Having an open circulatory system, the mollusks have a pair of posterior auricles draining the gills and an anterior ventricle that pumps the blood through the anterior aorta to the tissue sinuses, excretory organs, and gills. The aorta branches, and blood is delivered into arterial sinuses, where it directly bathes the tissues. After this occurs, and all the tissues and organs have been passed through, the blood is collected by a cephalopedal sinus and is then sent back to the gills. The blood flow throughout the body is controlled by valves in the foot.