HEMOCYTES OF THE FRESH-WATER MUSSEL, DREISSENA-POLYMORPHA PALLAS - CYTOLOGY, CYTOCHEMISTRY AND X-RAY-MICROANALYSIS

The haemocytes of Dreissena polymorpha were examined by light and elec tron microscopy. On the basis of cytology and cytochemistry, three mai n haemocyte types were identified: agranular haemocytes or hyalinocyte s, granular haemocytes represented by the neutrophilic granulocytes an d the large basophilic haemocytes (LBH). These cell types correspond t o the haemocyte classification scheme commonly established for bivalve molluscs: the granular haemocytes (granulocytes) and the nongranular haemocytes (hyalinocytes). Hydrolytic enzyme activities, such as acid phosphatase and non-specific esterases, were demonstrated within the c ytoplasmic inclusions of the neutrophilic granulocytes and the LBH. be ta glucuronidase activity was also detected in the cytoplasmic granule s and vacuoles of the LBH. Ultrastructural acid phosphatase reactivity was revealed within the matrix of the cytoplasmic granules. The prese nce of a range of hydrolytic enzymes, including hydrolases and glycosi dases in the granules, suggests that these organelles belong to the ly sosomal system. X-ray microanalysis showed the presence of P, S, Si, M g, Ca and heavy metals such as Cu, Zn, Pb and Fe in the matrix of the granules of the haemocytes in a natural population of zebra mussels. T he occurrence of trace metals sequestrated in the lysosomes suggests t he involvement of the granular haemocytes in metal accumulation, trans port and detoxication mechanisms.