a crescent) and a fold of endoplasmic reticulum.

haustorium: a specialised cell that is presumed to absorb nutrients from a host organism; pl. haustoria.

hecatonemoid: of a thallus, resembling Hecatonema in being discoid and distromatic.

helicoid placolith/helicolith: in coccolithophorids, a placolith with helical shape.

helladolith: in coccolithophorids, a holococcolith with a double-layered, leaf-like appendage.

hemi-atmophytic: living in a thin film of water covering bare rock or moss.

hemiblastic: in Sphacelariales (Phaeophyceae), of lateral branches from cells below the apex of the main axis with the lateral as broad as the whole length of the parent segment; cf. holoblastic.

hemiparasite: an organism that is partially parasitic but largely independent and photosynthetic.

hermaphroditic: producing both male and female gametes on the same individual; cf. monoecious.

herbivore: an organism that feeds on photosynthetic organisms; = primary consumer.

heteroblasty: the formation of two morphologically different germinating patterns from spores liberated from a single sporangium.

heterococcolith: in coccolithophorids, a coccolith built of elements of different forms, the crystals being basically rhombohedral but continuing to grow so that their characteristic face becomes somewhat modified; cf. holococcolith.

heterocyst: in Cyanophyta, site of nitrogen-fixation; a cell distinguished from normal vegetative cells by its glassy, often yellowish, non-granular appearance and thick wall, often thickened even further internally where it adjoins other cells.

heterodynamic: of flagellar movement, flagella of the same cell acting in different ways (e.g. one pulling, the other trailing).

heterogamy: = anisogamy.

heterokaryotic thallus: a thallus containing genetically different haploid nuclei, e.g. with nuclei bearing the male genetic factor and nuclei bearing the female genetic factor; rare in algae but common in fungi; cf. homokaryotic thallus.

heterokont zoids: zoids with two flagella that behave differently and have a different structure; of zoids in the Heterokontophyta, where each cell bears a forwardly directed, pleuronematic flagellum and a backwardly directed, smooth flagellum.

heteromorphic: of two different forms, usually pertaining to a life history in which the gametophyte and sporophyte phases are morphologically dissimilar; cf. dimorphic.

heteroplastidic: in Bryopsidophyceae, having two types of plastids in the cells: chloroplasts and amyloplasts; cf. homoplastidic.

heterothallic: a single, haploid organism having two kinds of gametes that are incompatible with each other (i.e. the organism is self-incompatible).

heterotrichous: having a thallus composed of distinct prostrate and erect portions.

heterotrophic: gaining nutrients through the uptake of organic substances produced by other organisms.

heterotypic synonyms: in nomenclature, synonyms based on different nomenclatural types.

hirsute: hairy.

histones: structural proteins present in eukaryote chromosomes, containing very high proportions of positively charged amino acids (lysine and arginine) that bind tightly to DNA and are responsible for the coiling and packing of the chromosomal DNA; = histoproteins or nucleohistones.

histoproteins: = histones.

holdfast: a basal attachment organ; cf. hapteron.

holoblastic: in Sphacelaria (Phaeophyceae), having a branching pattern in which the branch primordium originates from the entire segment of an apical cell; cf. hemiblastic.

holocarpic: having the whole contents of a vegetative thallus divide into reproductive cells (e.g. Caulerpa).

holococcolith: in coccolithophorids, a coccolith formed solely by calcite microcrystals held together by an organic matrix; the calcium carbonate is deposited as uniform, rhombohedral or hexagonal crystals showing little modification; cf. heterococcolith.

hologamy: the process in which two whole organisms fuse with each other during sexual reproduction.

holoplanktonic: organisms that spend their entire existence as free-floating individuals.

holotype: the single specimen or element on which an author bases the description and naming of a new taxon.

homodynamic: of flagellar movement, flagella of a single cell which are active more-or-less synchronously.

homokaryotic thallus: a thallus containing genetically identical, haploid nuclei; cf. heterokaryotic thallus.

homologous: similar as a result of common evolutionary descent.

homology: a fundamental similarity of traits reflecting common evolutionary descent.

homoplastidic: in Bryopsidophyceae, possessing chloroplasts but not amyloplasts; cf. heteroplastidic.

homothallic: a single haploid organism having two kinds of gametes which are compatible with each other (i.e. the organism is self-compatible).

homotypic synonym: in nomenclature, a name based on the same nomenclatural type as a previously published name.

hormogonium: in Cyanophyta, a multicellular fragment of a filament formed by necrosis of cells at either end and which serves in vegetative reproduction, often capable of active gliding movements.

horns: in armoured dinoflagellates, prominent apical or antapical extensions of the cytoplasm covered by thecal plates.

host: an organism on or in which another organism grows.

hyaline: of cells or filaments, unpigmented.

hyaline band: in diatoms, an element of girdle with no perforations.

hygroscopic: readily absorbing or losing water and thence changing form.

hypacroblastic: origin of laterals from cells below the apical cell from either the full length of the parent cell (hemiblastic) or from a subdivision of the parent cell (meriblastic).

hypersaline: with a salinity above that of normal sea water.

hypha: elongate, slender cells or filaments derived laterally from medullary cells (in larger brown algae); pl. hyphae.

hypnospore: a resting spore; a thick-walled resting stage that can germinate only after an obligatory period of dormancy.

hypnozygote: a thick-walled, resting zygote that germinates after an obligatory period of dormancy.

hypocingulum: in diatoms, the ring-like side wall of the hypotheca.

hypocone: = hypotheca.

hypogenous cell: a cell lying beneath another structure; in Ceramiales (Rhodophyta), the cell below the fertile axial cell.

hypogynous cell: in Rhodophyta, a cell immediately below the female carpogonium.

hypolimnion: see epilimnion.

hypolithic: living on the lower surface of rocks.

hyporheic: the subsurface region of a stream or river which exchanges water with the surface.

hyposome: = hypotheca.

hypothallus: in Rhodophyta, the basal layer of a crust-like thallus or part of a thallus composed of one or more layers of densely packed, fused filaments (the primigenous filaments); these filaments grow parallel to the substratum through division of apical cells, which together form the margin of the crust. Other densely packed, fused filaments arch upwards (the postigenous filaments) forming the perithallus of the crust, which grows in thickness through division of distally intercalary perithallus cells, these in turn being covered by one or more layers of non-dividing epithallus cells.

hypotheca: in diatoms, the lower (younger) half of a silica shell (frustule); in dinoflagellates, the posterior or antapical part of a dinokont-type cell below the cingulum; = hypocone or hyposome.

hypotonic: of a cell, with the osmotic pressure higher than in the surrounding medium, which may result in the cells swelling and rupturing.

hypovalve: in diatoms, the principal element of the hypotheca, covering one end of the cell.

hystrichosphere: a spherical or ellipsoidal microfossil with spiny projections (often the fossil cyst of a species of dinoflagellate).



idioandrosporous: in Oedogoniales (Chlorophyta), having the androspore produced by a special filament (other than the female).

imbricate: overlapping, like tiles on a roof.

imbrication, dextral: in coccolithophorids, in distal view each element overlaps the one to the right when viewed from the centre of the coccolith.

imbrication pattern: in coccolithophorids, the particular pattern of overlapping.

imbrication, sinistral: in coccolithophorids, in distal view each element overlaps the one to the left when viewed from the centre of the coccolith.

incised: cut or divided deeply and sharply, often irregularly.

inclination, clockwise: in coccolithophorids, a suture inclined to the right; cf. suture.

inclination, counterclockwise: in coccolithophorids, a suture inclined to the left; cf. suture.

incompatible gamete: see heterothallic.

incompatible strain: a strain that is unable to mate with another, usually because of genetically determined traits.

indeterminate: capable of unlimited growth.

indeterminate lateral: a side branch with unlimited growth, often exhibiting the same structure and mode of growth as the main axis; = long shoot.

inducing factor: a chemical produced in certain algae which effects the sexual maturation of immature individuals.

indusium: a covering over a sorus, derived from the outer thallus membrane; pl. indusia.

inferior: below another organ.

inflexed: bent inwardly.

infrageneric: taxonomic ranks below the level of genus.

infraspecific: taxonomic ranks below the level of species; cf. intraspecific.

initial, initial cell: generally, the first cell of a plant or tissue, from which the plant or tissue ultimately develops; in diatoms, the first cell of a new vegetative phase, produced within the auxospore and often having a unique morphology.

inoculum: a group of living cells or organisms used to begin a laboratory culture of algae after transfer to a new culture medium, or acting to initiate a new population in nature.

intercalary: between two points (usually cells); refers to the position of structures or meristems that occur between normal, vegetative cells rather than at the tips of axes or filaments.

intercalary band: in diatoms, an element of a frustule in the girdle region, located next to the valves.

intercalary growth: growth in the middle of a tissue or filament, not at the tip.

intercalary plates: in armoured species of dinoflagellates, plates between the precingular and the apical series (anterior intercalaries), or plates between the postcingular and the antapical series (posterior intercalaries).

intercalation: the positioning of cells or structures in-between pre-existing cells or structures.

intercellular: lying between cells.

intergeneric: between genera.

intergeniculum: the calcified region in articulated, coralline red algae and the green alga Halimeda between the uncalcified joints; pl. intergenicula.

intergrade: an intermediate form between two species or varieties.

internode: the part of an axis between two nodes.

interphase: the period in a nuclear cycle between two nuclear divisions.

interspecific: between species.

interstice: a space between parts of a thallus.

interstria: in diatoms, a non-perforate, siliceous strip between two striae.

intertidal: occurring between extreme low tide and extreme high tide and, therefore, exposed at some stage; see eulittoral.

interzonal spindle microtubule: a continuous spindle microtubule that extends from one pole of the mitotic spindle to the other; during anaphase it appears to increase in length, thus separating the chromatids, but in fact separation seems to be achieved more by the microtubules sliding over one another.

intracellular: within a cell.

intrageneric: see intraspecific.

intranuclear mitosis: = closed mitosis.

intraspecific: within a species; often used to describe variation within a species (intraspecific variation); by analogy, also intrageneric etc.; cf. infraspecific.

introrsely: growing inwardly.

intussusception: the growth of something by deposition of new material within an existing structure.

invagination: an infolded hollow or cavity.

inverted repeats: two identical sections of the circular chloroplast genome containing the genes for chloroplast ribosomal RNA which are transcribed in opposite directions (i.e. inverted).

involucre/involucral filaments: in Rhodophyta, sterile filaments that envelop reproductive structures, typically arising from the carpogonial branch or adjacent filaments and enveloping the carpogonium and/or gonimoblast, but also found enveloping other reproductive structures.

involute: rolled inwards from the edges.

iridescent: sparkling, rainbow-hued.

isobilateral: capable of being divided into two similar halves in one plane only.

isodiametric: with approximately equal length and breadth.

isogametes: morphologically identical (usually motile) gametes, even though they may belong to different sexes (usually designated + and −).

isogamy: copulation (fusion) of isogametes; cf. anisogamy, physiological anisogamy.

isokont: having two equal, similarly structured flagella.

isomorphic: having gametophyte and sporophyte phases of similar (or identical) morphology and size.

isotype: a duplicate specimen from the same original collection as the holotype.

isthmus: in order Desmidiales (Zygnemophyceae), a constriction between two semicells.



janioid: branched as in Jania (Rhodophyta), i.e. subdichotomously with terete branches.

