Sea stars have an open and reduced circulatory system, consisting of a central ring and five radial vessels. The water vascular system is important in the starfish because it controls the circulatory system and the movement of the sea star. Water is drawn through a small opening in the central disc and eventually passed to canals located on each arm. Also, along each canal, muscular tube feet are found on the underside of the starfish, causing the sea star to move. However, oxygen is also able to diffuse into these tube feet and into the water vascular system.