cladocera
Cla*doc"e*ra, n. pl. Etym: [NL., fr. Gr. (Zoöl.) Defn: 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 antenæ, for use in swimming. They mostly inhabit fresh water.