Jurassic: a geological period (144–213 Ma) in the middle of the Mesozoic Era (65–248 Ma).



karyogamy: the fusion of the nuclei of two gametes; cf. plasmogamy.

keel: a prominent, longitudinally running ridge.

kelp: a member of the Laminariales (Phaeophyceae); also bull kelp for Durvillaea species.

kinetochore: = centromere.

kinetome: the complement of centrioles, basal bodies and flagella present in a cell.



L/B: length divided by breadth; or as ratio length to breadth (L:B).

L/D: length divided by diameter; or as ratio length to diameter (L:D).

L/W: length divided by width; or as ratio length to width (L:W).

labiate process: in diatoms, a tubular structure in the valve of a frustule opening externally by a simple pore or extended outwards and opening internally via a slit resembling a mouth flanked by two lips.

laboratory culture, cultured: grown under artificial conditions.

lacerate: torn or irregularly cleft.

laciniate: slashed, torn or divided into narrow, usually tapering lobes.

lacrymuloid: tear-shaped.

lacunae: cavities within a structure; see lumen.

lagoon: a shallow lake of salt or brackish water separated from the sea.

lamella: in a chloroplast, a stack of thylakoids which extends along the whole length of the chloroplast.

lamellate branch: in non-geniculate Corallinales (Rhodophyta), a more-or-less flattened or curved branch that usually has a dorsiventral, internal organisation.

lamellate: composed of thin layers or plates of tissue.

lamina: the flat blade or flattened, upper part of stalked algae.

laminarin: a soluble, storage product of brown algae; a polysaccharide composed of β-l,3-linked glucans with some β-l,6-linkages forming a branching polymer.

laminate: flattened to form a lamina.

laminolith: in coccolithophorids, a laminated, disc-shaped holococcolith, with or without perforations.

lanceolate: lance-shaped; long and narrow, tapering to both ends, especially to the apex.

lateral: directed sideways, as in branches arising from a main axis.

lax: loose and soft; not rigid.

layered: in non-geniculate Corallinales (Rhodophyta), a term for a thallus that consists of several to many lamellate branches arranged in horizontal layers.

leaf: occasionally used in algae for a flattened structure superficially resembling the leaf of a green plant, as, for example, in Sargassum (Phaeophyceae).

lectotype: a specimen selected, in the absence of a holotype, as the nomenclatural reference point of a taxon.

lenticular: lens-shaped, with both sides convex.

lepidolith: in coccolithophorids, a thin, ellipsoidal, disc-shaped coccolith.

leptocaulous: with the secondary segments of branches not increasing in size (Sphacelariaceae).

leucoplast: a colourless plastid that contains no thylakoids or only vestigial ones and which is homologous to a chloroplast; its function is the synthesis of reserve polysaccharide.

levels of organisation: different levels of complexity of thallus structure. The following levels, supposedly representing increasingly derived states, can be distinguished: the monadoid level (unicellular flagellates); the colonial monadoid level (colonial flagellates); the amoeboid level; the capsal (encapsuled-tetrasporal or palmelloid) level; the coccal (coccoid) level; the trichal (filamentous) level; the thallose (thalloid) level; and the siphonous level.

life cycle: a now outdated term for life history, abandoned because of its misleading implication of programmed regularity that does not accurately describe many organisms.

life history: the sum of an organism’s morphological, cytological and reproductive phases.

lignin: a complex carbohydrate deposited in the cell walls of woody tissue.

ligulate: strap- or tongue-shaped.

lineage: in morphology, a line or row of cells, usually indicative of their origin; in phylogeny, the ancestry of an individual or taxon.

linear: narrow, with parallel sides and several times longer than broad.

lipid: the ester of a fatty acid, insoluble in water.

lipopolysaccharide: a molecule consisting of lipid linked to polysaccharide; important constituents of the cell walls of blue-green algae (Cyanophyta).

list: in dinoflagellates, a membranous extension of an armoured dinoflagellate; wing, flange.

lithophyte: a plant growing on rock; see epilithic.

littoral fringe: the zone above the eulittoral, usually dominated by littorinid snails; the lower part of the supralittoral.

littoral zone: loosely used for the main part of the intertidal zone, now largely replaced by eulittoral.

locule: in diatoms, a chamber within the frustule having a constricted opening on one side and a velum on the opposite side; generally = loculus.

loculate areola, locule: in diatoms, an areola markedly constricted at one surface of the valve; cf. poroid areola.

loculus: a chamber of a reproductive organ; pl. loculi.

long shoot: = indeterminate lateral.

long-day response: a response to the perception of long periods of light per day (e.g. longer than a critical daylength of, for instance, 12 h); in fact, it is the length of the dark period that is critical, and a flash of light during the dark will counter the effect.

longitudinal flagellum: see longitudinal furrow.

longitudinal furrow: in dinoflagellates, a sulcus or furrow in a cell surface, running from the anterior end or the centre of the cell towards the posterior, in which the longitudinal flagellum lies.

longitudinal section: a thallus section cut along the axis of one or a parallel group of filaments.

longitudinal: in the direction of growth.

loose-lying: not attached to but lying free, on or over the substratum.

lopadolith: in coccolithophorids, a barrel-shaped coccolith that opens distally.

lorica: a protective case containing a naked (non-walled) cell.

lubricous: smooth, slippery.

lumen: the cytoplasmic centres of a cell or filament; pl. lumina.

lumpy: a thallus with short, swollen protuberances that are usually unbranched and are often crowded or contiguous.

lunate: half-moon-shaped.

lysosome: a vesicle containing enzymes capable of decomposing various types of compound; sometimes also used to refer to vesicles containing the remains of organelles (often membrane profiles) that have been broken down.



macrandous: in Oedogoniales (Chlorophyta), without dwarf males (nannandria); the sexual zoids formed by the cells of the male filaments function directly as male gametes and do not first give rise to minute male plants (dwarf males).

macroalgae: algae visible to the naked eye.

macrococcolith: in coccolithophorids, a coccolith with an almost circular, proximal disc and a funnel-shaped, upper part.

macrogametangium: a gametangium with relatively large locules, producing macrogametes; pl. macrogametangia.

macrogamete: the larger (usually regarded as female) of anisogametes.

macroscopic: clearly visible with the naked eye.

macrothallus phase: the phase of a heteromorphic life history in which a relatively large, usually well-differentiated thallus is produced.

macrozoid: the larger of two differently-sized zoids.

macrozoosporangium: a sporangium with relatively large locules, producing the larger of two differently-sized spores; pl. macrozoosporangia.

maintenance culture: a natural collection of algae kept alive in the laboratory.

mamilliform: nipple-shaped; of a papillate protuberance.

mangroves: arborescent angiosperms characteristic of essentially marine, intertidal, usually mud-flat habitats in tropical to warm-temperate seas, usually with modifications of the roots (e.g. presence of pneumatophores).

mannan: a polysaccharide wall component that yields mannose on hydrolysis.

mannitol: a polyhydroxyalcohol derived from the hexose monosaccharide mannose.

manubrium cells: in Characeae (Chlorophyta), columnar or fist-shaped, radially oriented cells in the antheridium, lying on the inner side of the shield cells.

marginal ridge: in diatoms, a ridge between the valve face and the valve mantle which may be continuous or interrupted, perforated or solid.

marine: pertaining to seawater, from coastal or oceanic areas.

mastigonemes: in Heterokontophyta and Cryptophyta, stiff, lateral hairs borne by a flagellum, each one c. 15 nm thick and consisting of a base, a tubular shaft, and several terminal hairs; = flimmer.

mating structure: in flagellated gametes of the Chlorophyta, a special portion of the plasmalemma (overlying one of the two 2-membered microtubular flagellar roots and a single or double plate of dark-staining material) where fusion begins with gametes of the opposite sex.

maturing face (secretory face): of a Golgi body, the side on which Golgi vesicles are cut off from the cisternae.

maupas body: in Cryptophyta, a probable lysosome vesicle lying at the anterior of the cell and filled with the remnants of membranes.

mean sea level: the mean of all the hourly heights of the sea level over a month or year.

median cingulum: in dinoflagellates, a cingulum located approximately at the endpoint of a cell.

medulla: the central region of a thallus, internal to the cortex.

medullary: pertaining to a medulla.

megacytic zone: in armoured dinoflagellates, a region of growth or expansion between adjacent plates where new thecal material is added to allow enlargement of a cell or following cell division.

meiocyte: a cell that undergoes meiosis.

meiosis: the process of nuclear division which results in the halving of the chromosome count from the diploid number (2n) to the haploid number (n), so that each haploid nucleus receives a complete set of chromosomes homologous to the sets received by the others. Meiosis consists of two successive divisions, so that four haploid nuclei arise from each diploid nucleus.

meiosporangium: a cell, often with a characteristic shape and structure, the contents of which divide into meiospores.

meiospore: a spore formed directly as a result of meiosis and therefore haploid.

membranous: delicate and often transparent/translucent.

meriblastic: branching by outgrowth of small peripheral cells on the axis.

meristem: an apical, intercalary or diffusely positioned region of actively dividing cells and generally recognisable by the comparatively smaller size of the cells.

meristoderm: a tissue at the surface of a thallus (i.e. an epidermis) which behaves meristematically, i.e. in which the cells divide frequently.

meroplanktonic: of organisms that spend part of their life history as a planktonic stage and a part as a benthic, usually resting, stage.

mesochiton collar: in the Seirococcaceae (Phaeophyceae), the thickened, collar-like, inwardly projecting ring of central wall material near the apices of oogonia.

mesokaryotic: in dinoflagellates, a nucleus in which the chromosomes persist in a condensed, discrete state at all times.

mesoplankton: plankton organisms in the size range of 200–2000 µm.

mesospore: the central layer of a wall in thick–walled spores or zygotes.

mesotrophic: intermediate between eutrophic and oligotrophic; said of water quality or organisms in habitats somewhere between pristine and polluted.

metaphase plate: the plate-like arrangement of chromosomes at the equator of the spindle at metaphase.

metaphase: the stage in nuclear division when the chromosomes are maximally contracted and become arranged at the equator of the spindle, shortly before the chromatids move apart to the spindle poles.

microbody: = peroxisome.

micrococcolith: in coccolithophorids, a coccolith, not necessarily smaller than a macrococcolith, with an oval, proximal disc and a distal part drawn into a very short tube with an upper brim.

microfibril: a minute, submicroscopic fibrillar component of cell walls.

microfilament: a submicroscopic protein filament in eukaryote cells (visible with the electron microscope), including actin filaments.

microfossil: microscopic fossils.

microgametangium: a gametangium with relatively small locules, producing microgametes; pl. microgametangia.

microgamete: the smaller (usually regarded as male) of anisogametes.

micrometre: 10−6 m; = µm (1000 to a millimetre).

micropalaeontology: the study of microfossils; cf. fossil.

microplankton: plankton in the size category 20–200 µm; cf. nanoplankton (2–20 µm) and picoplankton (0.2–2 µm).

microscopic: small structures seen clearly only with a microscope.

microsporangium: a sporangium producing microspores.

microspore: in diatoms, the product of division prior to spermatogenesis (the spherical microspores undergo meiosis, each giving rise to four sperms).

microthallus: the phase of a heteromorphic life history in which a relatively small and undifferentiated thallus is produced.

microtubular root: a bundle of one to many parallel microtubules which extends down into the cell from a flagellar basal body; cf. flagellar roots.

microtubule organising centre (MTOC): an area within a cell from which microtubules arise and grow; cf. centriole.

microtubule: a very fine, tubular structure (diameter 25 nm) in the protoplasm which can be resolved with an electron microscope. It consists of 13 rows (proto-filaments) of globular protein (tubulin) molecules, closely associated laterally to form a cylinder. Microtubules are part of the cell skeleton (cytoskeleton) and also play a role in certain cellular movements such as flagellar bending (when microtubules of an axoneme slide along each other) and in the movement of chromosomes in a mitotic spindle, which also consists of microtubules.

microzoospore: an asexual, motile spore of small size relative to others produced by the organism.

midlittoral: applied to the middle portion of the intertidal zone.

midrib: a thickened line of cells or tissue running longitudinally through the middle or main axis of a leafy frond or compressed branch of a thallus.

mitosporangium: a sporangium producing mitospores; pl. mitosporangia.

mitospore: a spore formed as a direct result of mitosis, of the same ploidy level as the parent thallus.

