Morphology of the Cutaneous Poison and Mucous Glands in Amphibians with Particular Emphasis on Caecilians (Siphonops annulatus).

Beatriz Mauricio,Renato Mancini Astray,Alexander Kupfer,Pedro Luiz Mailho-Fontana,Carlos Jared,Luciana Almeida Sato,Edmund D Brodie,Marta Maria Antoniazzi,Flavia Ferreira Barbosa

doi:10.3390/toxins13110779

Beatriz Mauricio, Renato Mancini Astray + Show 7 more

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https://doi.org/10.3390/toxins13110779

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Journal: Toxins	Publication Date: Nov 4, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Instituto Butantan, Utah State University

Abstract

Caecilians (order Gymnophiona) are apodan, snake-like amphibians, usually with fossorial habits, constituting one of the most unknown groups of terrestrial vertebrates. As in orders Anura (frogs, tree frogs and toads) and Caudata (salamanders and newts), the caecilian skin is rich in mucous glands, responsible for body lubrication, and poison glands, producing varied toxins used in defence against predators and microorganisms. Whereas in anurans and caudatans skin gland morphology has been well studied, caecilian poison glands remain poorly elucidated. Here we characterised the skin gland morphology of the caecilian Siphonops annulatus, emphasising the poison glands in comparison to those of anurans and salamanders. We showed that S. annulatus glands are similar to those of salamanders, consisting of several syncytial compartments full of granules composed of protein material but showing some differentiated apical compartments containing mucus. An unusual structure resembling a mucous gland is frequently observed in lateral/apical position, apparently connected to the main duct. We conclude that the morphology of skin poison glands in caecilians is more similar to salamander glands when compared to anuran glands that show a much-simplified structure.

Highlights

The skin performs, in addition to physical protection, several other vital functions such as gas exchange, ion and water transport, temperature control, chemical and mechanical sensory reception, reproduction and defence against predators and microorganisms [1,2,3,4,5]. In many of these functions, skin glands of two types located in the dermis, the mucous glands and the poison glands, which are characteristic of all amphibian orders [3,4,5], play a fundamental role [1,3,6]
Amphibians belonging to the order Gymnophiona, commonly referred to as caecilians, are vertebrates primarily adapted to a fossorial life [3]
With only 214 species [13], these animals constitute the least known group of Class Amphibia [11,14,15]. With tropical distribution, they are relatively abundant in South America, where the species Siphonops annulatus is widely distributed and adapted to different humidity levels ranging from dry regions to tropical forests [16]

Summary

Introduction

The skin performs, in addition to physical protection, several other vital functions such as gas exchange, ion and water transport, temperature control, chemical and mechanical sensory reception, reproduction and defence against predators and microorganisms [1,2,3,4,5] In many of these functions, skin glands of two types located in the dermis, the mucous glands and the poison glands, which are characteristic of all amphibian orders [3,4,5], play a fundamental role [1,3,6]. Amphibians belonging to the order Gymnophiona, commonly referred to as caecilians, are vertebrates primarily adapted to a fossorial life [3] They constitute a unique group within the class Amphibia showing, among several characteristics, a limbless and ringed body. With tropical distribution, they are relatively abundant in South America, where the species Siphonops annulatus is widely distributed and adapted to different humidity levels ranging from dry (semi-arid) regions to tropical forests [16]

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