any chiefly aquatic arthropod of the class Crustacea, typically having the body covered with a hard shell or crust, including the lobsters, shrimps, crabs, barnacles, and wood lice.
crus·ta·cean (krŭ-stā'shən) n. Any of various predominantly aquatic arthropods of the class Crustacea, including lobsters, crabs, shrimps, and barnacles, characteristically having a segmented body, a chitinous exoskeleton, and paired, jointed limbs. adj. Of or belonging to the Crustacea.
[From New Latin Crūstācea, class name, neuter pl. of crūstāceus, hard-shelled, from Latin crūsta, shell; see kreus- in Indo-European roots.]
1835, from Mod.L. Crustacea, the class name (introduced by Lamarck, 1801), neut. pl. of adj. crustaceus "having a crust or shell," from L. crusta "crust, hard shell" (see crust).