Crustaceans are as abundant in the oceans as insects are on land. The majority of them are living in either marine or fresh water environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs and woodlice. Woodlice are crustaceans with a rigid, segmented, long exoskeleton and fourteen jointed limbs. They form the suborder Oniscidea within the order Isopoda, with over 3,000 known species.