An open circulatory system is a type of circulatory system found in some invertebrates, such as insects, crustaceans, and mollusks. In this system, blood, or hemolymph, is not confined to blood vessels. Instead, it flows freely through cavities in the body, bathing the organs directly. This allows for the exchange of nutrients and waste products. In an open circulatory system, the heart pumps hemolymph into the body cavity, where it circulates and eventually returns to the heart. This system is generally less efficient than a closed circulatory system, but it requires less energy and is sufficient for smaller organisms with lower metabolic demands.