 Bivalves have an open circulatory system that bathes the organs in hemolymph . The heart has three chambers : two auricles receiving blood from the gills , and a single ventricle . The ventricle is muscular and pumps hemolymph into the aorta , and then to the rest of the body . Some bivalves have a single aorta , but most also have a second , usually smaller , aorta serving the hind parts of the animal . 
