Histochemistry and ultrastructure of the epidermis and the subepidermal gland cells of the freshwater snails Lymnaea stagnalis and biomphalaria pfeifferi.

Abstract

The epidermis and the associated subepidermal gland cells of the freshwater snails Lymnaea stagnalis and Biomphalaria pfeifferi were studied by means of histochemical and electron microscope techniques. The single cell layered epidermis is composed of general epidermal cells, cilia cells and a few scattered goblet cells. The foot sole and the epidermal regions of the pneumostome and the ventral surface of the lips near the mouth consist nearly entirely of cilia cells; elsewhere the cilia cells are found scattered among the general epidermal cells. The apical layer of the general epidermal cells bear microvilli. Numerous mitochondria, vesicles and lysosomes are located in the apical region of the cells. Several Golgi bodies and a poorly developed granular endoplasmic reticulum occur in the supranuclear region; the nucleus lies in the basal part of the cell. The general epidermal cells in the mouth region contain numerous microfilaments compared to the general epidermal cells in the rest of the epidermis. The cilia of the cilia cells in the densely ciliated regions possess well developed roots and basal bodies interconnected by means of the basal feet. With regard to the other cell organelles, cilia cells are quite similar to the general epidermal cells. For comparison a brief study of the ultrastructure of the epidermis of the terrestrial snail Helix aspersa was carried out. The skin of the snail is covered by a mucous layer produced by various gland cells. In L. stagnalis, in addition to the epidermal goblet cells, thirteen subepidermal gland cell types could be distinguished. The histochemistry of the gland cell types is reflected in the ultrastructure. Three of the gland cell types have an ubiquitous distribution, four types are peculiar to the foot, two types to the lips and five types to the mantle. In B. pfeifferi one epidermal gland cell type and only seven subepidermal gland cell types could be distinguished. Most of these gland cells are limited in their distribution to the foot, lips and mantle edge. The observations may provide a basis for further study in the functions of the snail epidermis.