In echinoderms, The Circulatory system is composed of thickened vessel which is also know as the heart. It lacks an endothelium which is the tissue that forms a single layer of cells lining various organs and cavities of the body, especially the blood vessels, heart, and lymphatic vessels. It is formed from the embryonic mesoderm. The echinoderms is surrounded by a pericardium; a region where ultrafiltration occurs through podocytes. It has a closed circulatory system which is different from the arthropoda and an opening to the external environment called the madreporite.