What kind of circulatory system does blood never leave the vessels?

A closed circulatory system is one in which blood never leaves the vessels. This type of circulatory system is found in all vertebrates except for fish. In a closed circulatory system, the blood is contained within a network of blood vessels, including arteries, capillaries, and veins. The heart pumps the blood through the arteries, which carry it to the capillaries, where the exchange of oxygen and carbon dioxide takes place. The blood then returns to the heart through the veins.

In contrast to a closed circulatory system, an open circulatory system is one in which the blood flows through open channels, such as sinuses and lacunae, instead of through a network of blood vessels. This type of circulatory system is found in most invertebrates, such as insects, mollusks, and crustaceans. In an open circulatory system, the blood comes into direct contact with the tissues and organs of the body.