Achalinus zugorum, Miller & Davis & Luong & Do & Pham & Ziegler & Lee & De Queiroz & Reynolds & Nguyen, 2020

Miller, Aryeh H., Davis, Hayden R., Luong, Anh Mai, Do, Quyen Hanh, Pham, Cuong The, Ziegler, Thomas, Lee, Justin L., De Queiroz, Kevin, Reynolds, R. Graham & Nguyen, Truong Quang, 2020, Discovery of a New Species of Enigmatic Odd-Scaled Snake (Serpentes: Xenodermidae: Achalinus) from Ha Giang Province, Vietnam, Copeia 108 (4), pp. 796-808 : 800-804

Achalinus zugorum , new species urn:lsid:zoobank.org:act:1769A394-CC3C-47D3-B42E-33D2444DF3B4

Vietnamese Common Name: Rán xe điéu zug

English Common Name: Zugs’ Odd-Scaled Snake

Figures 4 , 5 ; Supplementary Figure 1 ; Supplementary Table 1

Holotype.— IEBR 4698 (field series tag: USNM-FS 280214 ), adult male ( Figs. 4 , 5 ), Lùng Càng Village , Minh Ngoc. Commune, Bac Me District, Ha Giang Province, Vietnam, 22.7162208N, 105.1892788E ( WGS 84 ), 228 m elevation, Aryeh H. Miller, Hayden R. Davis, Anh M. Luong, and Quyen H. Do, 19 June 2019 (at night between 2000–2100 hrs).

Diagnosis.— Achalinus zugorum differs from all other species of Achalinus by the following combination of morphological characteristics (Supplementary Table 1; see Data Accessibility): dorsal scales elliptical; one dorsal scale directly above each ventral scale; absence of everted labial scales; preocular absent (fused with prefrontal or loreal scale); maxillary teeth 28, all teeth curved and equal in size; internasal suture distinctly longer than that between the prefrontal suture; internasals not fused to prefrontals; loreal fused with prefrontals; seven infralabials; mental very narrow, separated from anterior chin shields; two elongated anterior temporals, in contact with eye, and two posterior temporals; dorsal scales in 25–23–23 rows, keeled; ventrals 173; subcaudals 70, unpaired; a maximum known total length of 458 mm, TailL/ TotalL ratio of 0.23; dorsum purple to jet black in life and in preservative, lower and posterior portions of head pink-gray, ventral surface iridescent and uniform black with margins of ventral scales pink-gray.

Description of the holotype.— Adult male in excellent condition, one midline incision for liver tissue extraction ( Fig. 4 ). Hemipenes partially everted. SVL 353 mm, TailL 105 mm, TotalL 458 mm, HeadL 10.9 mm, HeadW 6.0 mm, SnL 3.5 mm, SnW 2.0 mm, EyeD 1.2 mm, NarEye 2.7, InterorbD 3.7, InternasalSL length 1.9 mm, PrefrontalSL 1.3 mm, ParietalSL 5.0 mm, FrontalL 2.5 mm, FrontalW 2.8 mm, LorealL 2.0 mm, NasalAH 0.5 mm, NasalPH 0.7 mm. TailL/TotalL 0.23, HeadL/ W 0.55, SnL/HeadL 0.32, EyeD/SnL 0.35, EyeD/HeadL 0.11, FrontalW/InterorbD 0.78, InternasalSL/PrefrontalSL 1.42, FrontalL/ W 0.87, ParietalSL/FrontalL 2.0.

Body moderately elongate and subcylindrical, head oblong and slightly distinct from neck dorsally covered with large head scales ( Fig. 5 ). Scales across dorsal portion of head distinctly striated; eyes small, round with vertically subelliptical pupils; nostrils large compared to nasal scale and elliptical. Tail elongate (slightly over one-fifth of total body length), tapering to round blunt tip. Rostral scale small, subpentagonal in frontal view, barely visible from above. Posterior scale suture of rostral with internasals ‘‘gull-wing’’ shaped (broad obtuse angle). Mental scale much smaller and narrower than rostral, subrectangular. Internasals paired, rounded. Suture between internasals 1.4x longer than prefrontal suture; prefrontals paired, subrectangular, 1.7x wider than long. Frontal scale shield-shaped with weak crease along midline, 0.9x longer than wide; anterior angle formed by suture of frontal bordering prefrontals straight (1808); posterior angle formed by the sutures producing the posterior vertex of the frontal a weak obtuse angle (1008). Supraoculars rectangular, 2.1x longer than wide. Supraoculars shorter than frontal. Parietals paired, weakly subtrapezoidal, 2.5x longer than wide. Parietal suture 2.0x longer than frontal; anterior parietal angle formed by the sutures between the parietal þ frontal and the suture between the supraocular þ parietal moderately obtuse (1128) with the lateral ray of the angle pointing posterolaterally. Parietals bordered by one elongate nuchal (second row of posterior temporal) scale on each side; nuchals blocked from contacting at midline by one small scale, each scale in contact with first row of posterior temporals. Loreal scale fused with prefrontal scale; nasal scale divided below nostril, posterior portion of nasal larger than anterior. No preocular or postocular. Supralabials 6/6, first very small, contacting mental, afterwards gradually increasing in size. Supralabials 1–3 contacting nasal, 3–4 contacting fused loreal-prefrontal, 4–5 contacting orbit, 4 th in narrow contact, 5 th in broad contact, 6 th supralabial largest, 2.6x as long as 5 th supralabial, broadly subrectangular. Infralabials 7/7, first pair in contact, blocking mental from contacting anterior pair of genials; infralabials 1–3 in contact with anterior pair of genials; 1 st infralabial smallest, increasing in size until 6 th infralabial, which is the longest; the 7 th infralabial is significantly smaller than the 6 th infralabial; both scales are elongate and contact the 6 th supralabial, and is thus considered an infralabial based on this characteristic. Genial scales wider than long, subrectangular and asymmetrical. Posterior genials longer than anterior genials, right posterior genial divided into anterior and posterior scales.

