Histochemical and ultrastructural analyses of the epithelial cells of the body surface skin from the terrestrial slug, Incilaria fruhstorferi

Dorsal and ventral epithelium of the terrestrial slug, Incilaria fruhstorfe ri, is simple and consists of five cell types: microvillous, ciliated, roun d mucous, tubular mucous and channel. Microvillous cells were similar to hu man intestinal epithelial cells morphologically and functionally. At the ba se of microvilli, pinocytic vesicles which ultimately fused to form larger vacuoles, or multivesicular bodies were present. At the edge of tail or mou th, ciliated epithelial cells possessed the typical axonemes (9 plus 2 arra ngement of microtubles). Mucous secretory cells were either-tubular or roun d and their granules were membrane-bound and secreted by exocytosis. Granul es of round mucous cells were proteinaceous but those of tubular cells were acidic mucopolysaccharides. Channel cells were elongate U-shaped and the c entral lumen was filled with a large amount of fluid (hemolymph). The funct ion of channel cells is thought to remove hemolymph accumulated during hype rhydration. Our experiments of some markers-injection revealed that the flu id containing large molecules passed transcellularly from the hemolymph, ac ross the basal or side region of the cell and into the central lumen. These results suggest that channel cell of the slug skin and vertebrate nephron showed some parallels in structure and function.