os·tra·cod 
(ŏstrə-kŏd′) or os·tra·code (-kōd′)
(ŏstrə-kŏd′) or os·tra·code (-kōd′)n.
Any of numerous small chiefly aquatic crustaceans of the class Ostracoda, having a bivalve carapace and including many extinct species that are commonly found as fossils.
[New Latin Ostracōda, subclass name, from Greek ostrakōdēs, testaceous, from ostrakon, shell; see ost- in the Appendix of Indo-European roots.]