Sea stars feed on bivalves like clams and mussels, and other animals such as small fish, barnacles, oysters, snails and limpets. They feed by "grasping" their prey with their arms, and extruding their stomach through their mouth and outside their body, where they digest the prey. They then slide their stomach back into their body.
This image shows the underside of a sea star, and you can see it mouth (in the middle) and its tube feet.
