Ostracod
Ostracods, or ostracodes, are a class of the Crustacea, sometimes known as
seed shrimp. Some 70,000 species have been identified, grouped into several orders. They are small crustaceans, typically around 1 mm in size, but varying from 0.2 to 30 mm 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 region of the body. Ostracods are grouped together based on gross morphology, but the group may not be monophyletic; their molecular phylogeny remains ambiguous. Ecologically, marine ostracods can be part of the zooplankton or are part of the benthos, living on or inside the upper layer of the sea floor. Many ostracods, especially the Podocopida, are also found in fresh water, and terrestrial species of
Mesocypris are known from humid forest soils of South Africa, Australia, New Zealand, and Tasmania. They have a wide range of diets, and the group includes carnivores, herbivores, scavengers and filter feeders. As of 2008, around 2000 species and 200 genera of nonmarine ostracods are found.