Miocene: a geological epoch (5–24 Ma) within the Cenozoic Era (65 Ma to the present).

mitochondrion: an organelle of eukaryotic cells surrounded by a double membrane and responsible for respiration; the inner membrane projects into the lumen of the mitochondrion in a series of folds (cristae) or tubes; pl. mitochondria.

mitosis: the process of nuclear division which results in both daughter nuclei receiving identical sets of chromosomes following replication of the chromosomes during the preceding cell cycle; the sets inherited by the daughter cells are also identical (in the absence of mutation) to the set possessed by the parent cell.

mitospore: a spore formed as a direct result of mitosis (normal nuclear division).

mixotrophy: the taking up of organic substances by a phototrophic organism for supplementary nutrition (e.g. by phagotrophy).

MLS: see multilayered structure.

monad: a solitary, flagellate cell (unicellular flagellate).

moniliform: arranged like a string of rounded beads.

monoecious: producing male and female gametes on the same individual; cf. hermaphroditic.

monomerous: in non-geniculate Corallinales (Rhodophyta), having a type of thallus construction involving a single pseudoparenchymatous system of repeatedly branched filaments that form a core in which the filaments are oriented more-or-less parallel to the thallus surface, and a peripheral region in which portions of filaments become oriented more-or-less perpendicular to the thallus surface; cf. dimerous.

monomorphic: in coccolithophorids, having a coccolith case bearing one type of coccolith.

monophasic: having a single ploidy level (e.g. haploid or diploid) in the normal life history.

monophyletic: a circumscribed taxon descended from a single ancestor.

monopodial: growing by means of a continuous, apical growing point.

monosiphonous: having a single central siphon.

monospecific: belonging to a single species, e.g. a monospecific bloom consists of a single species; cf. monotypic.

monosporangium: a sporangium in which only one spore (a monospore) is produced.

monospore: the single, asexual spore produced by a monosporangium.

monostromatic: single-layered, only one cell thick.

monotypic: a taxon with only a single subordinate taxon, e.g. a genus containing only one species; cf. monospecific.

morphology: the form of a thallus or structure.

muciferous body: in unicellular, flagellate algae, a vesicle, containing mucilage, which lies beneath the plasmalemma and often discharges its contents upon stimulation.

mucilage-filled: of a thallus, having a partially hollow medulla that contains slimy, nonfibrillar polysaccharides.

mucilage: a jelly-like or slimy carbohydrate material.

mucilaginous: having a slimy or slippery texture.

mucocyst: in unicellular organisms, a vesicle secreting mucus-like substances.

mucopolysaccharide: glycosaminoglycan, a polysaccharide containing amino sugars and uronic acids; a mucopolysaccharide that attracts much water and binds it in a mucilaginous slime.

mucro: a short, sharp-pointed, terminal structure on the distal end of a cell.

mucronate: having a mucro.

multiaxial: a thallus resulting from the apical, meristematic activity of a number of consolidated filaments, each contributing equally; generally recognisable by the presence of a cluster of apical cells.

multicellular: consisting of many cells.

multifid: cleft into many branches or segments, and often said of spines.

multilayered structure (MLS): in some Chlorophyta, Glaucophyta and dinoflagellates, a flat, layered structure situated below the flagellar basal bodies and associated with a microtubular, flagellar root, the structure composed of two laminate layers containing differently orientated platelets and also incorporating the apical portion of a microtubular root; it contains many microtubules.

multinucleate: with few to many nuclei in the cell or coenocytic (acellular) thallus.

multiseriate: a filament with longitudinal divisions in its cells; = pluriseriate; cf. uniseriate.

muricate: rough-surfaced, with short, hard points.

mutic: without a terminal point.

murein: the peptidoglycan that forms the supportive, fibrillar layer of bacterial cell walls; a polymer composed of polysaccharide chains (in which there are alternating units of N-acetylglucosamine and N-acetylmuramic acid, linked by β-1,4-glucosidic linkages), linked by peptide bridges.

mycobiont: the fungal partner in a lichen.

myosin: a cytoskeletal protein composed of two globular heads and a 150 nm long double helix forming a rod-like tail. Myosin molecules associate to form thick filaments in animal muscles. Muscle contraction is caused by the sliding of actin filaments (the thin filaments of muscles) along the myosin heads. Interaction between actin and myosin is also involved in the generation of cytoplasmic streaming in the cells of certain algae (e.g. Bryopsidophyceae), but details of the mechanism are unknown.

myrionemoid: of a thallus, resembling Myrionema (Phaeophyceae) in being heterotrichous with a monostromatic basal layer.



naked: lacking a cell wall; cf. unarmoured.

nannandrium: see nannandrous.

nannandrous: in Oedogoniales (Chlorophyta), possessing dwarf males (nannandria). The sexual zoids produced by the male filaments function as spores (androspores), which grow into minute male filaments (nannandria). These then produce the male gametes (spermatozoids).

nanocyte: in Cyanophyta, a dwarf cell formed from a normal cell following a series of cell divisions in which the daughter cells do not significantly enlarge.

nanometre: 10−9 m; = nm (1 000 000 to a millimetre).

nanoplankton: plankton organisms in the size range 2–20 µm.

necridium: in filamentous Cyanophyta, dead cells that bracket hormogonia.

nemathecium: a raised, fertile patch; pl. nemathecia; cf. sorus.

nematocyst: a cell organelle that shoots out a harpoon-like spine when stimulated; = cnidocyst.

neotype: a specimen selected to serve in place of the holotype when no original type material is extant.

neritic zone: the area of continental shelf where the sea bottom is no deeper than 200 m; coastal waters; cf. pelagic, oceanic.

neuston: a community of organisms living at the water-atmosphere interface, often attached to the meniscus (as in choanoflagellates).

neutral sporangium: a sporangium producing mitospores that recycle the same phase of the life history.

nexin link: in the axoneme, a protein link between the nine peripheral doublets.

nitrogen fixation: an anaerobic chemical process, performed by some bacteria and cyanophytes, in which nitrogen gas (N2) is reduced to ammonium (NH4+) by the enzyme nitrogenase.

nm: see nanometre.

node: a site on a main axis where lateral branches or appendages arise.

nom. cons.: nomen conservandum, or a name conserved against a previously published legitimate name according to the rules of the International Code of Botanical Nomenclature.

nom. dub.: nomen dubium, a doubtful name, to be disregarded under older (pre-1975) versions of the International Code of Botanical Nomenclature, now usually dealt with by conservation or rejection.

nomenclatural type: the single specimen, or element of a collection, or effectively published illustration on which a taxon’s name is based.

non-articulated: not segmented into genicula and intergenicula.

non-geniculate: lacking genicula, or uncalcified joints.

non-striated connective: see transversely striated connective.

nori (Japanese): dried sheets of the edible red alga Porphyra.

nucleohistone: = histone.

nucleoid: in prokaryotes and in mitochrondria and chloroplasts of eukaryotes, an aggregation of DNA which somewhat resembles a nucleus but lacks a nuclear envelope and histones; cf. nucleoplasm.

nucleolus: a spherical body within the nucleus producing cytoplasmic ribosomes consisting of proteins and RNA.

nucleomorph: in Cryptophyta, Chlorarachniophyta and some dinoflagellates, an organelle closely associated with a chloroplast, containing DNA and enclosed by a double membrane envelope; purportedly the vestigial nucleus of a photosynthetic, eukaryotic endosymbiont.

nucleoplasm: in Cyanophyta, the part of the centroplasm containing the DNA; cf. nucleoid.

nullipore: obsolete term formerly used to describe the non-articulated coralline algae to contrast them with the true corals, in which the numerous pores each housed a feeding polyp.

nutritive auxilary cell: in Florideophyceae, a cell, usually in or near the carpogonial branch, providing nutrition to the connecting filament; the connecting filament fuses with this cell before extending to the generative auxiliary cell; cf. auxiliary cell.

nutritive cell (filament): in Florideophyceae, a cell or filament supplying nutrition to other cells (e.g. the developing carposporophyte), usually darkly staining and communicating by open (non-plugged) pit connections to contiguous distal and, usually, proximal cells.



obconical: conical in outline, but attached at the narrower end.

oblanceolate: lance-shaped, but attached at the narrower end.

obovate: ovate in two–dimensional profile, but attached at the narrower end.

obovoid: egg-shaped (three-dimensional), but attached at the narrower end.

obtuse: blunt or rounded at the apex.

oceanic: living at sea, away from and independent of coastal influences; cf. pelagic.

ocellus: in certain dinoflagellates, a light-;perceiving organelle consisting of a large refractive lens and a pigment-containing cup; in diatoms, a zone of less differentiated areolae surrounded by a discrete rim.

oligotrophic: nutrient-poor (can mean ‘poor in nutrient salts’ or, by extension, ‘with low primary production’); with fewer than 100 ppm of solutes; cf. eutrophic, mesotrophic.

ontogeny: the process by which an adult organism develops from the youngest stage.

ooblast: a connecting filament that transfers a zygote nucleus from a carpogonium to an auxiliary cell.

oogamete: a non-motile, female gamete (= egg).

oogamy: fusion of a relatively small male gamete (usually motile) with a relatively large non-motile female gamete (egg cell).

oogonium mother cell: a cell that cuts off an oogonium.

oogonium: a cell (often with a characteristic shape and structure) whose contents divide up into egg cells, which may remain within the oogonium or be released; pl. oogonia.

oospore: a zygote or fertilised egg that develops a separate wall and later germinates directly as a filament.

open mitosis: mitosis in which the nuclear membrane disperses or disappears.

orbicular: flat with a circular outline; cf. globose (three-dimensional).

order: a taxonomic group ranked between class and family, the name ending in -ales.

ordinary coccolith: in coccolithophorids, cf. stomatal coccolith.

organelle: a differentiated structure within a eukaryotic cell, often membrane-bound, such as a nucleus, chloroplast or pyrenoid.

osmoregulation: regulation of the water content of the cell. If the cell sap of a wall-less cell is hypertonic (more concentrated) with respect to the surrounding medium, water will tend to enter the cell and must be removed by osmoregulation, e.g. by contractile vacuoles.

osteolith: in coccolithophorids, a femur-shaped coccolith, built up of lamellae.

ostiole: an opening in a thallus surface, leading to a reproductive cavity. adj. ostiolate; cf. pore canal.

ovate: egg-shaped in two-dimensional outline, broadest near the base or point of attachment.

ovoid: egg-shaped in three-dimensions, broadest near the base or point of attachment.

oxygenic: producing oxygen. In oxygenic photosynthesis, water is used as a donor of highenergy electrons and hydrogen (protons), with the formation of oxygen as a by-product, summarised thus: CO2 + 2H2O → [CH2O] + H2O + O2. Oxygenic photosynthesis is undertaken by the prokaryotic blue-green algae (Cyanophyta) and by photosynthetic eukaryotes; cf. anoxygenic.



