Porcellionidae is a terrestrial family of the order Isopoda. The species classified here cannot roll into a ball, as opposed to the species of family Armadillidiidae, which can. This family contains 530 species, found on every continent except Antarctica. The ventral plate of the thoracic exoskeleton flare out slightly over the legs. This "flare" is called the epimeron. The uropods, antenna-like structures at the back of the specimen, are flattened out and spearlike, and extend beyond the last exoskeletal plate.