Cladocera
Cla*doc"e*ra\, n. pl. [NL., fr. Gr. ? a sprout + ? a horn.] (Zo["o]l.) An order of the Entomostraca. Note: They have a bivalve shell, covering the body but not the head, and from four to six pairs of legs and two pairs of anten[ae], for use in swimming. They mostly inhabit fresh water.