Fine structure and functions of haemerythrocytes and leucocytes of Sipunculus nudus

Abstract

The marine sipunculan worm, Sipunculus nudus Linné, possesses a voluminous coelomic cavity filled with a fluid containing different types of free cells. Most of them (more than 90%) are nucleated haemerythrocytes. They arise from free, small haemerythroblastic cells which are described in this report. Different kinds of leucocytes are also found in the coelomic fluid, particularly granulocytes which are phagocytic cells showing some similarities with vertebrate macrophages. These cells seem to arise from small hyalocytes, which are cells having morphological and physiological resemblances with vertebrate lymphocytes. It appears that the older granulocytes are progressively degranulated and give rise to large hyalocytes. Ciliary cells arising from small cells, very similar to small hyalocytes, have also been observed and it is supposed that they give rise to urn cells. Lastly, some of the biological functions of the free coelomic cells of the sipunculan worms are described.

Ultrastructure of the tentacles of Themiste lageniformis (Sipuncula)

“…They do not form the thick sheath around the nerve that Baskin (1971) described but neither are they exposed to as much stress as the polychaete ventral nerve. (Valembois and Boiledieu 1980) in most respects except that mitochondria were not seen in Themiste. Phagocytosis has been observed in sipunculan blood cells (Cuenot 1913;Chapheau 1928) and probably accounts for the vacuoles of electron dense particles in Themiste hemocytes.…”

Invertebrate Immunity: Another Viewpoint

“…The ubiquity of cell killing is evident in other reports which describe cytotoxic reactions in five different invertebrate phyla: Sipunculoidea (38,39]. Annelida [25,37], Mollusca [40].…”

“…in turn, induces a second leucocyte to kill target cells in a non-specific manner. Only the killer eells have been observed by microscopy [38]; they are small hyalocytes or granulocytes with few granules and numerous ribosomes. As seen by both electron microscopy and time-lapse microcinematography.…”

CELLULAR DEFENSE REACTIONS OFPHASCOLOSOMA AGASSIZII, A SIPUNCULAN WORM: PHAGOCYTOSIS BY GRANULOCYTES

“…Therefore, they have been used as experimental animals to investigate cellular and humoral immune reactions. In in vivo and in vitro studies, the granulocytes have been observed to be the main phagocytic cells in Sipunculus nudus (Cuenot, 1900;Cantacuzene, 1922;Volkonsky, 1933;Valembois and Boiledieu, 1980), Phascolosoma vulgare (Volkonsky, 1933), and Phascolosoma agassizii (Towle, 1962;Blitz, 1965). However, Brown and Winterbottom (1969) injected thorium dioxide into the coelomic cavity of Golfingia capensis, a species without ciliated urns, and observed that all coelomic cells ingested the thorium particles.…”