Any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton WordNet 3.0 & Open English WordNet

Crustaceans are animals of the subphylum Crustacea, a large, diverse group of mainly aquatic arthropods including decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, opossum shrimps, amphipods and mantis shrimp. Wikipedia

Subphylum of arthropods Wikidata

A subphylum of arthropod animals having jointed feet and mandibles, two pairs of antennae, and segmented, chitin-encased bodies. OmegaWiki

Any arthropod of the subphylum Crustacea, including lobsters, crabs, shrimp, barnacles and woodlice. Wiktionary

Arthropod of the subphylum Crustacea. Wiktionary (translation)