\Crus*ta"ce*a\ (kr?s-t?"sh?-?), n. pl. [Neut. pl. of
NL. crustaceus pert. to the crust or shell, from L. crusta
the hard surfsce of a body, rind, shell.] (Zo["o]l.)
One of the classes of the arthropods, including lobsters and
crabs; -- so called from the crustlike shell with which they
are covered.
Note: The body usually consists of an anterior part, made up
      of the head and thorax combined, called the
      cephalothorax, and of a posterior jointed part called
      the abdomen, postabdomen, and (improperly) tail. They
      breathe by means of gills variously attached to some of
      the limbs or to the sides the body, according to the
      group. They are divisible into two subclasses,
      Entomostraca and Malacostraca, each of which includes
      several orders.