A new lungless caecilian (Amphibia: Gymnophiona) from Guyana

Abstract

We report the discovery of a single specimen of a small, terrestrial, lungless caecilian, the second known taxon of lungless caecilians. It differs from all other caecilians in lacking open external nares, and from the large aquatic lungless species described by Nussbaum & Wilkinson (Nussbaum, R. A. & Wilkinson, M. 1995 Proc. R. Soc. Lond. B 261, 331 -335) in having no significant skull modifications. All modifications are of 'soft morphology' (covered external nares and choanae, lung and pulmonary vessel loss, etc.). A new genus and species are described to accommodate this form. Aspects of its skull and visceral morphology are described and considered in terms of the possible life history and evolution of the species, and compared with those of other lungless amphibians.

Caecilita Wake & Donnelly, 2010 (Amphibia: Gymnophiona) is not lungless: implications for taxonomy and for understanding the evolution of lunglessness

“…Wake & Donnelly (2010) interpreted this species as terrestrial and as having evolved lunglessness in a terrestrial environment, which is clearly inconsistent with the RDB hypothesis providing a general explanation for the evolution of lunglessness. Wake & Donnelly (2010) saw no evidence from this instance of lunglessness to support either reduced buoyancy or energetic efficiency hypotheses for the origin of lunglessness and instead suggested that in this species its smallsize, high surface to volume ratios, a highly vascular tongue and presumed low metabolic rate may have facilitated high cutaneous respiration and ultimately loss of the lungs for reasons not yet determined.…”

“…In the field, we considered the 11 caecilians we subsequently assigned to Caecilita iwokramae to be a species of the Neotropical genus Microcaecilia Taylor, 1968 (Siphonopidae). In addition to the sealed external nares that purportedly distinguished Caecilita from all other caecilians, Wake & Donnelly (2010) stated that Caecilita differed from Microcaecilia in having an open orbit and a small vertical keel on the terminus. Judging whether the orbit is open, closed or partially open can be difficult in caecilians without probing or dissection, especially when the eye is not visible externally.…”

“…Secondary lunglessness is a rare condition that is currently considered to have evolved independently five times within amphibians, twice in caecilians, twice in salamanders and once in frogs (Hutchison, 2008;Wake & Donnelly, 2010), but nowhere else within the tetrapods. Explanations of the evolution of this unusual condition have mostly suggested that lunglessness is or was an adaptation to life in fast-flowing waters where pulmonary buoyancy, and concomitant difficulty in maintaining position, could be positively disadvantageous (e.g., Wilder & Dunn, 1920;Wilkinson & Nussbaum, 1997;Bickford et al, 2008).…”

Deciphering morphological variation in the braincase of caecilian amphibians (gymnophiona)

“…Therefore, it is difficult to predict which direction antotic morphology would tend toward as an outcome of body size reduction. Only two definitive cases of miniaturization have been documented in caecilians: 1) Idiocranium russeli (Wake,1986) and 2) Caecilita iwokramae (Wake and Donnelly,2010). Examination of the antotic region of Idiocranium russeli (97 mm) reveals the closed condition, which is a pattern that is shared with some large members of Gymnophiona, Dermophis mexicanus and Gymnopis multiplicata (each of which can reach sizes upwards of 500 mm or more, in length).…”

A new species of Rhinatrema Duméril & Bibron (Amphibia: Gymnophiona: Rhinatrematidae) from Guyana

“…The family Rhinatrematidae Nussbaum, 1977 comprises the two Neotropical genera Rhinatrema Duméril & Bibron, 1841 and Epicrionops Boulenger, 1883 and is the sister group of all other living caecilian amphibians (e.g., Wilkinson & Nussbaum 2006). Rhinatrema, hitherto known only from the type species R. bivittatum (Guérin-Méneville, 1838) itself described from a single specimen from "L'Amérique Méridionale" (Cayenne, French Guiana according to Taylor, 1968), has been considered particularly poorly known because very few additional specimens have been reported in the more than 150 years since its discovery and description. Taylor (1968) listed only two specimens, and, in the most recent revision, Nussbaum & Hoogmoed (1979) summarized variation among the four specimens of R. bivittatum known to them, including new locality records for Suriname and Guyana (although they overlooked a few additional specimens in Brazilian collections).…”