The outer mantle epithelium of Haliotis tuberculata (Gastropoda Haliotidae): an ultrastructural and histochemical study using lectins

The mantle of molluscs has been the subject of many studies as it is the organ that forms the shell. Microscopic studies in particular focus on the outer mantle epithelium, but few studies address this epithelium in a histochemical way. In this study, the outer mantle epithelium in adult specimens of Haliotis tuberculata is studied, that is, in specimens involved in maintaining and repairing the shell rather than in generating it. The epithelial cells are studied by scanning (SEM) and transmission electron microscopy (TEM), and by histochemical techniques, including the use of lectins for their biochemical characterization. The epithelium is composed of pigmented epidermal cells with small microvilli and junctional complexes. It furthermore contains a few ciliated cells, as well as two types of secretory cells which differ in the ultrastructural appearance of their secretory granules and their glycoconjugate content. Histochemical study shows secretory cells containing sulphated glycoconjugates such as glycosaminoglycans or mucins rich in N-acetylgalactosamine and N-glycoproteins rich in fucose. Furthermore, the apical regions of the epidermal cells are positive for lectins that label fucose, mannose and N-acetylglucosamine. The role of epithelial cells in the synthesis of structural components of the shell is discussed.