pachytene: the stage of meiotic prophase during which homologous chromosomes are linked together in pairs by ‘synaptonemal complexes’ and begin to shorten through supercoiling. The synaptonemal complex is a zip-like structure formed between the homologues which can be observed with an electron microscope.

palisade: a row of elongate structures at right angles to the surface.

palisade cells: elongate cells in rows or tiers, often forming the outer layer of the cortex; in non-geniculate Corallinales, elongate vegetative cells in which the end walls (those having primary pit connections) are much longer (usually 2–4 times) than the side walls, and cell length is substantially less than cell height or diameter.

palmelloid: consisting of cells that are coccoid and proliferate within a mucilaginous matrix.

panicle: a loose cluster of reproductive organs; more precisely, a branched raceme.

paniculate: in a loose, pyramidal form.

pantacronematic: of a flagellum having two rows of mastigonemes and a terminal fibril; cf. pantonematic.

pantonematic: of a flagellum having two rows of mastigonemes but with no terminal fibril; cf. pantacronematic.

papilla: a small, rounded protuberance borne by a cell wall or envelope; pl. papillae; adj. papillate.

pappolith: in coccolithophorids, a heterococcolith having upright, marginal elements on a basal disc and in which the central area is partially covered by a single layer of elements arranged in rows or bars (a spine-like process may emerge from the central area).

paracrystalline: in ultrastructure, having a strictly-organised pattern of electron-dense, organic material.

paraflagellar body: = flagellar swelling.

parallel evolution: a process whereby two or more distantly related groups or organisms develop similar looking organs or traits.

paramylon: a storage polysaccharide composed of β-1,3-linked glucose residues, typically found in euglenoids.

paraphyletic: a taxonomic group not containing all descendents of a particular ancestor or elements of a clade.

paraphysis: a usually uniseriate, sterile filament lying between reproductive structures on the thallus surface or within conceptacles; pl. paraphyses.

parasexual recombination: a process that brings about genetic recombination without involving karyogamy and meiosis.

parasite: an organism growing on and at least partially dependent on the host for its nutrition; see hemiparasite, adelphoparasite, alloparasite.

parasporangium: a non-meiotic sporangium with many spores, usually occurring in clusters; pl. parasporangia.

paraspore: a spore produced by a parasporangium. paraxial rod: a cross-striated structure running parallel with the axoneme in certain flagella (= paraxonemal).

parenchyma: tissue composed of relatively equidimensional cells derived from divisions in several planes; appears in section as closely abutting cells with few intercellular spaces; adj. parenchymatous; cf. filamentous, pseudoparenchyma.

parietal: internal and adjacent to the periphery of a cell or structure, e.g. a parietal chloroplast is a chloroplast that lies against the periphery of a cell.

parthenogenesis: development of a female gamete into an adult organism without fertilisation by a male gamete; also the development of male gametes or isogametes into adult organisms without the intervention of sexual fusion.

partition: a membrane-like structure traversing an otherwise hollow branch, usually a few cells thick.

patent: spreading.

pectinate: descriptive of a unilateral series of branches set close together like the teeth of a comb.

pedicel: a stalk.

pedicellate: having a cellular stalk, usually uniseriate; applied to reproductive structures.

peduncle: in dinoflagellates, an extensible pseudopod (cytoplasmic appendage) located near the flagellar pores in some photosynthetic as well as non-photosynthetic species; used to catch and either suck out or engulf a prey organism (another alga or a protozoan).

pelagic: living in the open ocean rather than in coastal or inland waters; cf. neritic, oceanic.

pellicle: in dinoflagellates, a thin, additional wall layer or envelope, made of cellulose and sporopollenin-like material, lying below the theca; sometimes a chemically resistant layer that can give rigidity to an ecdysial cell or other cells such as a developing hypnozygote; in Raphidophyceae and Cryptophyceae, a skin-like layer composed principally of protein, found around the cells of certain algae; a type of periplast; in Euglenophyta, a layer of interlocking, proteinaceous ribbons located next to the cell membrane.

peltate: shield- or umbrella-like, with a stalk from the centre of the lower surface.

penicillate: pencil-like; tufted as in an artist’s brush.

pentalith: in coccolithophorids, a coccolith of five calcite units arranged radially in a single plane.

peptidoglycan: a polymer consisting of cross-linked polysaccharide and polypeptide chains; the main constituents of the cell wall of Cyanophyta and some non-photosynthetic bacteria.

percurrent: extending in a more-or-less straight line from base to apex of a thallus as one or more well-developed axes.

perennating organ: a vegetative part that assists a plant to remain alive for more than a single year or growing season.

perennating: living for several years or growing seasons.

perennial: a thallus or part thereof that lasts for several years or growing seasons.

periaxial cell/filament: a cell or filament cut off from a parent axial cell but oriented obliquely or at right angles to it.

pericarp: in Rhodophyta, the envelope of haploid tissue surrounding the gonimoblast in a cystocarp.

pericentral cell: a periaxial cell of equal length and parallel orientation to the parent axial cell, generally from three to many per axial cell and closely jacketing it.

periclinal: having cell division by walls parallel to the surface of the tissue.

pericyst: in Sphacellariales (Phaeophyceae), a peripheral cell of the thallus differing in size, colour and contents from inner cells, and functioning as a dormant initial.

perinuclear: lying around the nucleus.

peripheral region: in non-geniculate Corallinales (Rhodophyta), the region of a monomerous thallus in which filaments or portions of filaments become oriented more-or-less perpendicular to the thallus surface.

peripheral: lying around the circumference of a cell or structure.

periphyton: a consortium of microbiota (algae, bacteria, protozoa, metazoa), extracellular mucilages, detritus and inorganic particles attached to solid surfaces in aquatic systems.

periplast: any membrane other than the cell membrane surrounding a cell body; cf. pellicle.

periplastidial compartment: in Heterokontophyta, Cryptophyta and Chlorarachniophyta, the narrow space between a chloroplast and the chloroplast endoplasmic reticulum.

periplastidial reticulum: in Heterokontophyta and Haptophyta, a network of interconnected tubules found in the periplastidial compartment which may serve to transport polypeptides from nucleus to chloroplast.

perithallus: see hypothallus.

perizonium: in pennate diatoms, part of the auxospore wall consisting of silicified bands in two series, one transverse to the auxospore axis and one longitudinal.

Permian: the last geological period (248–286 Ma) of the Palaeozoic Era (248–590 Ma).

peroxisome: an organelle bounded by a single membrane, and the site of oxidation of a variety of substances; = microbody. Molecular oxygen is used to oxidise material, with the production of hydrogen peroxide (H2O2), which is then used by the enzyme catalase or the oxidation of various other substrates, the formation of H2O being a by-product.

pervalvar axis: in diatoms, the axis through the centre point of the two valves.

petiolate: stalked.

petiole: the stalk of a leaf or leaf-like structure.

phaeophycean hair: a filament (without or with greatly reduced phaeoplasts) of uniseriate cells developing from a basal meristem of few to several dividing cells; cf. false hairs.

phaeoplast: the photosynthetic plastid of brown algae, distinguished by its brown colour, the presence of fucoxanthin and other pigments, and thylakoids in groups of three.

phagocytosis: uptake of a solid food particle or a prey organism by a cell through incorporation into vesicles pinched from the plasmalemma; cf. endocytosis, pinocytosis.

phagotrophic: of a unicellular organism, feeding on solid particles of food which are taken up into a food vacuole, often with the help of pseudopodia.

phenology: the study of periodic (seasonal) phenomena in an organism, or a community of organisms, in relation to environmental factors.

phenotype: the observable characteristics of an organism resulting from the interactions of the genotype and its environment.

pheromone: a substance produced by an organism which acts as a chemical signal to other individuals, e.g. a sexual attractant given off by a female to attract a male.

phialopore: in certain coenobic Volvocales, an intercellular space in an autocolony through which the colony everts by a process of the lips folding back. This turns the colony inside out and places the anterior ends of the constituent cells on the outside (as was the case with the parent colony).

phlorotannins: in Phaeophyceae, polymers of phloroglucinol (1,3,5-trihydroxybenzene) which exhibit the properties of tannins, precipitating proteins from solution and binding metal ions; they have an astringent taste.

photic zone: an illuminated zone of a waterbody within which plants and algae can sustain photosynthesis at rates greater than or equal to respiration.

photoassimilates: simple, low-molecular-mass sugars formed through photosynthesis; = photosynthates.

photoautotrophic: using light as a source of energy (capturing it with photosynthetic pigments) and using it to assimilate carbon from inorganic sources (principally carbon dioxide or bicarbonate), resulting in the formation of organic compounds; cf. photoheterotrophic, phototrophic.

photoauxotrophic: photosynthetic but requiring vitamins.

photobiont: the photosynthetic partner in a lichen.

photoheterotrophic: using light as a source of energy, but deriving carbon from organic compounds; cf. photoautotrophic, phototrophic.

photoinhibition: the inhibition of photosynthesis by high light irradiance.

photokinesis: movement stimulated by light, with speed correlated positively to light intensity.

photophobic response: a sudden reversal in movement in response to a sudden increase or decrease in light intensity.

photopigments: light-absorbing molecules located within the plastids of algal cells, or freefloating in cyanophyte cells, which are either directly involved in the light reactions of photosynthesis (i.e. chlorophyll), or which absorb light energy and transfer it to chlorophyll (i.e. accessory pigments such as carotenoids, fucoxanthin, phycocyanin, phycoerythrin).

photoreceptor apparatus: the whole complex of eyespot (stigma) and photoreceptor in flagellate algal cells. The photoreceptor contains a light-sensitive pigment and is situated either in a flagellar swelling (Heterokontophyta, Euglenophyta) or in a specialised area of the plasmalemma overlying the eyespot (Chlorophyta); cf. flagellar swelling.

photosynthates: = photoassimilates.

phototaxis: movement in response to light, towards (positive phototaxis) or away from it (negative phototaxis).

phototrophic: requiring light as a source of energy; cf. photoautotrophic, photoheterotrophic.

phragmoplast: a structure composed of the interzonal (continuous) spindle microtubules, together with various other microtubules around the periphery of the spindle (and lying parallel to it), involved in the assembly of a cell plate and hence also in the formation of a new cell wall, in the plane of the spindle equator; cf. phycoplast.

phycobilin: in Cyanophyta and Rhodophyta, water-soluble biliprotein pigments that absorb maximally in the shorter-wavelength end of the spectrum.

phycobilisome: in Cyanophyta and Rhodophyta, a minute, spherical or discoid body attached to the thylakoid, containing the accessory pigments phycoerythrin and phycocyanin.

phycocyanin: in Cyanophyta and Rhodophyta, blue biliprotein pigment.

phycoerythrin: in Cyanophyta and Rhodophyta, red biliprotein pigment.

phycology: the study of algae, equivalent to and generally replacing the older term algology.

phycoma: in certain Prasinophyceae, a cyst-like stage in the life history, with a wall resistant to bacterial degradation and probably containing sporopollenin-like material.

phycoplast: an assembly of microtubules at the equator of the spindle during telophase. The microtubules are oriented with their long axes approximately in the equatorial plane, at right angles to the spindle axis. Cell division takes place in the plane of the phycoplast; cf. phragmoplast.

phycovirus: a virus growing in algal cells.

phylloid: leaf-like.

phylogeny: the evolutionary origin and derivation of organisms.

phylum: a major group of organisms, ranked above Class; an alternative name for Division under the International Code of Botanical Nomenclature (e.g. Chlorophyta, Rhodophyta, Dinophyta).

physiological anisogamy: the fusion of two gametes that appear the same morphologically, but behave differently (the male gamete moves towards the female); cf. anisogamy, isogamy.

