Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Cladocera, Notostraca and the Devonian Lepidocaris. They are mostly small, freshwater animals that feed on plankton and detritus, with the exception of the Cladocera, many of which are marine.
Cladocera is 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 0.2–6.0 mm (0.0079–0.24 in) long, with a down-turned head, and a carapace covering the apparently unsegmented thorax and abdomen. There is a single median compound eye. 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.