FINE STRUCTURE OF THE SHELL OF DIPLOID AND TRIPLOID OYSTERS, CRASSOSTREA GIGAS (THUNBERG 1793) (BIVALVIA, OSTREIDAE) REARED IN THE BLACK SEA

The fine structure and chemical composition of the shell growth margin were compared in diploid and triploid oysters, Crassostrea gigas (Thunberg 1793), reared to commercial size in a Crimean marine farm. The diploid oysters were deposited from plankton, whereas the triploid ones were obtained from an Atlantic coast nursery. An electron scanning microscope SEM Hitachi U 3500 with built-in software Oxford Ultin Max 65 for microanalysis was employed in the study. The shell growth margin is shown to consist of two layers: periostracum and prismatic. The periostracum in diploid oysters is smooth and porous, whereas the periostracum of triploid oysters is volumetric and shows longitudinal folds. The prismatic layer of both right and left shell valves consists of prisms surrounded by organic membranes. In contrast to diploid oysters, triploid ones have longer prism facets, their calcite filling is significantly lower than normal, their interprismatic organic membranes are discontinuous and contain calcium carbonate. The proportion of organic matter in diploid oyster shells is significantly higher than that in triploid ones. The factors affecting the fine structure of oyster shells differing in ploidy are discussed.