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Tosia australis (Family Goniasteridae)

Biscuit Seastar

Distribution

Distribution:

The Biscuit Seastar ranges southern New South Wales around the southern shores to the Fremantle region of southern Western Australia, with the exception of the west -coast of Tasmania. This is a typical species of southern Australia. It may be common in some areas, especially on southern shores.

Clark (1946) states that its range extends from the Capricorn Islands in Queensland around southern shores to Fremantle, Western Australia. (NSW, TAS, VIC, SA, WA)

Features:

The Biscuit Seastar is an attractive seastar that is pentagonal (five-sided) in shape, with the plates at the end of each arm being swollen and enlarged. It differs from other seastars by having shallow arcs between the arms, forming a distinctive pentagonal shape.

The seastars' shape is quite distinctive, although there is great variation in the colour forms. Usually there are six distinctive, thickened plates along each arm radius. Other similar species have seven plates. The rest of the upper surface is covered with plates that form an interesting jigsaw pattern.

In each of the arms are two terminal (end) marginal plates that are usually larger than any other nearby plate. These are sometimes so swollen in some specimens that this morphological variation is named Tosia australis astrologorum. This form prefers wave swept shores (Edgar, 1997).

The Biscuit Seastar is a moderately small species with its radius usually 20-30 mm, but may grow to 45 mm.

The upper surface colours of the Biscuit Seastar may be greenish brown, with patches of red, pink, orange, cream, mauve, purple and black. The lower surface is normally cream, or dark grey, with some darker areas.

Ecology/Way of Life:

It may be found under rocks or in the open in the lower tidal zone and below on rocky or sandy bottoms to a depth of 10 metres. It may occur on moderately exposed reefs and sheltered shores. It may be common in some areas. It feeds on molluscs, detritus, encrusting ascidians, algae and bryozoans.

Preferred Image

Interaction with Humans/Threats:

Clark considers that the Biscuit Seastar is a typical species of southern Australia.

Further Reading:

Bennett, I. (1987). W.J. Dakin's classic study: Australian Seashores. p. 352, Angus and Robertson.

Clarke, H.L. (1946). The Echinoderm Fauna of Australia: Its composition and its Origin. Carnegie Institution of Washington, Publication: 566. pp. 567.

Davey, K. (1998). A Photographic Guide to Seashore Life of Australia. p. 128, New Holland Press.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p. 337, Reed.

Marine Research Group of Victoria. (1984). Coastal Invertebrates of Victoria: an atlas of selected species. p. 132, Museum of Victoria.

Shepherd, S.A. and Thomas, I.M. (1989). Marine Invertebrates of Southern Australia. pt. II. p. 408, South Aust. Govt. Press.

Acknowledgments:

Text, map and photograph by Keith Davey.

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Images and Multi-media:  
Attached Image  
image/jpeg 16967 bytes Biscuit Seastar
Distribution Map  
image/gif 1007 bytes Distribution of Biscuit Seastar

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