Science, Tech, Math › Animals & Nature All About the Animals Belonging to Class Asteroidea Share Flipboard Email Print Borut Furlan/WaterFrame/Getty Images Animals & Nature Marine Life Marine Life Profiles Marine Habitat Profiles Sharks Key Terms Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Forestry Dinosaurs Evolution View More By Jennifer Kennedy Marine Science Expert M.S., Resource Administration and Management, University of New Hampshire B.S., Natural Resources, Cornell University Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation. our editorial process Jennifer Kennedy Updated April 06, 2019 While the classification name, "Asteroidea," may not be familiar, the organisms it contains probably are. Asteroidea includes the sea stars, commonly called starfish. With about 1,800 known species, sea stars are a variety of sizes, colors and are a wide-ranging marine invertebrate. Description Organisms in the Class Asteroidea have several arms (usually between 5 and 40) arranged around a central disk. Asteroidea's Water Vascular System The central disk contains the madreporite, an opening that lets water into the asteroid's water vascular system. Having a water vascular system means that sea stars have no blood, but bring water in through their madreporite and move it through a series of canals, where it is then used to propel their tube feet. Classification Kingdom: AnimaliaPhylum: EchinodermataClass: Asteroidea The Asteroidea are known as the "true stars," and are in a separate class from the brittle stars, which have a more defined separation between their arms and their central disk. Habitat and Distribution Asteroidea can be found in oceans around the world, inhabiting a wide range of water depths, from the intertidal zone to the deep sea. Feeding Asteroids feed on other, usually sessile organisms such as barnacles and mussels. The crown-of-thorns starfish, however, is causing extensive damage by predation on coral reefs. The mouth of an asteroid is located on its underside. Many asteroids feed by expelling their stomach and digesting their prey outside their body. Reproduction Asteroids may reproduce sexually or asexually. There are male and female sea stars, but they are indistinguishable from one another. These animals reproduce sexually by releasing sperm or eggs into the water, which, once fertilized, become free-swimming larvae that later settle to the ocean bottom. Asteroids reproduce asexually by regeneration. It is possible for a sea star to not only regenerate an arm but also nearly its entire body if at least a portion of the sea star's central disc remains.