Branchiopoda

Branchiopoda, a sub-order of Crustaceans in the order with leaf-like feet (Phyllopods). The name (gill-footed) refers to the fact that many of the numerous (10–40 pairs) appendages bear respiratory appendages. The body is distinctly jointed; the shell may be absent, shield-shaped, or bivalved; there are well-developed steering antennæ; the eggs are borne on several of the legs, or, in Branchipus and Artemia, in a special brood-sac. The heart is unusually elongated. They are mostly comparatively small, though not microscopic. Apus may be over 2 inches in length, and the brine-shrimp measures about half an inch. The males are less frequent, and often appear to be absent through a series of generations. The young mostly begin at the lowest level of crustacean life, known as the Nauplius (q.v.) stage, and pass through striking metamorphoses. None of the Branchiopoda are marine; a few live in salt-lakes and brine-pools; the rest in fresh water, in pools, ponds, marshes, lakes, &c. Only a few (Apus, Estheria) are known as fossils. See CRUSTACEA, BRINE-SHRIMP.