The circulatory system is an organ system responsible for transporting blood, nutrient s, gases, and other molecules throughout the body. The two types of circulatory systems are the open circulatory system and the closed circulatory system. The difference lies on the mode of transporting blood in the body of an animal. In open circulatory system, the blood is not confined within blood vessels. Open circulatory system is exhibited by most of the invertebrates except some like annelida, cephalopod molluscs posses closed one.