Dorsal scale rows 25–23–23, all dorsal scales elliptical and distinctly keeled posterior to nape, outermost dorsal scale row slightly enlarged from innermost rows. Ventrals smooth, border with dorsal scales a broad obtuse angle. 173 ventrals with no preventrals; cloacal plate single; subcaudals 70, unpaired.

Maxillary teeth 28, anterior teeth equal in size, all curved. Mandibular and palatine teeth all equally sized and similar in shape to those of maxilla.

Hemipenes small, partially everted organ extending 5–6 subcaudal scales in length, retracted back to 2–3 subcaudal scales after preservation. Organ bilobed, semicapitate based on partial eversion; shape uniform but inflated on the sulcate side near point of lobular bifurcation. The sulcus spermaticus is forked, at centrifugal position, dividing at point of bifurcation and extending across the lobes towards the apex. Sulcus lips elevated, naked, creating large channel. The lobes of each hemipenis have not been fully prepared but are mostly naked except for a few small horizontal flounces; on the left organ, a few spinous calyces are present on the lobes; the base of the organ is somewhat flounced, without other ornamentation.

Coloration in preservative.— After formalin fixation and subsequent preservation in 70% ethanol for six months, dorsum uniform dark purple throughout entire body; dorsal portion of head same as dorsum, interstitial skin of dorsal and head scales violet-brown; medial portion of labial scales around mouth pinkish-gray; ventral region of snout dark purple, strongly iridescent; dark violet-gray along gular region; ventral ground color of body dark purple, margins of ventral scales pinkish-gray, also strongly iridescent.

Coloration in life.— The color pattern of the holotype in life is similar to the coloration after preservation. The dorsum is blackish and dark purple; interstitial skin between the dorsal scales dark gray; head same color as dorsum; underside of gular region dark brown, margins of labial scales dark brown; venter uniform jet black with the outer margins of each ventral scale dark gray, strong iridescence also present.

Etymology.— The specific epithet, a plural noun in the genitive case, honors George R. Zug and Patricia B. Zug. George is commemorated for his contributions to herpetology (reviewed by Mitchell, 2018), especially within Southeast Asia, and for his mentorship to two of the authors (AHM, JLL) and many young scientists before them. We also celebrate Patricia for her contributions to herpetology, as well as her ever endearing and compassionate spirit which continues to inspire the authors.

Distribution and natural history.— The holotype of Achalinus zugorum was collected on a small gravel road running through Lùng Càng Village, Minh Ngo. c Commune, Bac Me District, Ha Giang Province, Vietnam at an elevation of 228 meters above sea level. So far, the species is known only from the type locality and no specimens have been collected since its discovery. Nothing is known about the ecology, behavior, diet, or preferred microhabitat of this species, though it is presumably a semi-fossorial species that was drawn out by recent heavy rainfall prior to collection. The habitat surrounding its collection location consisted primarily of secondary forest with medium to small hardwoods on karst. The mean annual temperature in Ha Giang Province is 23.38C, with a dry season typically extending from October to March and the rainy season lasting April until September ( Le et al., 2007).

Comparisons.— We compare Achalinus zugorum to all other known species of snakes in the genus Achalinus and all other genera of xenodermid snakes known to inhabit Southeast Asia. Detailed comparisons between A. zugorum and other Achalinus are given in Supplementary Table 1 (see Data Accessibility). Achalinus zugorum is identified as a member of the genus Achalinus and can be differentiated from all other snakes in the family Xenodermidae inhabiting Southeast Asia by the following characters: dorsal scales elliptical (vs. cycloid in Fimbrios and Parafimbrios , raised dorsal scales present in Xenodermus ); one dorsal scale directly above each ventral scale (vs. two scales above each ventral in Parafimbrios and Xenodermus ); absence of distinctly raised and everted supralabial scale edges (vs. present in Fimbrios and Parafimbrios ); 28 maxillary teeth equal in size (vs. more than 30 teeth in Fimbrios , less than 20 teeth in Stoliczkia and Xenodermus , teeth gradually enlarging posteriorly in Parafimbrios ); dorsal scales in 25–23–23 rows (vs. greater than 25 in Fimbrios , Parafimbrios , Stoliczkia , and Xenodermus ) and additional characteristics ( Jerdon, 1870; de Rooij, 1917; Smith, 1921, 1943; Teynié et al., 2015; Ziegler et al., 2018). Achalinus zugorum can be differentiated from all other members of Achalinus except for A. formosanus chigirai , A. jinggangensis , and A. timi by the combination of the following morphological characters: loreal scale fused with the prefrontal; internasal scale not fused with prefrontal scale; internasal suture longer than prefrontal suture; 25 dorsal scale rows anteriorly; 173 ventral scales; 28 maxillary teeth; six supralabials; seven infralabials; and a uniform jet-black dorsal color pattern in life (Supplementary Table 1; see Data Accessibility).

