what are crustaceans definition
The definition of a crustacean is an arthropod with a hard outer shell and jointed limbs that usually lives in aquatic environments. A lobster is an example of a crustacean.any of a subphylum (Crustacea) of arthropods, including shrimps, crabs, barnacles, and lobsters, that usually live in the water and breathe through gills: they have a hard outer shell and jointed appendages. Modern Latin Crustacea; from crustaceus, having a crust or shell; from Classical Latin crusta, crust.ny of a subphylum (Crustacea) of arthropods, including shrimps, crabs, barnacles, and lobsters, that usually live in the water and breathe through gills: they have a hard outer shell and jointed appendages.