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 vessels but instead flows freely through cavities in the body, bathing the organs directly. This allows for the exchange of nutrients and waste products between the blood and tissues. In an open circulatory system, the heart pumps hemolymph into a series of sinuses or spaces, where it circulates before returning to the heart. This system is generally less efficient than a closed circulatory system, but it requires less energy and is sufficient for the metabolic needs of smaller or less active organisms.