True starfish are classified in the Asteroidea, a group of echinoderms. Unlike the superficially similar brittle stars, true starfish have no sharp demarcation between arms and central body, and they move using tube feet rather than moving their whole arms. Most starfish are predators, feeding on sessile or slow-moving prey such as mollusks and barnacles. Many starfish are able to turn a portion of their stomachs out through the mouth, and thus digest food outside of the body. The majority are carnivores or scavengers and feed on invertebrates and fish. They also have powers of regeneration.