High Quality Content by WIKIPEDIA articles! Ostracods are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 65,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typically around 1 millimetre (0.04 in) in size, but varying from 0.2 millimetres (0.008 in) to 30 mm (1.2 in) in the case of Gigantocypris. Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or "shell". The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology, but the group may not be monophyletic; their molecular phylogeny remains ambiguous.