In closed type circulatory system, blood flows in the blood vessels. It is observed in animals belonging to annelids, cephalopod, mollusks, echinoderms and vertebrates. Blood always remain in the blood vessels, and does not come in direct contact with other cell of the body.Interconnected system of arteries, veins and capillaries are present. Exchange of nutrients and waste products between the blood and tissues via tissue fluid occurs through capillaries. The system also transports gases i.e., oxygen carbon dioxide, respiratory pigment, hemoglobin is dissolved in blood. Nucleated white blood cells are present. This is regarded as the most advanced type, having greater efficiency, maintenance of blood pressure and economy of blood volume. In earthworm there are 4 or 5 pairs of lateral side of esophagus in 7th to 13th segments. Hearts pumps the blood from the dorsal to the ventral vessel. There are three main longitudinally running blood vessels, which are interconnected through capillaries and commissural vessels.
