AN ULTRASTRUCTURAL-STUDY OF THE HEMOCYTES OF THE PERICARDIAL BODY IN THE ASCIDIAN CIONA-INTESTINALIS (L)

The hemocytes of the pericardial body of Ciona intestinalis were studi ed by electron microscopy. Our findings showed that stem cells, clear vesicular granulocytes, microgranulocytes, unilocular granulocytes and globular granulocytes are present at the periphery of the smaller-siz ed pericardial bodies. The stem cells are small round cells with a lar ge nucleus, with or without nucleolus, and homogeneous cytoplasm conta ining numerous ribosomes. The clear vesicular granulocytes are charact erized by an ameboid shape and cytoplasm containing several large elec tron-lucent vacuoles and small electron-dense granules. The microgranu locytes are variable in shape and contain numerous large electron-dens e granules. The unilocular granulocytes show a single large vacuole wi th an electron-dense or electron-lucent content and a thin layer of pe ripheral cytoplasm that contains the flattened nucleus. The globular g ranulocytes are characterized by the presence of large vacuoles contai ning either fibrogranular material or electron-dense aggregates. (C) 1 997 Published by Elsevier Science Ltd on behalf of The Royal Swedish A cademy of Sciences.