Tumor-like lesions in the mantle of the mussel Modiolus difficilis from the Sea of Japan

Abstract

Two inner growths in the mantle beneath the epithelium were found in 1 of 1000 mussels Modiolus difficifis from Amursky Bay, Sea of Japan, within the city precincts of Vladivostok. Both growths were about 2000 pm in maximal diameter in section and elevated slightly above the mantle surface. The mantle epithelium near the growths formed deep invaginations, and clusters of mucous cells were numerous beneath the epithelium. Histological and histochemical methods were employed. Two different kinds of growth were revealed. The off-white growth consisted of cells with thin granular or vesicular cytoplasm containing glucosaminoglycans, proteins and a small amount of neutral polysaccharides. Growth cells were pure white in color after treatment of preparations with 1 % HzS04 and differed markedly from the mantle cells. The yellow growth consisted of large granular cells with neutral polysaccharides and proteins. Although growths were composed of different kinds of cells, they seemed to be derived from subepithelial mucous cells. This was supported by histological and histochemical staining reactions of some tumor and mantle epithelia1 cells. Mitotic indices (MI) of growths and subepithelial mucous cells were zero, M1 of ciliated mantle epithelium reached 0.07 %. The lesions were areas of strongly altered mucous cells of mantle epithelium and were non-neoplastic.