An order of Entomostraca including a large number of species, most of which live in fresh water. They have flattened or leaflike legs, often very numerous, which they use in swimming. Called also Branchiopoda
. [1913 Webster
" In some, the body is covered with a bivalve shell (Holostraca); in others, as Apus, by a shield-shaped carapace (Monostraca); in others, like Artemia, there is no carapace, and the body is regularly segmented. Sometimes the group is made to include also the Cladocera."