Fine structure of the abdominal epidermis of the adult mudpuppy, Necturus maculosus (Rafinesque).

The ventral epidermis of adult Necturus maculosus has been studied using electron and light microscopy. Many larval characteristics of amphibian epidermal structure are retained in adult Necturus. The epidermis is a stratified epithelium consisting of four cell layers and five cell types. Major differences compared with other adult amphibians are: the absence of a well defined moulting cycle together with an apparently diminished synthetic and mitotic activity in the stratum germinativum; an outermost cell layer (stratum mucosum) that is unkeratinized and appears to synthesize a mucous layer; and numerous large club-shaped Leydig cells which span the epidermis between the cells of the stratum germinativum and stratum mucosum. The apical region of the stratum granulosum and stratum mucosum cells shows evidence of extensive synthesis. The stratum mucosum appears to be involved in the secretion of vesicular contents onto the outermost surface of the epithelium. The external surfaces of the stratum mucosum cells possess numerous microridges which are supported by an intricate network of cytofilaments in the apical region of these cells. The significance of these features is discussed in relation to the physiology and ecology of this species.