Anatomy:
The body of an ostracod (seed shrimp) is covered by two valves, which together form the duplicature. A distinction is made between the valve (hard parts) and the body with its appendages (delicate parts).
The body consists of a cephalon (skull), separated from the thorax by a small constriction. The segmentation is uncertain. The abdomen is regressed or absent while the adult gonads are relatively large. There are 5-8 pairs of appendages. The branchial plates are responsible for oxygenation (breathing). This is how seed shrimp breath. Read on for more information.
During the ontogeny the epidermis (containing mesodermal tissue) is invaginated ventrolaterally near the cephalon/thorax region. This invagination proceeds upwards and tailwards, until the entire animal is enveloped by lamellae on both sides: the duplicature is created. The dorsal area never becomes invaginated, and is called the isthmus. The mesodermal tissue in the duplicature develops into the vestibulum. The vestibulum makes contact with the body near the isthmus. The vestibulum plays a part in oxygenation (breathing). The two lamellae surrounding the animal each have an inner and an outer lamella.
Ostracoda is a category of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 50,000 extinct and extant species have been identified, grouped into numerous orders.
Ostracods are small crustaceans, usually around 1 mm in size, but varying between 0.2 to 30 mm, laterally compressed and sheltered by a bivalve-like, chitinous or calcareous valve or "casing". The hinge of the two valves is in the higher, dorsal area of the body.
Ecologically ostracods can be part of the zooplankton, or they are part of the benthos, living on or inside the upper layer of the sea bed. Many ostracods are also found in fresh water and some are known from humid continental woodland soils.
Fossils records:
Ostracods have a long and well-documented fossil history from the Cambrian to current day. An outline microfaunal zonal format based on both foraminifera and ostracoda was compiled by M. B. Hart (1972).
Ostracods have been particularly valuable for the biozonation of marine strata on a local or regional level, and they are invaluable indicators of paleo-environments because of their widespread occurrence, small size, easily-preservable commonly-moulted calcified bivalve carapaces, the valves are a common found microfossil.
