The hemocytes of the tunicate Halocynthia roretzi are classified into six types based on their size, cellular form, and fine structure of the cytoplasmic granules: hyalinocytes, granulocytes, phagocytes, nephrocytes, morula cells, and multivacuole cells. Based on cell size, they are ordered multi-vacuole cells (7.5 μm)>nephrocytes (7.1 μm)>phagocytes (6.8 μm)>granulocytes (6.1 μm)>morula cells (5.7 μm)>hyalinocytes (5.4 μm). The proportion of hemocytes is ranked in the order multi-vacuole cells (54.8%)>nephrocytes (16.9%)>granulocytes (9.9%)>morula cells (8.8%)>phagocytes (6.1%)>hyalinocytes (3.5%).