physodes: vesicle-like globules in cells of most brown algae which contain phenolic compounds; = fucosan vesicles.

phytochrome: a pigment that occurs in two forms, one sensitive to red light, the other to farred light; instrumental in the perception of day length and the control of various developmental processes.

phytopathogen: an organism causing a disease of plants.

phytoplankton: primarily microscopic, photosynthetic algae that live free, suspended (or swimming feebly) in water.

picoplankton: planktonic organisms in the size range 0.2–2 µm.

pigmented: coloured.

pilose: hairy, usually covered in soft hairs.

pinna: a lateral of a distichous, regularly branched frond; pl. pinnae.

pinnate: with laterals, ramuli or segments arranged along opposite sides of an axis or branch.

pinnule: a lateral of a pinna.

pinocytosis: uptake of fluid by a cell through incorporation into vesicles pinched in from the plasmalemma; cf. phagocytosis, endocytosis.

pit: a break in the cell wall through which strands of cytoplasm extend, connecting adjacent cells.

pit connection: in Rhodophyta, a narrow, central channel resulting from incomplete wall formation at cell division; can be primary (resulting from cell division in an apical cell) or secondary (resulting from the cutting off of small lateral cells that fuse with adjacent, primary pit-connected cells).

pit plug: in Rhodophyta, a lens-shaped plug of proteinaceous material deposited in the pit connection between adjacent cells.

placoderm desmid: a desmid in which the cell walls of the semicells are of different age.

placolith: in coccolithophorids, a heterococcolith composed of an upper and a lower shield of radial elements interconnected by a tube.

plankton: mostly microscopic organisms that, although they may have limited motility and/or buoyancy control, drift at the mercy of winds and currents; adj. planktonic.

plano-convex: flat on one side and convex on the other side.

planozygote: a zygote that swims using flagella derived from the gametes that fused to produce the zygote.

plasmalemma: a membrane bounding a cell; cf. cell membrane.

plasmid: a small circular molecule of DNA capable of independent replication. Plasmids are of general occurrence in prokaryotes but also occur in eukaryotic cells.

plasmodesmata: in some Phaeophyceae and Chlorophyta, thin, protoplasmic connections through microscopic perforations between two cells.

plasmodium: a multinucleate protoplast without a cell wall which exhibits amoeboid movement.

plasmogamy: the fusion of the protoplasts of two gametes; cf. karyogamy.

plasticity: the capacity of an organism to change its form in response to varying environmental conditions.

plastid: an organelle enclosed by a double membrane which either contains thylakoids and photosynthetic pigments (chloroplasts) or stores carbohydrate (amyloplasts); plastids are often discoid or band-shaped.

plastidome: the complement of plastids in a cell.

pleiomorphy: the ability of organisms to exhibit two or more different forms in their life history.

plesiomorphic: of a character, shared more widely than the group under discussion, often described as ancestral or primitive; cf. autapomorphic, apomorphic, synapomorphic.

plethysmothallus: in certain Phaeophyceae, a haploid or diploid, microthallic phase capable of asexual multiplication by zoospores and of direct development into a macrothallus.

pleuronematic flagellum: in Cryptophyta and Heterokontophyta, a flagellum bearing hairs, especially stiff hairs (mastigonemes).

ploidy: the number of complete sets of chromosomes in a cell (e.g. haploid, diploid).

plumose: feathery.

plurilocular: a sporangium or gametangium having many chambers, each locule producing a mitospore or gamete.

plurilocular zoidangium: in Phaeophyceae, an organ containing many chambers (loculi), each one of which produces a single zoid.

pluriseriate: = multiseriate.

plurispore: a spore produced from a plurilocular sporangium.

pluristromatic: formed of several to many layers of cells or stroma.

plurizoid: in Phaeophyceae, a zoid produced by a plurilocular zoidangium.

pneumatocyst: a vesicle; a gas-containing, subspherical to ovoid flotation structure.

pneumatophore: a vertical, aerial (at low tide) appendage to the roots of mangroves through which gaseous exchange occurs.

polar coccolith: in coccolithophorids, a coccolith type occurring only in the polar regions.

polar fenestrae: openings in the nuclear envelope at the poles of the spindle during closed mitosis.

polar nodule: in Cyanophyta, a rounded thickening of the cell wall between a heterocyst and the one or two immediately adjacent cells, through which reductants pass to the site of the nitrogenase enzymes; in raphid pennate diatoms, a thickening near the end of the valve.

polar plates: in diatoms, a dark-staining, plate-like structure at the poles of the mitotic spindle.

polar rings: in Rhodophyta, dark-staining, ring-like bodies at the poles of the mitotic spindle; probably part of the microtubule organising centres (MTOCs).

polychotomous: of branching, with numerous, equal or subequal branches arising from a node.

polyeder: in some Chlorococcales (Chlorophyceae), an irregularly shaped, polyhedral cell developing from a meiospore and giving rise to young colonies.

polyhedral body: = carboxysome.

polymorphic: occurring in many morphological forms.

polymorphism: in coccolithophorids, a coccolith case bearing more than two types of coccoliths.

polyphosphate granule: a microscopic granule of highly polymeric phosphate.

polyphyletic: pertaining to a non-natural group composed of descendants from several or many different ancestors.

polypyramidal pyrenoid: a radially subdivided pyrenoid covered by a number of radially arranged starch grains.

polysaccharide: a macromolecule composed of sugar monomers.

polysiphonous: having many siphons, i.e. consisting of parallel rows of elongate cells, packed close together; specifically, of many Ceramiales (Rhodophyta) in which the axis is ringed by pericentral cells.

polysporangium: a sporangium producing many meiotic spores, homologous to a tetrasporangium; pl. polysporangia.

polyspore: one of many haploid spores in a polysporangium.

polystichous: in certain Phaeophyceae, having the thallus truly parenchymatous.

polystromatic: with several layers or stroma.

pore: in Corallinales (Rhodophyta), the opening above a reproductive structure.

pore canal: a canal in a conceptacle roof through which spores or gametes pass; cf. ostiole.

pore plate: in Corallinales (Rhodophyta), the roof of a multiporate conceptacle containing the pores and pore canals.

poroid areola, poroid: in diatoms, an areola not markedly constricted at one surface of the valve; cf. loculate areola.

porphyran: a sulfated polysaccharide of Porphyra (Rhodophyta) composed of galactose units.

postigenous filament: any of the filaments in a dimerous thallus which arise at right angles from cells of primigenous filaments.

postmedian cingulum: in dinoflagellates, in dinokont-type cells when the cingulum is below the midpoint of the cell; cf. premedian cingulum.

ppm: parts per million.

Precambrian: the long period of time (590–4500 Ma) before the appearance en masse of invertebrate fossils; comprising the Priscoan (4000–4500 Ma), Archaean (2500–4000 Ma) and Proterozoic Eras (590–2500 Ma). Some Precambrian limestone rocks in Australia contain stromatolites, believed to be formed by Cyanophyta.

precursor: a compound or structure that precedes another in a chemical or developmental pathway and is transformed or incorporated into it.

premedian cingulum: in dinoflagellates, in dinokont-type cells, a cingulum above the midpoint of the cell; cf. postmedian cingulum.

primary consumer: a consumer of primary producers (in most cases, therefore, of plants or algae); = herbivore.

primary fascicle: in Batrachospermales (Rhodophyta), a determinate lateral arising from a pericentral cell.

primary filament: in Fucales (Phaeophyceae), a type of filament comprising (along with secondarily formed fibres) the medulla.

primary nucleus: in some siphonous Chlorophyta, the first nucleus that becomes relatively enlarged .

primary ooblast: in some Rhodophyta, a portion of a connecting filament linking a fertilised carpogonium to a cell in the carpogonial branch or to a nutritive auxiliary cell situated elsewhere.

primary pit connection: in Rhodophyta, a pit connection between adjacent cells of the same filament.

primigenous filament: in Corallinales (Rhodophyta), any filament that is directly traceable to a germinating spore and collectively forms the unistratose layer in a dimerous thallus; see also hypothallus.

primordium: a primary cell or immature state of a branch or structure; pl. primordia.

proboscis: a snout-like projection at the anterior end of the spermatozoid of Fucus (Phaeophyceae) and Vaucheria (Xanthophyceae), the shape being maintained by microtubules.

procarp: in certain Rhodophyta, a compact, female reproductive structure wherein the carpogonial branch is spatially related in a consistent way to the generative auxiliary cell that it diploidises following fertilisation.

procarpic: a close association of a supporting cell, carpogonial branch and auxiliary cell in the one branch system.

process: in diatoms, a projection with homogeneously silicified walls.

procumbent: lying along the substratum.

progressive cleavage: a form of cell division where several rounds of nuclear division occur first, producing a multinucleate cell which then divides into uninucleate daughter cells by branching invaginations of the plasmalemma.

prokaryotic: of an organism, lacking membrane-bound organelles (e.g. chloroplasts, mitochondria, nuclei) in the cell (bacteria and blue-green algae).

proliferous: bearing branchlets as irregularly placed offshoots.

propagule: asexual reproductive organ that is shed as a unit, including the outer cell walls (in contrast to being released from a sporangium); sometimes used loosely to refer to any reproductive unit.

prosthetic group: a non-protein group attached to a protein.

prostrate: lying flat on the substratum.

protandry: the maturation of male organs before female organs; adj. protandrous.

proteobacteria: gram-negative bacteria with no organelles, including a diverse range of organisms such as the purple, phototrophic, nitrifying bacteria and enteric bacteria as well as the bacteria responsible for animal bioluminescence.

Proterozoic Era: an early geological era (590–2500 Ma) with rocks containing microfossils of Cyanophyta and bacteria but few other fossils, except towards the end, when invertebrates appear.

protists: the collective name for the large, heterogeneous group of (mainly) unicellular organisms — some plant-like, some animal-like, some with features of both kingdoms — which comprise the ‘lower’ eukaryotes.

protofilament: = microtubule.

protologue: in nomenclature, everything written about an organism when its scientific name is first published.

protonema: in Characeae (Chlorophyta), the product of germination of a zygote from which the erect plant directly arises.

protosphere: in Bryopsidophyceae (Chlorophyta), in the life histories of some siphonous green algae, a spherical stage that develops from a germinating zygote and contains a giant nucleus.

prototrichogyne: in Bangiophyceae, the small, emergent portion of a female gamete cell that is receptive to spermatia.

protozoa, protozoan: informal names for heterotrophic, unicellular eukaryotes, a phylogenetically heterogeneous group.

protuberant: projecting, prominently raised from the surface of the thallus.

proximal: nearest to the point of attachment.

proximal sheath: in flagellate cells of some Chlorophyta, a sheath of amorphous, darkstaining material which lies appressed to the proximal side of each basal body. psammobious, psammophilic: pertaining to a preference for sand habitats (e.g. species living in the interstitial water of sandy beaches).

pseudodichotomous: dichotomous branching resulting from the equal growth of derivatives of the apical cell and subapical cell, not (as in true dichotomous branching) from the equal division of an apical cell.

pseudodisc: a structure having the appearance of a disc but comprising irregularly adjoining and associated filaments.

pseudofilament: a uniseriate row of cells spaced relatively distantly within a gelatinous sheath.

pseudoflagellum: an immobile, non-functional flagellum.

pseudogranum: a granum-like stack, formed by the partial overlap of a number of thylakoids.

pseudolateral: a hair or branch system displaced to a lateral position as a result of sympodial growth.

