What is "cladocera"

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.

The Cladocera are an order of small crustaceans commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are long, with a down-turned head with a single median compound eye, and a carapace covering the apparently unsegmented thorax and abdomen. Most species show cyclical parthenogenesis, where asexual reproduction is occasionally supplemented by sexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.