Chthonerpeton markwilkinsoni, Santos & Pineschi & Zaher, 2025

Santos, Rodolfo Otávio, Pineschi, Renato Balieiro & Zaher, Hussam, 2025, A new species of Chthonerpeton (Amphibia: Gymnophiona: Typhlonectidae) from Rio de Janeiro, Brazil, Zootaxa 5728 (3), pp. 561-570 : 562-564

Chthonerpeton markwilkinsoni sp. nov.

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( Figs. 1 , 2 , 4 ; Table 1)

Holotype. MZUSP-161064, a male specimen found in a marsh area located between the left bank of the Macacu River and the right bank of the Caceribu River ( 22°39’59.7”S 42°52’53.9”W, 4 m elevation), close to the municipality of Itaboraí, Rio de Janeiro, Brazil, collected by R. B. Pineschi on 15 January 2011.

Diagnosis. A relatively elongate species of Chthonerpeton , that differs from C. onorei and C. viviparum in having fewer primary annuli (99 versus 126–164) and vertebrae (109 versus 173–174). The new taxon differs from C. arii , C. braestrupi , and C. tremembe in having a uniformly dark-colored body (bicolored in these forms), from C. indistinctum in having more primary annuli (99 versus 72–82), from C. noctinectes in having more dentary teeth (34 versus 22–27), and from C. exile in having more premaxillary-maxillary teeth (41 versus 31). It differs further from C. perissodus in having a subtriangular and pale cloacal disk (subcircular and uniformly dark in C. perissodus ).

Description of the holotype. Morphometric and meristic data are summarized in Table 1. A well-preserved adult specimen, with a relatively elongated and narrow body shape (ratio between total length and body width equal to 27.2). Head narrower than midbody width, with the sides converging anteriorly to form a smoothly rounded snout. Eyes covered by skin, dorsolaterally oriented, and visible in lateral and dorsal views. Tentacular apertures laterally oriented and barely visible in dorsal view, slightly posterior to the anterior margin of the mouth and approximately equidistant from the eye and nostril (but slightly closer to eyes than to tentacles). Nostrils small and ovate, laterally positioned, and barely visible in dorsal view.

Mouth subterminal, with snout anteriorly projected beyond mouth. Teeth in four continuous series (i.e., without diastemas, see Table 1 for counts), all monocuspid, pointed, and recurved, with the teeth in the inner rows (i.e., vomeropalatine and inner mandibular) being slightly shorter than those in the outer tooth rows (i.e., premaxillary and maxillary). Tongue bears two anteriorly positioned and prominent narial plugs. Choanae 1.2 mm apart and about 1.3 mm in diameter. Choanal valves deeply recessed and barely visible. Collars weakly distinct and partially subdivided dorsally by faint transverse grooves.

A faint ventral transverse groove is present between the first and the second nuchal grooves. Body sub-cylindrical but slightly compressed dorsoventrally, midbody wider than anterior and posterior ends. There are 99 primary annular grooves following the collars, which incompletely encircle the body (dorsally and ventrally; none of them interrupted by the vent). Secondary annuli and scales are absent. Terminal shield present, and the body terminus is bluntly rounded. Cloacal disk small, subtriangular, with the anterior margin slightly depressed and the posterior one slightly elevated. The cloacal disk bears major sulci and shallower creases that subdivide each anal denticulation, making individual denticulations difficult to discern. We tentatively recognize five denticulations posterior and five anterior to the vent. The disk also bears two small papillae arranged slightly asymmetrically.

In life, the skin was dark gray over most of the body, with the exception of the head and the posterior tip, which were pinkish-gray. In preservative, the skin is mostly dark gray except for the eyes, tentacular aperture, cloacal disk, and a pale band overlying the lower jaw. Eyes are covered by a whitish layer of skin, which also surrounds the tentacular aperture, forming an incomplete eye-tentacle stripe. The margins of the mouth and the cloacal disk are both creamy white.

Etymology. The specific epithet is a patronym honoring Dr. Mark Wilkinson, Merit Researcher at the Natural History Museum, London ( UK), in recognition of his formidable contributions to caecilian biology, including typhlonectid systematics.

Suggested English common name. Wilkinson’s Chthonerpeton .

Figures

FIGURE 1. MZUSP-161064, the holotype of Chthonerpeton markwilkinsoni sp. nov. with head (top), whole body (middle), and body terminus (bottom). Scale bars = 1 cm.

FIGURE 2. Distribution map of the Chthonerpeton spp. (except C. braestrupi and C. exile, because both type localities remain unknown). Locality data from Nussbaum (1986), Gudynas et al. (1988), Cascon & Lima-Verde (1994), Silva et al. (2003), Maciel et al. (2013; 2015); IUCN (2024), and this study.

FIGURE 4. Morphological differences in the body terminus of the holotypes of Chthonerpeton markwilkinsoni sp. nov., MZUSP-161064 (A) and Chthonerpeton perissodus, MCZ 19972 (B). Scale bars = 5 mm.