Light and electron microscopic studies of hemocytes in the endemic freshwater crab Arcithelphusa cochleariformis (Brachyura: Gecarcinucidae)

The morphological and structural characterization of hemocytes was made in the endemic freshwater crab, Arcithelphusa cochleariformis using light microscopy and transmission electron microscopy and the present study provides valuable information about the cell mediated immune responses of this freshwater crab. The ultrastructural studies show four types of hemocytes: agranulocyte, granulocyte I, granulocyte II and semi-granulocyte. Agranulocytes are oval to elongate and contain free ribosomes, RER cisternae and a few mitochondria with parallel cristae. They are mostly devoid of granules but rarely a few (1-3) small granules can be observed in their cytoplasm. Our results demonstrate that the circulating agranulocytes are phagocytic in function as evident from their prominent large bulbous pseudopodial projections. Granulocytes I are round or oval in shape, possess abundant granules of differing size, shape and electron densities and their cytoplasm contains mitochondria, free ribosomes, vacuoles and lysosomes. Granulocytes II are roughly spherical or round, display RER cisternae, mitochondria and large dense granules. Certain granulocyte II cells resemble autophagosomes and include materials at various stages of degeneration and multivesicular bodies, suggesting an autophagy function. Semi-granulocytes are round, oval, elongate or irregular cells with free ribosomes, RER cisternae, mitochondria, vesicles and lysosomes. They display lysosomal compartments with phagocytized materials and melanin deposition. We here suggest their possible role in the phagocytosis and melanization process.