Class OSTRACODA Latreille, 1802

Ostracoda

© Copyright Ivana Karanovic. Western Australian Musem.

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Introduction

Ostracods are one of the most speciose groups of living Crustacea (an estimated >20,000 living species, of which approximately 8,000 have been described), and have the best fossil record of any arthropods. The oldest fossil record dates from Ordovician (Horne et al. 2002). This group of crustaceans is essentially aquatic, inhabiting both marine and non-marine environments. However, some taxa are adapted to a semi-terrestrial life, for example, living in damp leaf-litter. The majority are free living, but some are commensal on other crustaceans, echinoderms and sharks.

Diagnosis

Small crustaceans, characterised by a bivalved carapace that totally encloses the body and appendages. The body shows reduced trunk segmentation and 5–8 pair of limbs, which are protruded from the gaping valves for locomotion. They are typically 0.5–2.0 mm long in the adult stage; however, some interstitial forms are as small as 0.2 mm, some freshwater species attain 8.0 mm and the pelagic marine genus Gigantocypris reaches 32 mm.