Decapoda

prop. n. pl.
  1. (Zoöl.) The order of Crustacea which includes the shrimps, lobsters, crabs, etc.
  2. (Zoöl.) A division of the dibranchiate cephalopods including the cuttlefishes and squids. See Decacera.

They have a carapace, covering and uniting the somites of the head and thorax and inclosing a gill chamber on each side, and usually have five (rarely six) pairs of legs. They are divided into two principal groups: Brachyura and Macrura. Some writers recognize a third (Anomura) intermediate between the others.