Achalinus zugorum is differentiated from A. formosanus chigirai by having a TailL/TotalL ratio of 0.23 (vs. 0.32); 28 maxillary teeth (vs. 14); 23 dorsal scale rows at midbody and posteriorly (vs. 25–27 at midbody, 25 posteriorly); 173 ventrals (vs. 161–167 in males); 70 subcaudals (vs. 96–97 in males); 7 infralabials (vs. 5–6); and by having a dark purple or blackish dorsal coloration (vs. dark gray dorsal color pattern with darker longitudinal line along middorsum). Achalinus zugorum is differentiated from A. jinggangensis by having a TailL/TotalL ratio of 0.23 (vs. 0.17–0.22); 28 maxillary teeth (vs. 22); 173 ventrals (vs. 156–164, sex not given); 70 subcaudals (vs. 51–64, sex not given); and 7 infralabials (vs. 6). Lastly, A. zugorum is most similar morphologically to A. timi , its possible sister species, but is differentiated by having a TailL/TotalL ratio of 0.23 (vs. 0.22); 28 maxillary teeth (vs. 27); two anterior temporals contacting the eye (vs. only one contacting the eye); 23 dorsal scale rows at midbody (vs. 25); 173 ventrals with no preventrals (vs. 171 ventrals in males with one preventral); 70 subcaudals (vs. 72 in males); 7 infralabials (vs. 6); and a uniform jet black dorsal color pattern in life (vs. reddish to grayish brown dorsal color pattern, with wide portion of the vertebral region being distinctly darker). Despite the morphological differences noted above, we are unable to characterize intraspecific variation as these data are derived from a single specimen— consequently, we expect some degree of meristic and mensural variation given an ample population sample.

Conservation status.— As only a single specimen of Achalinus zugorum is thus far known, it is impossible to infer demographic parameters. However, Ha Giang Province, like much of Vietnam, is hurtling towards an increasingly ecologically fragmented and destabilized community as deforestation resulting from logging, agricultural expansion, and residential development, as well as limestone quarrying, continue to threaten the regional biota. The surrounding lowland habitat beyond the secondary forest at the type and only known locality has been heavily deforested and converted for agricultural use, thus the immediate area is seriously threatened. However, it would be inappropriate to assert that this species is a microendemic occurring only at its type locality, as many species of Achalinus are known to occur across broader geographic areas, but their secretive habits make estimating population sizes and distributions exceedingly difficult.

Odd-scaled snakes appear vulnerable to desiccation ( Pope and Granger, 1929; Ota, 2014)—a likely consequence of their non-imbricate scutellation where more interstitial skin is exposed—thus habitat modification (such as agricultural activities) could force odd-scaled snakes to drier forest edge habitats (where A. zugorum was encountered), which would represent a formidable threat to this group. Populations of A. formosanus chigirai are in decline for this reason exactly ( Ota, 2014; Zhou et al., 2017). Pope and Granger (1929) stated upon collection of A. spinalis in Fujian Province, China that the specimens were ‘‘extremely delicate’’ and that it ‘‘dries and hardens in a most unusual way’’, further signifying the importance of moist, humid forest habitats for this group.

Currently available data are inadequate to make a sound decision concerning the distribution, abundance, and population status of this species, thus we are unable to assess extinction risk. We recommend classifying Achalinus zugorum as Data Deficient (DD) under the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species criteria ( IUCN, 2020). The Data Deficient categorization is based on the paucity of data to make an appropriate classification in another Red List category, but with sufficient concern to suggest that the species is facing threats owing to development and habitat modification near the type locality.

Figures

FIG. 4. (A) Dorsal and (B) ventral views of the holotype of Achalinus zugorum, new species (IEBR 4698), after preservation. White bar ¼ 10 mm.

FIG. 5. (A, B) Lateral, (C) dorsal, and (D) ventral views of the head of the holotype (IEBR 4698) of Achalinus zugorum, new species, after preservation. Each white bar ¼ 5 mm.

FIG. 1. Ultrametric Bayesian phylogeny inferred using the COI dataset with bModelTest (Bouckaert and Drummond, 2017) in BEAST2. Posterior probabilities (PP) are provided at relevant nodes. Scale bar indicates substitutions per site. Voucher museum catalog numbers are listed adjacent to each specimen, with GenBank accessions in parentheses if no voucher numbers could be located. See Data Accessibility for tree file.