major fluid transport medium pumped by the heart through the body of many animal groups (including nemerteans, annelids, arthropods, molluscs, brachiopods, phoronids and chordates) carrying dissolved substances (nutrients, wastes, hormones, gases) through the body. In addition suspended specialized cells like red blood cells or erythrocytes are responsible for oxygen transport, white blood cells or phagocytes for defence against intruding organisms or harmful particles.