Isopods, Slaters and Woodlice are included in the Isopoda Order. Approximately 10,000 species of isopods have been identified. They have rigid, segmented exoskeletons and can live in fresh water, salt water and on land. Terrestrial species are called woodlice and feed on dead plant and animal matter; they are not considered predators. Aquatic species such as Isopods and Slaters feed as parasites on fish and crustaceans. When threatened, some species roll into a ball to protect themselves. Isopods play an important role in our ecosystem as they clean up the bottom of freshwater beds and rocky shorelines.