Sea stars, or starfish, are star-shaped animals that are a variety of shapes, sizes and colors. Even though they are often called starfish, sea stars are not fish. They do not have gills, fins or a skeleton. Sea stars have a tough, spiny covering and a soft underside. If you turn a live sea star over, you'll likely see its hundreds of tube feet wiggling. There are over 1,800 species of sea stars, and they come in all sizes, shapes and colors. Their most noticeable characteristic is their arms. Many sea star species have 5 arms, but some, like the sun star, can have up to 40. Sea stars feed on bivalves like clams and mussels, and other animals such as small fish, barnacles, oysters, snails and limpets. Amazingly, sea stars can regenerate lost arms.