pseudoparenchyma: tissue with the appearance of parenchyma but derived from the close aggregation of uniseriate filaments, usually into a medulla of inflated or subspherical cells; adj. pseudoparenchymatous; cf. parenchyma, filamentous.

pseudopodial collar: in choanoflagellates, a ring of thin pseudopodia making a wide funnel around the flagellum.

pseudopodium: a plastically deformable protrusion of a naked cell, functioning in cell motility or the uptake of solid particles of food; pl. pseudopodia; cf. rhizopodium.

pulvinate: hemispherical or cushion-shaped, with a broad base.

punctate: with a dot-like appearance.

punctum: a small dot; in diatoms, a pore or other structure in a wall barely visible with a light microscope and only shown in detail by an electron microscope; pl. puncta.

pustule: a blister- or pimple-like structure.

pusule: in dinoflagellates, a more-or-less branched system of tubes lined by the plasmalemma and opening to the exterior of the cell.

pycnocline: a boundary between two layers of water marked by a sudden and dramatic increase in density over a small increase in depth.

pyknotic nucleus: a nucleus whose contents are degenerating and have become condensed.

pyrenoid: a usually spherical or ellipsoidal structure within the chloroplast visible under the light microscope. Embedded in the chloroplast, or lying beneath its surface and containing few or no thylakoids, a pyrenoid contains the enzyme RuBisCO and acts as a centre for carbohydrate (e.g. starch) synthesis. Reserve polysaccharides are formed near them (within the chloroplast in the Chlorophyta but outside in other groups).

pyriform: pear-shaped (three-dimensional) and attached at the narrow end.



quadriflagellate: having four flagella.



raceme: a cluster of reproductive organs where the main axis continues to grow, producing reproductive organs laterally; the youngest organ is therefore at the apex.

radial spokes: in an axoneme, radial links, consisting of protein, between the nine peripheral doublets and the central pair of microtubules.

radial: organised around a central point or axis.

radiolarians: in Polycystinea (Actinopoda), marine planktonic protozoans with stiff, radiating rhizopods and elegant, siliceous skeletons that are radially symmetrical.

ralfsioid: of a thallus, resembling Ralfsia (Phaeophyceae) in being pseudoparenchymatous and crustose.

ramification: the pattern of branching of an organism, or the process of branching or separating into branches.

ramulus: a smaller branch; pl. ramuli.

raphe: in some pennate diatoms, a longitudinal fissure through a valve associated with and involved in gliding locomotion and with cementing frustules to the substratum (adhesion).

receptacle: a specialised structure in which reproductive organs are aggregated; in Fucales (Phaeophyceae), swollen regions in which the conceptacles are embedded.

red alga: a member of the Rhodophyta.

red tide: see water bloom.

reduction division: = meiosis.

reflexed: bent backwards or downwards.

refract: bent from the base backward.

refractive: of the contents of a cell, appearing dense and uniform in transmitted light, usually darkly staining.

reniform: kidney-shaped.

reproduction, asexual: an increase in number of individuals but not involving gametic union.

reproduction, sexual: an increase in number of individuals involving usually union of gametes (plasmogamy), of their nuclei (karyogamy), association of their chromosomes and meiosis.

reservoir: in Euglenophyta, the sack-like dilatation beyond the canal.

resting spore: = hypnospore.

reticulae: in dinoflagellates, surface ornamentation on thecal plates where raised, straight or irregular lines cross one another forming a network or mesh of varying shape and size.

reticulate: net-like.

retrorse: turned or projecting backwards.

rhabdolith: in coccolithophorids, a heterococcolith having a basal circular to ellipsoidal disc and an elevated central region extending distally from the coccosphere.

rhinote: nose-shaped.

rhizine: in Gelidiales (Rhodophyta), a narrow, thick-walled filament with a minute lumen and walls that strongly refract in transverse section.

rhizoid: an accessory, attaching or absorptive structure, single- or few-celled; narrow medullary filaments produced from cells of component axes.

rhizoidal filament: a filament arising adventitiously from periaxial cells and extending along a central axis.

rhizoplast: a root-like, often transversely striated, contractile organelle composed of the contractile protein centrin and connecting the flagellar basal bodies to the nucleus.

rhizopodium: a thin, thread-like pseudopodium.

rhizostyle: in Cryptophyta, a straight, longitudinal microtubular root (composed of 6–10 microtubules) that descends from the basal body of the longer flagellum towards the posterior end of the cell.

rhodolith: in Corallinales (Rhodophyta), an unattached, commonly nodular thallus that develops as a result of fragmentation or envelopment of a stone or other object.

rhodoplast: the photosynthetic plastid of the Rhodophyta containing single thylakoids bearing the phycobilin pigments. rhombic scale: a scale that takes the form of a parallelogram.

ribes: in dinoflagellates, supports for sulcal lists.

ribosome: a minute, granular structure (c. 20–30 nm diam.), composed of RNA (ribonucleic acid) and proteins, and involved in the synthesis of proteins. The membranes of the endoplasmic reticulum are often studded with ribosomes (termed rough endoplasmic reticulum).

riffle: a shallow, fast-flowing section of a stream channel.

rootlet: sometimes used to refer to root-like components of the flagellar apparatus.

rosette: the pattern formed by a ring of small cells around the margin of a larger inner cell.

rough endoplasmic reticulum: endoplasmic reticulum (ER) studded with ribosomes.

RuBisCO: ribulose 1,5-biphosphate carboxylase-oxygenase, the enzyme catalysing the primary dark reaction of photosynthesis that involves the fixation of CO2 into carbohydrate.

ruffled: with a strongly waved or undulate margin.

rugulose: somewhat wrinkled.



saccate: hollow, in the form of a sac.

sagittate: shaped like an arrowhead.

salina: a hypersaline area.

saprotrophic: obtaining nutrition by taking up (through the plasmalemma) organic substances that have already been partly broken down outside the cell; living on decaying organic matter.

sarcinoid: composed of three-dimensional packets of cells.

saxicolous: growing on rock.

saxitoxin: neurotoxin produced by some dinoflagellates.

scalariform conjugation: in Zygnemaceae (Chlorophyta), reproduction in which the connected filaments and their conjugation canals appear like the rungs of a ladder.

scale: an organic or mineralised structure of specific architecture deposited on the cell surface.

scale reservoir: in unicellular or colonial algae where the cells are covered by scales, an invagination of the plasmalemma into which scales are secreted after being manufactured in Golgi cisternae. From the reservoir the scales are distributed over the cell surface.

scale theca: a close-fitting cell investment composed of minute, organic scales merged to form a wall-like structure.

scapholith: in coccolithophorids, a diamond-shaped heterococcolith with a central area of transverse lamellae intermeshed in the middle.

scarious: thin, dry and membranous.

schizogenous: developed by splitting of the tissue.

sclerenchymatous: having secondarily much-thickened cells or cell walls.

scytonemin: a pigment, produced in the mucilaginous sheaths of some cyanophytes, which absorbs ultraviolet radiation and probably has a protective function.

SDV: see silica deposition vesicle.

seagrass: a marine, monocotyledonous, flowering plant growing submerged at least at high tide, and undergoing underwater pollination.

secondary consumer: a carnivore that eats primary consumers.

secondary fibre: in Fucales (Phaeophyceae), a filament produced secondarily which contributes to the formation of the medulla.

secondary ooblast: in Rhodophyta, a connecting filament linking an auxiliary cell with a cell in a carpogonial branch other than the carpogonium (i.e. with a nutritive auxiliary cell).

secondary pit connection: in Rhodophyta, a pit connection formed between cells of two adjacent filaments.

secretory cell: a specialised cell that secretes mucilage; see gland cell, vesicular cell.

secund: bearing laterals more-or-less in a row on one side of a branch.

sediment: material (sand, salt, gravel etc.) deposited by water, ice or air.

sedimentary rock: rock formed through consolidation of sedimented (settled) sand, silt, gravel etc.

segment: a unit of a constricted branch.

segregative cell division: in Chlorophyta, a form of cell division in which a multinucleate protoplast divides into several often rounded daughter protoplasts that subsequently become surrounded by a wall. Each daughter cell then enlarges into an adult cell; cf. successive bipartition, eleutheroschisis.

seirosporangium: a sporangium formed in a simple or branched chain of sporangia; pl. seirosporangia.

seirospore: a spore produced by a seirosporangium. self-compatible: see heterothallic.

semicell: one of the two (usually identical) halves of a desmid cell.

semiconservative replication: of DNA, unwinding of the double helix so that each half acts as a template for a new half-helix; of a basal body, formation of a new basal body close to an existing one, which seems to act as a template for the new one.

septate: having cross-walls in cells or filaments which are shared by the sibling cells.

septum: in diatoms, a sheet or ridge in the valvar plane projecting from a girdle band into the interior of a frustule, often with several openings; more generally, a cross-wall; pl. septa.

serially arranged: disposed in a row, one behind the other.

seriate: arranged in a series on an axis.

serrate: marginally toothed, with the teeth pointing forwards.

serrulate: serrate with very small teeth.

sessile: attached directly, without a stalk.

seta: a stiff hair or bristle; in diatoms, a hollow projection of the frustule extending beyond the valve margin; pl. setae.

sheath: the surrounding fibrillar or amorphous substance or tissue of an organ.

shield cell: in Characeae (Chlorophyta), a shield-shaped cell forming the outer wall of an antheridium.

short shoot: = determinate lateral.

short-day response: a response to the perception of relatively short periods of light, or to light of a shorter duration than a critical daylength (for instance, of 14 hours light per day).

sieve area/plate: in some Laminariales (Phaeophyceae), a field of pores lined by plasmalemma and through which photoassimilates are translocated.

sieve element: a cell with a sieve area.

sieve tube: a longitudinal series or file of sieve elements.

silica deposition vesicle: in diatoms, a membrane-bound vesicle within a cell in which silica is deposited (e.g. individual elements of diatom frustules).

silicalemma: in diatoms, a membrane of a vesicle in which silica deposition occurs.

silicoflagellate: a member of the order Dictyochales (Chrysophyceae) characterised by an internal, siliceous skeleton.

siliquose: resembling a siliqua, an angiosperm fruit more than twice as long as wide and divided longitudinally into two.

