Proceratophrys, Miranda-Ribeiro, 1920

O'Donohoe, M. E. Ailín, Rosset, Sergio D., Regueira, Eleonora, Haddad, Célio F. B., Basso, Néstor G. & Hermida, Gladys N., 2022, Comparative skin histology of neotropical odontophrynid frogs, Zoologischer Anzeiger 301, pp. 127-144 : 136-138

3.3. Protuberances in the genus Proceratophrys

The skin of the postorbital-supratympanic and dorsal regions of the two examined species of the genus Proceratophrys ( P. avelinoi and P. brauni ) is similar, both externally and histologically. Macroscopically, the two species show small protuberances homogeneously distributed throughout these regions ( Fig. 9A ). Microscopically, these protuberances have an epidermis consisting of 3–4 cell layers: the basal layer with cylindrical cells (stratum germinativum), a medial 1–2 layer of cubic cells (stratum intermedium), and a very thick layer of flat, highly keratinized cells (stratum corneum) ( Fig. 9B ). The epidermal surface is completely covered with conical spines ( Figs. 1C and 9C ). The latter formed by an increase in the thickness of the stratum intermedium, with superficial highly keratinized cells of the stratum corneum ( Fig. 9D ). This stratum reaches a size of 49.9–57.5 μm height and 57.2–60.3 μm width ( Table 1). Between the spines, it is possible to observe valleys where the glandular pores are located ( Fig. 9E ).

As for the dermis, the stratum compactum and stratum spongiosum are well defined and bound by the thin, discontinuous EK layer ( Fig. 9F ; Table 1). The alveolar glands have a circular pore ( Table 1), a short duct-

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neck and a secretory epithelium with cylindrical cells surrounding a broad lumen ( Fig. 9G ). The cells possess secretory granules rich in neutral glycoconjugates and proteins ( Table 2). The syncytial glands are partially clustered with connective tissue between the secretory portions ( Fig. 9F ). They have circular pores ( Fig. 9E ; Table 4) that communicate with the secretory portions through a duct-neck lined by a bistratified epithelium ( Fig. 10A ). The secretory portion consists of a broad acidophilic secretory syncytium with ovoid nuclei ( Fig. 9F ). The secretion of these glands is characterised by an acidophilic network, and basophilic and acidophilic granules ( Figs. 9F and 10B ) with neutral glycoconjugates ( Fig. 10C ), lipids and proteins ( Tables 2 and 3).

Figures

Fig. 9. Skin in species of the genus Proceratophrys. (A) External morphology of the skin showing the small protuberances that cover the body. Notice the postorbitalsupratympanic (pink-painted) and dorsal region (arrow). (B) Detail of the epidermis (ep) with its layers. (H–E). (C)–(E) Epidermal surface (eps) under SEM. Notice the pointed spines (sp) on the surface of the skin. (D) Detail of the spine. Notice the wide stratum corneum (StC) that covers the spine. (E) Circular pores can be observed between the spines (>). (F) Light microscopy image showing the arrangement of the syncytial glands (SGs) in the protuberance. (H–E). (G) Detail of the alveolar gland (AG). (A), (C), (D), (E) P. avelinoi. (B), (F), (G) P. brauni. Abbreviations: d, dermis; l, lumen of the alveolar gland; sep, secretory epithelium of the alveolar gland; sc, stratum compactum; ss, stratum spongiosum; StG, stratum germinativum; StI, stratum intermedium; arrowhead, EK layer. Scale bar: B, D, G =20 μm; C = 200 μm; E-F = 100 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 1. Morphometric parameters measured in the secretory portions (secp), glandular pores (p), and spine-like projections (sp). (A) Width (blue line) and height (red line) of pointed spine in Proceratophrys avelinoi on SEM image. (B) Major (green line) and minor (orange line) diameter of stoma-like pore of syncytial gland (SG) in Odontophrynus lavillai (SEM image). (C) Major (green line) and minor (orange line) diameter of circular pore of the alveolar gland in O. americanus (SEM image). (D) Width (blue line) and height (red line) of secretory portion of SG in O. occidentalis (Mendoza). (MMT). Abbreviations: d, dermis; ep, epidermis; eps, epidermal surface. Scale bar: A = 15 μm; B = 10 μm; C = 5 μm; D = 100 μm. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 10. Syncytial glands in species of the genus Proceratophrys. (A) Detail of the gland neck (nk). (MMT). (B) Morphology of the granules (g) and networklike secretion (ns) under SEM. (C) PAS-positive granules (g) and network-like secretion (ns). (PAS). (A), (C) P. brauni. (B) P. avelinoi. Abbreviations: secp, secretory portion; d, dermis; ep, epidermis. Scale bar: A-C = 10 μm.