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Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 50,000 species have been identified, grouped into several orders.
Ostracods are small crustaceans, typically around one mm in size, laterally compressed and protected by a bivalve-like, chitinous or calcareous shell. The hinge of the two "valves" is in the upper, dorsal region of the body.
Ecologically ostracods can be part of the zooplankton, or (most commonly) they are part of the benthos, living on or inside the upper layer of the sea floor. Some groups of ostracods are also found in fresh waters and in humid continental soils (normally in humid forests).
Ostracods are particularly useful for the biozonation of marine strata on a local or regional scale, and they are invaluable indicators of ancient shorelines, salinities and relative sea-floor depths. They have a long and well documented fossil record from the early Cambrian to the present day. An outline microfaunal zonal scheme based on both foraminifera and ostracoda was compiled by M.B. Hart (1972).
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