capitalized : a large class of mostly aquatic arthropods that have a chitinous or calcareous and chitinous exoskeleton, a pair of often much modified appendages on each segment, and two pairs of antennae and that include the lobsters, shrimps, crabs, wood lice, water fleas, and barnacles

A crustacean is an invertebrate animal with a hard exoskeleton, segmented body and jointed legs. Most crustaceans are fully aquatic, although some, including many crabs, are semi-aquatic, and others, such as woodlice, are fully terrestrial (land-dwelling). There are around 80,000 known species of Crustacean.