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Higher TaxaXenodermidae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Common NamesVietnamese: Ran xe dieu zug
E: Zugs’ Odd-Scaled Snake 
DistributionVietnam (Ha Giang)

Type locality: Lùng Càng Village, Minh Ngoc Commune, Bac Me District, Ha Giang Province, Vietnam, 22.7162208N, 105.1892788E (WGS 84), 228 m elevation  
TypesHolotype. IEBR 4698 (field series tag: USNM-FS 280214), adult male (Figs. 4, 5), Aryeh H. Miller, Hayden R. Davis, Anh M. Luong, and Quyen H. Do, 19 June 2019 (at night between 2000–2100 hrs). 
DiagnosisDiagnosis. 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 (Miller et al. 2020).

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 (Miller et al. 2020).

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; Teynie ́ 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 (Miller et al. 2020). 
EtymologyNamed after George R. Zug and Patricia B. Zug. 
  • Miller, Aryeh H.; Hayden R. Davis, Anh Mai Luong, Quyen Hanh Do, Cuong The Pham, Thomas Ziegler, Justin L. Lee, Kevin De Queiroz, R. Graham Reynolds, Truong Quang Nguyen 2020. Discovery of a New Species of Enigmatic Odd-Scaled Snake (Serpentes: Xenodermidae: Achalinus) from Ha Giang Province, Vietnam. Copeia 108 (4): 796-808 - get paper here
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