Silurian: a geological period (408–438 Ma) in the Palaeozoic Era (248–590 Ma).

simple: unbranched or undivided.

sinistral: see imbrication, sinistral.

sinuous: with a wavy margin.

sinus: a recess between two structures.

siphon: an elongate or tubular cell without cross-walls; cf. filament.

siphonein: a carotenoid pigment in chloroplasts of certain coenocytic green algae, e.g. Caulerpales (Chlorophyta), which harvests light energy more effectively in deep water than chlorophyll.

siphonocladous: composed of multinucleate compartments (cells).

siphonous: with a thallus formed of multinucleate, tubular units cells (siphons).

siphonoxanthin: a carotenoid pigment (related to siphonein) in chloroplasts of certain coenocytic green algae, e.g. in Caulerpales (Chlorophyta), which harvests light energy more effectively in deep water than chlorophyll.

smooth endoplasmic reticulum (ER): an endoplasmic reticulum without ribosomes.

solitary: borne or growing singly.

sorus: a cluster of reproductive organs, often occurring as a surface patch or slightly raised group; pl. sori; cf. nemathecium.

spadix: a spike-like structure with a modified axis, usually enclosed in a spathe.

spathulate: elongate with the basal end narrower, as in a spatula or spoon.

spermatangiophore: in Rhodophyta, a structure that bears spermatangia.

spermatangium: in Rhodophyta, a cell whose contents differentiate into a spermatium; pl. spermatangia.

spermatangium mother/parent cell: in Rhodophyta, a cell that cuts off a spermatangium.

spermatium: in Rhodophyta, a non-motile or slightly amoeboid, non-flagellate male gamete; pl. spermatia.

spermatogenous thread: in Characeae (Chlorophyta), a filament enclosed in an antheridium the cells of which each gives rise to a single spermatozoid.

spermatozoid: a flagellate, male gamete produced in an antheridium; = antherozoid.

sphaeroid: = subspherical.

spike: in Characeae (Chlorophyta), a condensed branch system with lateral branches and gametangia.

spindle: an ellipsoidal or cylindrical bundle of spindle microtubules (seen in a light microscope as the spindle fibres) that converge towards each of the two spindle poles and are present at mitosis and meiosis. The spindle consists of interzonal (continous) microtubules that run from pole to pole, and chromosome microtubules that run from pole to chromosome.

spindle equator: the plane equidistant from the two spindle poles and lying between the daughter sets of chromosomes during anaphase and telophase.

spindle fibres, spindle microtubules: see spindle.

spine: a stiff, sharp-pointed projection on a cell or tissue.

splaying: spreading laterally or outwards.

spongiose: with the texture of a sponge.

sporangial complex: in the Sporolithaceae (Rhodophyta), a reproductive structure consisting of a sporangium within a calcified compartment that in turn is enveloped by a group of filaments that differ in appearance from ordinary vegetative filaments.

sporangium: a cell (often with a characteristic shape) in which spores are produced; pl. sporangia; cf. mitosporangium, meiosporangium.

spore: a one-celled reproductive structure derived by mitosis (mitospore) or meiosis (meiospore) and capable of growth directly; a cell released from a sporangium.

sporic meiosis: meiosis that occurs during the differentiation of spores.

sporocyte: a diploid cell that undergoes meiosis to form spores.

sporogenesis: development of spores.

sporogenous: giving rise to spores.

sporophyte: the diploid phase of the life history in which meiospores (by meiosis) or mitospores (by mitosis) are produced.

sporopollenin: a complex polymer derived from carotenoids which protects cells from drought. Some unicellular (e.g. Chlorella) and colonial (e.g. Scenedesmus) Chlorophyta contain sporopollenin-like material.

sporulation: the process of spore-formation.

spur: a horn-like extension to an organ.

starch: a storage polysaccharide composed of α-1,4- and α-1,6-linked glucose residues.

statospore: see endogenous cyst.

stellate pattern: in Chlorophyta, a nine-pointed star visible (in an electron microscope) in transverse sections of the flagellar transition zone. Centripetal contraction of the stellate structure (which contains the contractile protein centrin) may bring about abscission of the flagellum.

stellate: star-shaped, with numerous projections from a central region.

stenothermic: living within a narrow range of temperature and having a steep, optimum temperature curve.

stephanokont: with a ring or crown of flagella on the zoospore.

sterile: lacking reproductive organs of any type.

stichidium: in Rhodophyta, a specialised branch bearing meiotic, reproductive structures; pl. stichidia.

stichonematic: a flagellum with a single row of mastigonemes or hairs.

stigma: a red or orange-red spot (microgranule or oil droplet) usually confined to the chloroplast, often identical to an eyespot.

stipe: a stalk between the holdfast and the blade or frond of a thallus.

stipitate: having a lower, stipe-like region to the thallus; stalked.

stipulode: in Characeae (Chlorophyta), one-celled appendages in whorls occurring above and below a branchlet whorl.

stolon: a prostrate or creeping stem.

stoloniferous: stolon-like or stolon-bearing.

stomatal coccolith: in coccolithophorids, a coccolith associated with the stomatal (flagellar) area; cf. ordinary coccolith.

stomatocyst: a cyst, often silicified, with a narrow opening closed by a pectic plug.

stonewort: in Characeae (Chlorophyta), an informal name for a calcified species.

streblonematoid: with the form of Streblonema (Phaeophyceae), i.e. with prostrate, endophytic filaments bearing erect filaments that emerge from the host.

stria: stripe; in diatoms, one or more rows of areolae or pores in an alveolus; in dinoflagellates, surface ornamentation, on an unarmoured or armoured dinoflagellate, which appears as longitudinal lines or ridges; pl. striae.

striated strand: in dinoflagellates, a taut band of transversely striated material which keeps the transverse flagellum in place within the transverse groove. It contains the contractile protein centrin.

striations: more-or-less parallel markings.

stroma starch: starch grains lying in the stroma of a chloroplast, not in close association with the pyrenoid.

stromatolite: a concentrically layered, irregularly columnar, calcareous structure, formed usually by surface mats of Cyanophyta.

strut: in non-geniculate Corallinales (Rhodophyta), a branch that grows downward from the ventral surface of a thallus and aids in support.

stubby: short, thick and usually rounded.

stupose: covered with a felt of hairs.

styliform: having the shape of a style; generally slender and pointed.

sub- (as a prefix): nearly or almost, as in subspherical; a category below, as in subclass (below a class but above an order).

subaerial: = aerophytic.

subapical: shortly below the apex; commonly one cell (or more) below the apex.

subapical cell: the cell immediately proximal to an apical cell.

subcortex: the inner part of the cortex, often differentiated from the outer cortex, as, for example, in Chordariaceae (Phaeophyceae).

subdichotomous: nearly but not strictly evenly dichotomous.

subepithallial initial: in the Corallinales (Rhodophyta), a meristematic cell situated immediately beneath an epithallial cell.

subfasciculate: almost fasciculate; somewhat clustered.

sublittoral: the photic zone below the eulittoral region, from about mean low tide level to the lower limit of algal growth.

sublittoral fringe: a distinctive, fringing zone, sometimes characteristic of the region just below the eulittoral, e.g. in the suck-back of waves at low tide.

subsessile: almost sessile, with only a slight stipe or stalk present.

subspherical: almost spherical; = sphaeroid.

substratum: the underlying object(s) (e.g. rock, sand, mud or a host) to which an organism is attached; sometimes incorrectly called ‘substrate’; pl. substrata.

subtend: to be positioned at or just below the base of another organ.

subterete: almost terete.

subterminal: occurring or attached just below the terminal part of an organ, filament or cell.

subtidal: below the low tide mark, never exposed.

subtruncate: almost or only partially truncate.

subulate: long and more-or-less terete but tapering to a point.

successive bipartition: successive divisions of a uninucleate cell in which each division of the nucleus is followed by division of the cytoplasm, the daughter cells only later becoming surrounded by their own cell walls; cf. segregative cell division.

sulcus: in dinoflagellates, the longitudinal area on the ventral surface of a cell that forms a more-or-less pronounced furrow or depression housing the longitudinal flagellum. summer annual: an organism whose development, from spore to zygote to death, takes place in a single summer.

superior: in a position above a particular feature or structure.

supernumerary nuclei: the nuclei (commonly seven) that are rejected from inclusion in the egg cell following meiosis in the oogonium, e.g. in Cystoseiraceae (Phaeophyceae).

supporting cell: in Rhodophyta, a cell that bears a carpogonial branch; in Oedogoniales (Chlorophyta), a cell below the oogonium, both arising by division of an oogonial mother cell.

supralittoral: the region above the eulittoral (or about high tide level) occupied by organisms with marine affinities; the spray zone.

suture: in coccolithophorids and dinoflagellates, a seam or a furrow between adjacent parts; cf. inclination, clockwise, inclination, counterclockwise.

swarmer: = zoospore.

symbiont: an organism that lives symbiotically with another organism.

symbiosis: a very close association between two organisms (as between a fungus and an alga in a lichen); often used in the narrower sense of an association in which both partners derive some benefit (a mutualistic symbiosis).

symmetrical: in morphology, similar on both sides of a plane (bilateral symmetry) or around an axis (radial symmetry).

sympodial growth: a process in which an apical cell regularly loses its dominance and position to a lateral initial on the subapical cell; the lateral initial then becoming the new apical cell (cellulisympodial), or a similar process occurring at the branch level (ramisympodial).

synaptonemal complex: see pachytene.

synapomorphic: of a character, when apomorphic (derived) and shared by two or more taxa; cf. autoapomorphic, plesiomorphic, apomorphic.

synchronous: developing simultaneously, e.g. growth of branches.

synistosome: in Prasinophyceae, a fibrous, rectangular bar, striated longitudinally, which lies between the basal bodies.

synonym: in nomenclature, an alternative but incorrect scientific name for a taxon, either a nomenclatural synonym (a new combination or one that was coined later than a validly published name that has priority) or a taxonomic synonym (one that, in the opinion of a taxonomist, represents a taxon identical to the one in question, and again postdates the accepted name); cf. heterotypic synonym, homotypic synonym.

syntype: one of the specimens mentioned in the original description (protologue) of a taxon when no holotype was designated and more than one collection locality is given.

synzoospore: in Vaucheria (Xanthophyceae), a large, multinucleate zoospore bearing many pairs of flagella.



tabulation: in armoured dinoflagellates, the plate pattern as described by a standard numbering system.

tannin cell: a cell with dark polyphenolic inclusions.

tannins: see phlorotannins.

taxon: a group, at any level, in the classification of organisms; the general term for any systematic category (species, families, divisions are all taxa); pl. taxa.

telophase: the last stage of nuclear division during which the new daughter nuclei are formed at the poles of the spindle.

telophase spindle, non-persistent (collapsing): a mitotic spindle that collapses (disintegrates) in early telophase, long before cytokinesis; cf. telophase spindle, persistent.

telophase spindle, persistent: a mitotic spindle that persists through telophase to cytokinesis; cf. telophase spindle, non-persistent (collapsing).

temperate: a region with water temperatures ranging between 10° and 25°C.

template: a mould, complementary in shape or structure to the organelle or macromolecule formed in or against it.

tenacula: minute, lobed, hapteroid cells.

tenacular cells: cells with claw-like processes that form attachments to adjacent cells.

tendril: a slender climbing organ formed by modification of part of a plant.

terete: circular in cross-section, tubular in three dimensions.

terminal cap: in flagellate cells of certain Chlorophyta, a cap of dark-staining material which partly covers and occludes the lower (proximal) end of the flagellar basal body.

terminal cell: ultimate cell.

terrestrial: living on land.

Tertiary: the first and by far the longest geological period (1.8–65 Ma) of the Cenozoic Era (65 Ma to the present).

