Noun
One of the classes of the arthropods, including lobsters and crabs; -- so called from the crustlike shell with which they are covered.
Source: Webster's dictionaryAmong the procellariids, the prions concentrate on small crustacea, the fulmarine petrels take fish and krill but little squid, while the Procellaria petrels consume mainly squid. Source: Internet
Invertebrates ('animals without blood') are insects, crustacea (divided into non-shelled – cephalopods – and shelled) and testacea (molluscs). Source: Internet