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any member of the crustacean order Conchostraca (subclass Branchiopoda), a group of about 200 species inhabiting shallow freshwater lakes, ponds, and temporary pools throughout the world. Clam shrimps are so called because their entire body is contained within a bivalve shell (carapace) that resembles the shell of a small mollusk. Inside the shell the trunk of the animal carries up to 28 pairs of leaflike limbs that filter microscopic food particles and also assist in locomotion in those species that swim. The first two pairs of trunk limbs in the male form a claw for clasping the female during mating, hence the other common name for the group. Conchostracans are abundant in the fossil record dating back to the Silurian Period (438 to 408 million years ago).