The higher division of the Crustacea, including the ordinary Crabs, Lobsters, Shrimps, &c., together with the Woodlice and Sand-hoppers.

The Malacostraca (Greek: "soft shell") are the largest subgroup of crustaceans and include most of the animals that non-experts recognise as crustaceans, including decapods (such as crabs, lobsters and shrimp), stomatopods (mantis shrimp) and krill. They also include the amphipods and the only substantial group of land-based crustaceans, the isopods (woodlice and related species). With more than 22,000 members, this group represents two thirds of all crustacean species and contains all the larger forms.