Class malacostraca includes crabs, shrimps, lobsters, and crayfish that have a carapace covering most of the head and trunk regions of the animals body. They have five pairs of legs, moveable stalked eyes, antennae and mandibles (jaws) for eating. Their segmented bodies allows for specialization of body sections and appendages for swimming, eating, claw crushing, and burrowing functions. They date back to the Cambrian Period (+500 million years ago).
Brooks, H. K., 1969. Malacostraca in Moore, R. C., ed., Treatise on Invertebrate Paleontology, Part R, Arthropoda 4(1), Volume 1. The University of Kansas and Geological Society of America. 398 pp.