ostracoda

‖prop. n. pl. (Zool.) An order of Entomostraca possessing shrimplike bodies enclosed in hard bivalve shells; called also seed shrimp and mussel shrimp. They were formerly referred to as Ostracoidea. They are of small size, and swim freely about; many are less than 1 mm in length. Microfossils of certain extinct orders have been found extending back to the Cambrian age. [ 1913 Webster +PJC ]