Cypris

Cypris, a very common small fresh-water crustacean, type of a family (Cypridae) in the order Ostracoda. Like other ostracods, this small 'Water-flea' (q.v.) has an unsegmented body, seven pairs of appendages, a rudimentary abdomen, and a bivalve mollusc-like shell inclosing all. The shell of cypris is dainty and elastic; the posterior antennæ bear a long tuft of bristles on their second joint; the second pair of maxillæ have a small gill-appendage; the posterior limbs are very irregular. Various species of cypris are readily found in fresh-water pools, in which they swim very actively; the largest form (C. pubera) measures 2.7 millimetres in length. The reproductive relations are of some general interest. Some species—e.g. C. fusca and C. pubera, reproduce parthenogenically in summer and autumn, the males being rare and transient; while in others—e.g. C. ovum, the males are found throughout the year, and parthenogenesis seems not to occur. The eggs are usually laid in masses on stones and water-plants; in C. pubera the egg remains as such throughout the winter. The males are remarkable for a peculiarly long and complex syringe-like modification of the reproductive duct. The adults are said to be able to survive desiccation, and this is certainly true of the eggs. Some species are very abundant as fossils in fresh-water strata—e.g. C. waldensis, in the English Wealden. See CRUSTACEA.