The epithelia of the main organs likely to be involved in contaminant uptake, viz. mantle and gill were studied in the Asiaticclam Corbicula fluminea as a base for future ecotoxicological studies. On its margin, the mantle epithelium displays three foldsseparated by two grooves. The outer epithelium made of cubic cells, and the periostracal groove are involved in the formation iscomposed of the shell, secreting crystals and the periostracal lamella respectively. In the median area, the inner epithelium iscomposed of three cell types: ordinary epithelial cells, ciliated cells and mucocytes. The gill epithelium displays two structurallyand functionally different areas: a respiratory area in the interlamellar chamber and, on the opposite side, a ciliated epithelium.The respiratory epithelium is composed of thin pavement epithelial cells. The ciliated epithelium is made of different cell types:lateral ciliated epithelial cells, secretory cells, latero-frontal ciliated cells and ciliated frontal cells. The role of the secretory cellsis particularly discussed in relation to their structural similarity with lower vertebrate chloride cells (ionocytes) involved in iono- andosmoregulation processes.

The edge and isthmus of the mantle of Pinctada margaritifera (Mollusc, Bivalvia) were studied using light and electron microscopy from a morphological and histochemical point of view. Six areas with several subareas were differentiated in the mantle edge. One of these areas is similar to the epithelium isthmus. Trials to elucidate the nature of the pigment responsible for the black colour of the shell and pearl indicate a melanin-like material. Possible functions of the distinctive epithelial areas in Pinctada margaritifera mantle are discussed according to available data on the secretion of organic matrix of the shell, protein selerotization and deposition of crystals in some pearl-forming molluscs. Three different epithelial areas in the outer mantle edge of Pinctada margaritifera are probably involved in the sequential processes of deposition of calcite prisms, aragonite fibres and aragonite rhombs.