Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca (Crayfish, Crabs, Slaters, and Allies)

Malacostraca is the largest of the six classes of crustaceans. It contains approximately 40,000 extant species with a great diversity of body forms. They are abundant in all permanent marine and freshwater environments. Terrestrial species are found on all continental land masses as well as all tropical and temperate islands. Members of this class include crabs, lobsters, shrimp, krill and woodlice (slaters). They are segmented animals, united by a common body plan comprising of 19 to 20 body segments (rarely 21), and divided into a head, thorax, and abdomen. Malacostracans play a vitally important role in the economy. Humans consume large quantities of decapods so huge industries are involved in the capture, farming and sale of species including shrimp, lobster, and crabs which is endangering some species through commercial over-fishing. Malacostracans play a critical role role in aquatic ecosystems so their conservation is an important issue.