Starfish are star shaped echinoderms and belong to the class Asteroidea, which have arms that are connected to each other and their central disk ends where the arms begin. Their skin looks very spiny and they have different types of growths on the surface. Some of these bumps are used to absorb oxygen and the others are used to clean the surface of the skin.
Each starfish has hundreds of tiny feet on the bottom of each arm. These tiny feet can be filled with sea water which then fills the vascular system with water. By moving water from the vascular system into the tiny feet, the starfish can move by expanding the feet and muscles within the feet are used to retract them.