Morphofunctional study of hemocytes from lions-paw scallop Nodipecten subnodosus

Hemocytes play an important role in internal defense in mollusk bivalves; they are generally divided into granular and hyaline types, where the granules possess molecules to combat foreign particles. We investigated the morphology, staining reactions, and immune-related activities of hemocytes from the pectinid lions-paw scallop Nodipecten subnodosus. We showed that, in contrast to the conditions in most bivalves and similar to other pectinids, no granular cells were observed; only very few semi-granular cells were present and the large majority of cells were hyalinocytes and blast-like cells. The cytoplasm in many hyalinocytes showed vesicles of various sizes, but none with the staining characteristics of typical granules. When hemolymph was removed from these scallops, the plasma did not clot and the hemocytes rapidly adhered to one another in suspension. When living hemocytes were placed on a glass surface, they clustered into groups of various sizes; within minutes, pseudopods extended from the cells and outward migration began. Many cells spread to form extensive networks of flat cells, and other undifferentiated cells did not spread and kept a rounded morphology. Some hemocytes were immunologically active because they phagocytize Escherichia coli bacteria. Hemocytes expressed the carbohydrates residues N-acetyl-D-glucosamine, α-D-glucose, α-D-mannose, and α-L-fucose moieties, and cytochemical assays showed activity of acid phosphatase, specific esterase, and non-specific esterase, enzymes commonly associated with lysosomes and immunologic activity. These observations serve as a useful tool for further investigation of morphofunctional studies and physiological status of scallops.