Corresponding author: Angele Martins (
Academic editor
Uwe Fritz
Threadsnakes are known for their conserved external morphology and historically controversial systematics, challenging taxonomic, biogeographic and evolutionary researches in these fields. Recent morphological studies—mostly based on µCT data of the skull and lower jaw—have resolved systematic issues within the group, for instance leading to the description of new taxa or re-positioning little-known scolecophidian taxa in the tree of life. Herein we describe a new polymorphic species of the genus
The fossorial snakes known as ‘
The threadsnakes of the family
The genus
Herein we provide the description of a new polymorphic species of the genus
We examined specimens housed in the following institutions (see Appendix
We follow
Aiming to assess the phylogenetic position of
We obtained tissue samples from 17 individuals representing five nominal and one undescribed species:
Thermocycling for DNA amplification for the first partition began with a denaturation at 94°C (5 min), followed by 40 cycles of denaturation at 94°C (30 s), annealing at 43–48°C (30 s), extension at 70°C (1 min), and a final step at 72°C after the final cycle (7 min). PCR products were visualized in 1% agarose gels and sent to Macrogen Inc. (Seoul, Republic of Korea) for purification and sequencing reactions. PCR products of
All sequences were aligned using MAFFT version 7 (
We performed partitioned Bayesian Inference (
In this study, we followed the general lineage species concept of
The authors declare that this contribution represents an original work and that no experiment was done with live animals. All specimens pertaining to
The topology recovered based on
Phylogenetic relationships of
Three-dimensional reconstruction of the skull of
Furthermore, the new species of
Adult female,
Dorsal (
Six specimens, two females (
The putative autapomorphy of
Comparative meristic data among the species of the genus
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163–285 | 245–272 | 10–13 | 3 | 10 |
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225–293 | 224–270 | 12–16 | 3–4 | 14 | |
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255–289 | 230–269 | 15–18 | 4 | 14 | This study |
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213–247 | 196–237 | 10–12 | 4 | 12 | Pinto et al. (2011); |
Adult female, Total length (TL) 186 mm, Tail length (TAL) of 8.0 mm; midbody diameter (MB) 3.2 mm; midtail diameter 2.7 mm; TL/TAL 23.2; TL/MB 5.8; rostral width 1.2 mm; inconspicuous eye spot covered by ocular scale; head length 4.9 mm, head width 2.9 mm; head subcylindrical, markedly truncate anteriorly; body subcylindrical, slightly tapered caudally near the tail; head not enlarged, indistinguishable from neck. Snout truncate in lateral and ventral views; rostral hexagonal in frontal views, and trapezoidal in ventral view; dorsal apex concave, not reaching the anterior limit of oculars; rostral contacting supranasal and infranasal laterally, and frontal dorsally; nasal completely divided horizontally by oblique suture crossing nostril; nostril roughly semicircular, positioned mostly dorsal of nasal suture; supranasal twice as high as long, contacting rostral anteriorly, infranasal ventrally, first supralabial ventrally, ocular posteriorly, and frontal dorsally; supranasal ventral boundary slightly longer than upper border of infranasal scale; infranasal twice as high as long; upper lip border formed by rostral, infranasal, anterior supralabial, ocular, and posterior supralabial scales; temporal scale not distinct in size from dorsal scales of lateral rows; two supralabials (1+1) entirely separated from each other by ocular; first supralabial about 1.5 times higher than long, not reaching the nostril level or the eye spot; second supralabial roughly semicircular, slightly longer than high, twice as high as first supralabial, its posterior margin in broad contact with temporal; ocular high, dorsal apex acuminate, anterior border straight and vertical, about 3 times higher than long, contacting posterior margins of supranasal and first supralabial anteriorly, parietal posteriorly, frontal and postfrontal dorsally; eye indistinct, covered by ocular scale; eye spot positioned in central area of expanded upper part of ocular, displaced far above nostril level; frontal subcircular, slightly wider than the other middorsal head plates (postfrontal, interparietal, and interoccipital); middorsal head plates (postfrontal, interparietal, and interoccipital) subequal in size, trapezoidal in dorsal view, weakly imbricate; frontal enlarged, about twice as wide as long, contacting rostral, supranasals, oculars, and postfrontal; postfrontal about twice as wide as long, contacting frontal, oculars, parietals, and interparietal; interparietal twice as wide as long, contacting postfrontal, parietals, occipitals, and interoccipital; interoccipital about as wide as long, contacting interparietal, occipitals, and first dorsal scale of vertebral row; parietal hexagonal, about as wide as long; lower margin contacting upper border of second supralabial, posterior margin contacting temporal, occipital, and interparietal, anterior margin in broad contact with ocular and postfrontal; occipital almost twice wider than long, its lower limit attaining level of upper margin of second supralabial, although separated from the latter by temporal; symphysial subcircular, anterior and posterior borders respectively straight and slightly convex, about twice wider than long; four infralabials; first infralabial small, subtriangular; second and third infralabials subequal, wide, somewhat higher than long, not pigmented; fourth infralabial twice longer than high high, distinctively longer than others, as high as second and third supralabial, not pigmented; dorsal scales homogeneous, cycloid, smooth, slightly imbricate, arranged in 14 scale rows around midbody and in the middle of the tail; middorsal scales 289; midventral scales 266; cloacal shield short and semicircular, almost twice as wide as long; 16 subcaudals; fused caudals absent; terminal spine indistinct or absent.
