Clam shrimp (once Conchostraca) are a taxon of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant, and known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in a single order Conchostraca, which later proved to be paraphyletic, being separated into three different orders: Cyclestherida, Laevicaudata, and Spinicaudata.