Some members of the subphylum Crustacea are important foods for humans, such as shrimp, crab and lobster. Most species in this group are tiny aquatic species, such as water fleas and fairy shrimp, which are important components in ocean food chains. Crustaceans have two body regions; a cephalothorax and an abdomen. (Remember which other group had this division too?) They have two pair of antennae and typically at least five pair of legs. The majority of crustaceans are found in marine (saltwater) and freshwater habitats. The only widespread terrestrial crustaceans are sowbugs or pillbugs (Isopoda). Sowbugs have seven pairs of legs and some will roll into a ball when disturbed. Most are nocturnal and during the day hide in or near the soil, under bark or leaf litter or in other protected moist places. They scavenge decaying plant and animal matter; some may eat portions of living plants, and are occasionally pests in greenhouses.