Clam shrimp

Clam shrimp are a group of branchiopod crustaceans that possess bivalved carapaces, which resemble the shells of unrelated bivalved molluscs. They were traditionally classified in the order Conchostraca, but this group later proved to be paraphyletic, because Diplostraca, the water fleas, are nested within the clade of clam shrimps; this implies certain groups of water fleas are closer to certain groups of clam shrimp than either are to other Diplostracan groups which they may resemble. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae. Their fossil record is known from at least the Devonian period and perhaps before.