There are some 1500 species of sea stars (also known as starfish) alive today. Sea stars, like all echinoderms, are marine animals. They inhabit all of the world's oceans and occupy a wide range of depths, from the shallows of the intertidal zone to the trenches of the abyss.
Most species of starfish have five arms (referred to as a "stellate" in their arrangement), but some groups have more than five arms (the Solasteridae for example have between 10 and 15 arms). Starfish move using many tiny tube feet located along the underside of their arms. These tube feet are part of a water vascular system in which wter is forced into the tube foot, it expands and contacts the substrate below. It then grips to the substrate, bends and water moves out of the tube foot as it is recovered for another step.
Most starfish are scavengers although some species are predators. When feeding, starfish eject their stomach out of their mouth and onto their food or prey. The food is dissolved by enzymes and then ingested as the stomach is pulled back into the body.