crustacea n class of mandibulate arthropods including: lobsters; crabs; shrimps; woodlice; barnacles; decapods; water fleas Usage(s) Outdoor food stalls display still-twitching, unnameable crustacea and old men and junkies gamble on games of Chinese chess in the concrete square outside the eponymous temple. Synonym(s) Crustacea class Crustacea