Early Development of Caecilian Skin with Special Reference to the Epidermis

Abstract

The early developing skin of two species of caecilians, a uterine Chthonerpeton indistinctum and a free-living Ichthyophis kohtaoensis, has been described using electron microscopy. On the whole caecilian skin is typical of amphibians in its fine structure and in the Ichthyophis larva it includes most of the components recognized in premetamorphic larvae of other amphibian groups. The epidermis of Chthonerpeton, in terms of skin development relatively younger than that of Ichthyophis, has 3 types of epithelial cells and a highly microvillar surface, which may be related to its viviparity. As yet the epidermis of Chthonerpeton does not possess other cell components recognized in the better differentiated skin of the Ichthyophis larva. The presence of Merkel cells and the ultrastructure of Leydig cells, reported for the first time in the epidermis of a larval Ichthyophis, have morphological properties which conform to those already described for similar cells in other amphibian larvae. Merkel cells of Ichthyophis originate early in ontogeny and it is known that they are present in adults. Leydig cells presumably disappear at metamorphosis, as in urodeles, for they do not occur in adults. From examination of numerous specimen cells in different regions of the body of the larval Ichthyophis, it appears that Leydig cells develop from a granular type cell originating in the basal layer of the epidermis.