Comparisons of the head in dorsal (left column), lateral (middle column) and ventral (right column) views of the type series of
Comparisons of the tail in dorsal (left column), lateral (middle column) and ventral (right column) views of the type series of
Coloration of holotype relatively faded after preservation; dorsal, paraventral and ventral scales uniformly beige; dorsal and ventral head shields creamish white; cloacal shield creamish white.
Skull (Fig.
Three-dimensional reconstruction of the skull of
Dentary supports series of five long teeth ankylosed to inner surface of medial margin of dental concha; mental foramen nearly under fifth tooth; dorsoposterior process of dentary with rounded enlargement (n = 1), possibly to provide attachment for
Three-dimensional reconstruction of the lower jaw of
Atlas composed of neural arches, not fused dorsally or ventrally; ventral element (intercentrum I sensu
Three-dimensional reconstruction of the atlas (first to third column) and axis (fourth to sixth column) of
Composed of ilium, ischium, femur, and pubis. Ilium and pubis rod-like; ischium approximately rectangular and fused to pubis (n = 1) or ischium rod-like and not fused to pubis (n = 2*); ilium represents longest bone of pelvic girdle, being fused to pubis (n = 2*) or not (n = 1); femur approximately rectangular and curved with dorsolateral claw-like process (n = 2*) or without such process (n = 1).
Three-dimensional reconstruction of the pelvic rudiments of
Hyoid Y-shaped, extending from 8–11th (
Fully everted and almost maximally expanded hemipenis (examined ex-situ) renders a unilobed organ, about 2 mm long, slightly broadened at base, followed by a short tapered area that posteriorly expands towards apex; basal portion not ornamented on proximal half; hemipenial body with no ornamentation on either sulcate or asulcate sides; sulcus spermaticus single, entering organ on basal surface and extending toward apex of organ; sulcal folds raised and not ornamented; distal half of hemipenial body covered by three inconspicuous transverse flounces; organ apex convex and not ornamented; single and tapered projection develops from apex of asulcate side.
Schematic illustrations (upper line) and photos (lower line) of the asulcate (left) and sulcate (right) sides of the hemipenis of
Middorsal scales 285–289 (287 ± 2.8; n = 2) in females and 255–280 (269 ± 12.5; n = 4) in males; midventral scales 266–267 (266.5 ± 0.7; n = 2) in females and 230–269 (253 ± 16.4; n = 4) in males; subcaudals 15–16 (15.5 ± 0.7; n = 2) in females and 16–18 (17 ± 0.8; n = 4) in males; TL 184–204.2 (195.1 ± 12.9; n = 2) in females and 171.1–200.3 (187.1 ± 12; n = 4) in males; TL/TAL ratio 20.0–23.2 (21.6 ± 2.2; n = 2) in females and 19.4–22.5 (20.6 ± 1.5; n = 4) in males; TAL 4.3–4.9% of TL (4.6 ± 0.5; n = 2) in females and 4.4–5.1% (4.9 ± 0.3; n = 4) in males; TL/midbody diameter 2.4–3.1 (2.7 ± 0.5; n = 2) in females and 2.3–2.8 (2.6 ± 0.6; n = 4) in males; TAL/midtail diameter 2.8–3.5 (3.1 ± 0.4; n = 2) in females and 2.5–3.4 (3 ± 0.3; n = 4) in males.
Color pattern of paratypes mostly resembles that of holotype except for the following: dorsum and vent uniformly light brown in three paratypes (
Precloacal vertebrae 248–260 (254 ± 8.5; n = 2) in females and 239–263 (253 ± 10; n = 4) in males; cloacal vertebrae 4–5 (4.5 ± 0.7; n = 2) in females and 3–4 (3.5 ± 0.6; n = 4) in males; caudal vertebrae 18 in females (n = 2) and 18–20 (19.2 ± 0.9; n = 4) in males.
The specific epithet
Distribution map of
The X-ray images of two specimens (
The fossorial snakes of the Family
By contrast, other generic allocations (e.g.,
Besides the phenotypic and molecular evidence herein provided for the allocation of
The burrowing lifestyle has been repeatedly associated with phenotype conservativeness in fossorial lineages in general, including ‘
Conversely, specimens from the same locality in Brazil show a low mtDNA variation (<2%), but exhibit different snout shapes (pointed vs. not pointed). Even though recent studies (e.g.,
We provide the first hemipenial description for any of the currently known species of the genus
Finally,
The conservativeness of the external morphological characters of scolecophidians represent a challenge when trying to understand their evolution. Therefore, the combination of morphological (external and internal) and molecular data appears to be crucial in resolving systematic issues within this group. These data also reinforce the utility of osteological and hemipenial data in recognizing new taxa, especially amongst threadsnakes (
We are thankful to the following persons for allowing us to examine specimens under their care: A.L.C. Prudente (
* Specimens with one asterisk were µCT-scanned for skull comparisons.
** Specimens with double asterisk were analyzed based on dry or cleared and stained specimens
Table S1
Table S2
X-Ray Images