Mineralized dermal layer of the Brazilian tree-frog Corythomantis greeningi

Some species of anuran amphibians possess a calcified dermal layer (the Ebe rth-Kastschenko layer) located between the "stratum spongiosum" and the "st ratum compactum." This layer consists of calcium phosphate deposits, proteo glycans, and glycosaminoglycans. Although regarded as a protective layer ag ainst desiccation, a calcium reservoir, or possibly a remnant of a dermal s keleton present in anuran ancestors, very little is known about its origin, structure, and function. Thus, we studied the structure and composition of the mineralized dermal layer of Corythomantis greeningi, a peculiar hylid from the Brazilian semiarid region (caatinga), using conventional and cryos ubstitution methods combined with transmission, scanning, and analytical el ectron microscopy. Results show that the dermal layer consists of dense, cl osely juxtaposed, globular structures. Although the electron opacity of the globules was variable, depending on the type of preparation, crystal-like inclusions were present in all of them, as confirmed by dark field microsco py. Electron probe X-ray microanalysis showed calcium, phosphorus, and oxyg en, and electron diffraction revealed a crystalline structure comparable to that of a hydroxyapatite. (C) 2001 Wiley-Liss, Inc.