CYTOCHEMICAL ASPECTS OFMERCENARIA MERCENARIAHEMOCYTES

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Abstract
Hemocytes of the hard clam M. mercenaria, were examined in vitro and cytochemically stained by a variety of techniques to delineate cell types and their cytochemistry. Three cell types were identified: an agranulocyte, a small and large granulocytes. Agranulocytes with scant amount of cytoplasm, represented 2% of the hemocyte population. Small granulocytes comprised 61% of the total cell population and possessed 4 granule types. Large granulocytes accounted for 37% of all hemocytes. While they contained the same 4 granules identified in small granulocytes, only 1/3 the total number were present. The nucleus of all 3 hemocyte types appeared morphologically similar. The 4 granule types were blunt, dot-like, refractile and filamentous. Based on cytochemical staining blunt granules were identified as mitochondria. Localization of acid phosphatase in dot-like granules indicated a lysosomal function. Lipid and phospholipid staining of refractile granules indicated these granules act as lipid storage centers. Time-lapse studies revealed differential motility between hemocyte types. Small granulocytes showed greater motility than large granulocytes while agranulocytes exhibited no motility. Time-lapse cinematography also showed granulocytes to be phagocytic when exposed to yeast cells; the small granulocyte being the most active phagocyte. Nuclear similarity of the 3 cell types, similar yet graded cytochemical reactions and varying motility and phagocytic activity suggested that these cells might represent different stages of maturity rather than distinct cell lines.