Tethys Sea: from the early Palaeozoic Era to the Miocene epoch, an elongate, largely tropical seaway, oriented east-west, which separated the northern and southern continents and connected the Indo-Pacific and Atlantic Oceans.

tetrahedrally divided/tetrahedral: of tetrasporangia, the arrangement of spores following a simultaneous division at slightly oblique angles (generally only three spores are visible in surface view and appear to occupy equal thirds of the sporangium).

tetrasporangium: the cell on the diploid, free-living sporophyte which undergoes meiosis to produce four haploid spores within the parent cell wall; pl. tetrasporangia.

tetraspore: one of the four meiospores produced by a tetrasporangium; germinating to produce a gametophyte.

tetrasporine: resembling Tetraspora (Chlorophyta), i.e. with cells that are separate but remain enclosed within a common mucilage envelope; similar to palmelloid.

tetrasporocyte: the precursor of a developing tetrasporangium before cleavage takes place.

tetrasporophyte: the diploid tetraspore-producing phase of the life history.

thallose: having a thallus, or thalloid organisation.

thallus: the algal body; also used in relation to other simply constructed, non-vascular plants; pl. thalli.

theca: the envelope or armour of some unicellular algae (dinoflagellates, Prasinophyceae); in diatoms, half of the two-part silica cell wall (frustule).

thecal vesicle: in dinoflagellates, a flat, polygonal, membrane-bound vesicle; vesicles form a superficial layer just beneath the plasmalemma and may be empty or contain thecal plates composed of cellulose.

thermocline: a boundary between two layers of water marked by an abrupt drop in temperature over a relatively small increase in depth.

thylakoid: a flattened, sac-like, membranous structure containing photosynthetic pigments within plastids.

thylakoid organising body: in the chloroplasts and amyloplasts of certain Bryopsidophyceae, a rounded body, consisting of concentric double membranes from which thylakoids are formed in young chloroplasts.

tier: a regular row or series (of cells).

tomentose: densely covered with short, often matted hairs.

tongue cell: a specialised initial cell formed during the development of a conceptacle.

tonoplast: a plasma membrane containing a vacuole.

torulose: cylindrical but with many rounded excrescences.

trabeculum: in Chlorophyta, a strut of cell wall material traversing and supporting the thalli of Caulerpa, or projecting inwards from the utricle wall in Codium; pl. trabeculae.

tractellum: a leading flagellum that pulls the cell behind it; cf. gubernaculum.

transapical plane: in diatoms, perpendicular to the apical axis.

transection: a cross-section of the thallus or any part of an alga.

transformation: in a parasexual process in prokaryotes, the transfer of genetic information by means of ‘naked’ extracellular DNA.

transition zone, transition region: the zone between a flagellum and its basal body, just below the basal ends of the central pair of microtubules of the axoneme; in Laminariales (Phaeophyceae), a region between the stipe and blade where active cell division is localised.

transitional helix: in many Heterokontophyta, a coiled fibre present in the transition zone between the flagellum and the basal body.

transitional plate: in dinoflagellates, a small plate located in the cingulum-sulcus junction.

transverse: across the shorter dimension of an organ or organism.

transverse flagellum: see transverse furrow.

transverse furrow: in dinoflagellates, a girdle or groove lying between the anterior and posterior ends of the cell which houses the transverse flagellum.

transversely striated connective: in flagellate cells, a transversely striated band (probably composed of the contractile protein centrin) forming part of the flagellar apparatus and connecting the basal bodies just below the insertion of the flagella.

traversing nutritive cells: in Gracilaria (Rhodophyta), elongate cells (or filaments) between the carposporophyte and pericarp, darkly staining and probably nutritive in function.

tremalith: in coccolithophorids, a calcified or potentially calcified scale rim with more-or-less vertical sides.

Triassic: the oldest geological period (213–248 Ma) of the Mesozoic Era (65–248 Ma).

tribuliform: a planar structure, almost triangular in face view, but with a small bulge or boss in the middle of the upper surface.

trichoblast: in Rhodophyta, a branched, uniseriate filament of colourless or almost colourless cells that is usually deciduous or easily broken off.

trichocyst: in Raphidophyceae and dinoflagellates, an elongate, membrane-bound organelle positioned beneath the cell surface which shoots out threads of mucilage upon stimulation of the cell.

trichocyte: in the Corallinales (Rhodophyta), a specialised (sometimes hair-producing) cell that is usually larger or has thicker walls or more deeply staining contents than other vegetative cells.

trichogyne: in Rhodophyta, the slender, hair-like extension from the carpogonium to which spermatia become attached and which conveys the male nucleus to the carpogonium.

trichome: in Cyanophyta, the filament of cells exclusive of the surrounding sheath.

trichothallic growth: in the Phaeophyceae, growth from an intercalary meristem that cuts off an apical tuft of filaments.

trichotomous: branching apically and equally in groups of three.

trichotomy: a branching that resembles a three-pronged fork.

trimorphic: with three morphological forms or phases.

tripartite hair: flagellar hair consisting of three parts: the base, shaft and terminal hair(s).

triphasic: with three phases in the life history.

triplet: see basal body.

triquetrous: a usually elongate structure, triangular in cross-section.

triseriate: consisting, wholly or in part, of three rows of cells in longitudinal series.

tristichous: with laterals in vertical rows on three radii of the axis or branch.

trophic mode: the means by which nutrition is achieved by an organism.

trophocyte: in multicellular, parasitic dinoflagellates, the single cell attaching the colony to the host.

trumpet hyphae: in Laminariales (Phaeophyceae), hypha-like filaments of cells in the medulla that are flared, like trumpets, at each cross-wall.

truncate: with the end abruptly flattened, as if cut off.

tube cell: in Characeae (Chlorophyta), a helical cell enveloping the oogonia.

tubercle: a small swelling.

tubular hair: a hollow type of proteinaceous structure constituting the shaft of the tripartite hairs found in heterokont algal flagellates.

tubulin: see microtubule.

turbinate: with the shape of a spinning top or turban.

turbulence: motion of a fluid in which irregular eddies cause mixing.

turgor pressure: the pressure exerted by a cell on its wall as a result of the tendency of the cell to take up water and swell. The greater the concentration of solutes in the cell sap, the higher is the turgor pressure at equilibrium.

tychopelagic: pertaining to an organism living a benthic existence, but entering the plankton when dislodged from its usual fixed condition.

type: the specimen on which a species (or subspecific taxon) is based; or the name that provides the basis for the next highest taxon (e.g. the type species of a genus); cf. holotype, isotype.

typification: in nomenclature, the process of designating a nomenclatural type.



ultrananoplankton: planktonic organisms less than 2 µm in size.

ultrastructure: the internal structure of cells as seen in the electron microscope.

umbilicate: depressed in the centre; navel-like.

umbo: a boss or projection in the centre of a structure.

unarmoured: in dinoflagellates, dinokont-type cells that do not have identifiable plate series and do not have apical pore complexes, although they may have an apical groove; = athecate; cf. naked.

unconsolidated: a term for a thallus that consists partly or entirely of filaments that are not appressed or pseudoparenchymatously united.

undulate: wavy.

unialgal culture: a culture containing one species or race of alga, although it may also contain bacteria.

uniaxial (construction): a thallus resulting from the primary meristematic activity of a single filament; generally recognisable by the presence of a single apical cell and a persistent central axis, although the latter is often obscured. Resulting thalli can be filamentous, parenchymatous, or pseudoparenchymatous.

unicellular: single-celled.

unilateral: with lateral branches on one side only of the axis or branch.

unilateral type of zoid architecture: in Chlorophyta, zoid architecture in which two equal flagella emerge on one side of the cell, just below the apex; the flagella are anchored in the cell by one broad, unilateral band of microtubules which, near the flagellar basal bodies, forms part of a multilayered structure (MLS).

unilocular zoidangium/zoosporangium: in Phaeophyceae, a zoidangium with one chamber, the contents of which divide, usually meiotically, into many zoids.

uninucleate: with a single nucleus per cell.

uniporate: with a single pore.

uniseriate: arranged in a single row or series of cells which is not more than one cell broad; cf. multiseriate.

unisexual: with only one sex on any one individual.

unispores: the motile spores produced by a unilocular organ.

unistratose: single-layered.

unizoids: in Phaeophyceae, the zoids formed by a unilocular zoidangium.

upwelling: movement of colder, usually nutrient-rich deeper water to the surface of oceans, usually near coastlines; driven by wind and the rotational effects of the Earth.

urceolate: shaped like an urn; hollow and contracted at the mouth.

utricle: inflated cell or terminal portion of a non-septate filament, generally forming a cortex.



vacuole: a large cavity within the cell filled with cell sap and surrounded by a plasma membrane (tonoplast).

valvar plane: in diatoms, parallel to the surface of the valves, i.e. the plane of cell division.

valve: in diatoms, one of the two major pieces of the frustule; the valves each cover one end of the cell and are separated by the girdle.

valve face: in diatoms, part of valve surrounded by mantle.

valve mantle: in diatoms, marginal part of valve, set off from the valve face at an angle.

valve view: in diatoms, the diatom cell or frustule seen with the valves in face view, i.e. at right angles to the girdle; cf. girdle view, broad, girdle view, narrow.

valvocopula: in diatoms, a band adjacent to a valve.

vaterite: in coccolithophorids, crystalline form of calcium carbonate.

vegetative cell division: cell division that results in the formation of daughter, vegetative (non-reproductive) cells.

vegetative propagation: asexual reproduction via monospores, propagules or fragmentation.

vegetative: involving cells or tissues produced by mitosis and not associated with any form of sexual reproduction.

veins: strands made up of larger cells within a (usually flattened) tissue.

velum: in diatoms, a thin, perforated layer of silica across an areola; pl. vela.

venation: the pattern produced by veins.

ventral: pertaining to the lower surface of a dorsiventral thallus; in unicellular algae, the side of the cell where subapical or median flagella are protruding.

ventral chamber: in dinoflagellates, an indentation on the ventral side of the cell at the intersection of the transverse and longitudinal furrows and from which the flagella arise.

ventral pore: in some gonyaulacoids (dinoflagellates), a pore at the junction of the first apical plate (1’) and an anterior intercalary or another apical plate.

ventral ridge: in dinoflagellates, an identifiable ridge on the right side of the sulcal intrusion onto the epitheca which structurally has a microtubular complex.

vermiculate: in dinoflagellates, plate ornamentation patterns of raised, worm-like markings in armoured species.

verrucose: covered with wart-like growths.

verticillate: structures (usually branchlets) arranged in a ring or whorl around an axis.

vesicle: generally, sac-like structure filled with gas, water, solutes or mucilage; in a cell, a small, sac-like organelle bounded by a single plasma membrane.

vesicular cell: in Rhodophyta, specialised cells functioning in secretion or storage, recognisable by their refractive contents.

vesiculate: forming a vesicle or small, sac-like structure.

voucher specimen: a herbarium specimen kept as the basis for an identification reported in the literature.



warty: verrucose; covered with wart-like protuberances.

water bloom: a massive growth of plankton, visible to the naked eye, in which the water becomes noticeably coloured (often red or green). A red water bloom in the sea is often called a red tide.

whorls: branches or structures arranged in a circle or verticel around an axis; in coccolithophorids, a crown-like appendage of arms made of modified coccoliths.

wrack: tangled mass of drift plants and algae on the seashore.



xylan: a fibrillar polysaccharide wall component in, for example, Caulerpales (Ulvophyceae), which yields xylose on hydrolysis.

xylomannan: a polysaccharide; a polymer of xylose and mannose.



zoid: a reproductive cell that bears flagella and is hence free-swimming.

zoidangium: a cell (often with a particular, characteristic morphology) in which zoids are produced; pl. zoidangia.

zonate: banding or zoning of a thallus (usually due to concentric growth); in certain Rhodophyta, parallel division of a tetrasporangium such that the four spores are arranged in a linear series.

zonation: the horizontal banding or zoning of organisms in the intertidal or subtidal regions, dependent on environmental and biotic factors.

zoochlorella: unicellular, endosymbiotic green algae that live within an animal.

zoogamete: a flagellate gamete.

zooplankton: ‘animal’ plankton; typically heterotrophic plankton.

zoosporangium: sporangium producing zoospores; pl. red tide.

zoospore: a motile reproductive cell, not involved in sexual reproduction, resulting from mitosis (mitospore) or meiosis (meiospore); = swarmer.

zooxanthella: a unicellular, endosymbiotic dinophyte (rarely a heterokontophyte) that lives within the tissues of an animal, particularly coelenterates (e.g. Symbiodinium in reefbuilding corals).

zygolith: in coccolithophorids, zygoform holococcolith having one or several bridges across the central tube.

zygote: the diploid cell resulting from gametic fusion.

zygotic meiosis: meiosis occurring during zygote maturation or germination.



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