Any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton. Classified under: Nouns denoting animals. Hypernyms (crustacean is a kind of...): arthropod (invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin). Meronyms (parts of crustacean): green gland (one of a pair of glands (believed to have excretory functions) in some crustaceans near the base of the large antennae).