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Research Article
A new species of the genus Achalinus (Squamata, Xenodermatidae) from southwest Hunan Province, China
expand article infoHui Li‡, Le-Qiang Zhu‡, Bei Xiao‡, Jie Huang§, Shao-Wu Wu|, Li-Xun Yang|, Zhi-Qiang Zhang, Xiao-Yang Mo‡
‡ Hunan Normal University, Changsha, China
§ Jishou University, Jishou, China
| Forestry Bureau of Tongdao Dong Autonomous County, Huaihua, China
¶ Central South University of Forestry and Technology, Changsha, China

Corresponding author: Zhi-Qiang Zhang ( csfuzzq@126.com )

Corresponding author: Xiao-Yang Mo ( moxiaoyang@hunnu.edu.cn )

Academic editor: Robert Jadin
© 2024 Hui Li, Le-Qiang Zhu, Bei Xiao, Jie Huang, Shao-Wu Wu, Li-Xun Yang, Zhi-Qiang Zhang, Xiao-Yang Mo.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Li H, Zhu L-Q, Xiao B, Huang J, Wu S-W, Yang L-X, Zhang Z-Q, Mo X-Y (2024) A new species of the genus Achalinus (Squamata, Xenodermatidae) from southwest Hunan Province, China. ZooKeys 1189: 257-273. https://doi.org/10.3897/zookeys.1189.112784
ZooBank: urn:lsid:zoobank.org:pub:102C8154-87DF-4B55-8994-F625B8F3E46A
Open Access

Abstract

A new species of xenodermid snake, Achalinus nanshanensis H. Li, L.-Q. Zhu, Z.-Q. Zhang & X.-Y. Mo, sp. nov., is described based on three specimens collected from Nanshan National Park and Tongdao County of southwest Hunan Province. This new species is genetically distinct amongst its congeners with the mitochondrial COI uncorrected p-distance ranging from 4.4% (in A. yangdatongi) to 17.7% (in A. meiguensis). In addition, this new species can be distinguished from its congeners by a combination of the following morphological characters: (1) dorsal scales with 23 or 25 rows throughout and strongly keeled; (2) tail relatively longer so that TaL/ToL = 0.215–0.248; (3) length of suture between internasals significantly longer than that between prefrontals, LSBI/LSBP = 1.66–1.84; (4) single loreal scale present; (5) SPL 6 in number, with the fourth and fifth contacting eye; (6) IFL 6 in number, with the first three touching the first pair of chin shields; (7) TMP is 2-2-4/2-2(3)-4, with the anterior pair elongated and in contact with the eye; (8) ventrals 2 + 147–158; (9) subcaudals 64–77, unpaired; (10) dorsal body brownish black, with a bright yellow neck collar extending to the head and abdomen in the occipital region. The recognition of the new species increases the number of described Achalinus species to 28, of which 21 are found in China.

Key words

Achalinus nanshanensis sp. nov., molecular analyses, morphology, taxonomy

Introduction

Xenodermidae is composed of six known genera (Xenodermus Reinhardt, 1836, Achalinus Peters, 1869, Stoliczkia Jerdon, 1870, Fimbrios Smith, 1921, Parafimbrios Teynié, David, Lottier, Le, Vidal & Nguyen, 2015, and Paraxenodermus Deepak, Lalronunga, Lalhmingliani, Das, Narayanan, Das & Gower, 2021). The genus Achalinus is the most diverse genus of the family Xenodermidae (Uetz et al. 2022). It contains 27 recognized species and is widely distributed in eastern and southeastern Asia, where it ranges from northern Vietnam to southwestern China and partly into Japan. In the past five years, 18 species have been described in this genus (Wang et al. 2019; Ziegler et al. 2019; Li et al. 2020, 2021; Luu et al. 2020; Miller et al. 2020; Hou et al. 2021; Huang et al. 2021; Ha et al. 2022; Yang et al. 2022, 2023; Zhang et al. 2023; Ma et al. 2023a, 2023b). However, because of unresolved taxonomic problems and the poorly known distribution patterns of many species, the diversity of this genus remains underestimated.

During recent herpetological surveys in southwest Hunan, China, three Achalinus snake specimens were collected in Tongdao County and Nanshan National Park. The specimens exhibit the morphological characteristics of the genus Achalinus, which include a small, elongated, cylindrical body; strongly keeled, lanceolate scales with a metallic luster; and the lack of preocular and postocular scales, featuring a single loreal scale and temporals that are in direct contact with the eyes (Peters, 1869; Zhao et al. 1998; Zhao, 2006), but they could not be assigned to any known species. Extensive morphological examinations and further molecular analyses revealed that these specimens represent a separately evolving lineage within the genus Achalinus and can be distinguished from recognized congeners. We herein describe this overlooked Achalinus population as a new species, based on an iterative taxonomic approach.

Materials and methods

Sampling

Three odd-scaled snake specimens were collected in Hunan Province, China: two specimens (HNNU230902, HNNU230903) were collected in Nanshan National Park, and one specimen (HNNU230901) was collected in Tongdao County (Fig. 1). The three specimens were collected in the field, fixed in 75% ethanol, and deposited in the Vertebrate Zoology Laboratory, College of Life Science, Hunan Normal University. For molecular analyses, 33 sequences were used, among which 30 (sequences 4–33 in Table 1) were obtained from GenBank which include 27 sequences of 23 Achalinus species. Additionally, sequences of Fimbrios klossi, Smith, 1921, Parafimbrios lao, Teynié, David, Lottier, Le, Vidal & Nguyen, 2015 and Xenodermus javanicus, Reinhardt, 1836 were used as outgroups. Details are shown in Table 1.

Table 1.
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Localities, voucher information, COI GenBank accession numbers, and references for all samples used in this study.

No. Species Voucher Locality GenBank References
1 A. nanshanensis sp. nov. HNNU230901 Tongao, Huaihua, Hunan, China OR523368 This study
2 A. nanshanensis sp. nov. HNNU230902 Nanshan National Park, Hunan, China OR523369 This study
3 A. nanshanensis sp. nov. HNNU230903 Nanshan National Park, Hunan, China OR523370 This study
4 A. ater SYSr00852 Huaping Nature Reserve, Guangxi, China MN380334 Wang et al. 2019
5 A. dabieshanensis AHU2018EE0710 Fuziling Provincial Reserve, Anhui, China MW316598 Zhang et al. 2023
6 A. damingensis ANU20220009 Shanglin, Nanning, Guangxi, China OP644487 Ynang et al. 2023
7 A. dehuaensis YBU13013 Dehua, Fujian, China MZ442642 Li et al. 2021
8 A. emilyae IEBR4465 HoanhBo, Quang Ninh, Vietnam MK330857 Ziegler et al. 2019
9 A. formosanus RN2002 Taiwan, China KU529452 Unpublished
10 A. huangjietangi HSR18030 Huangshan, Anhui, China MT380191 Huang et al. 2021
11 A. hunanensis CIB119039 Huaihua, Hunan, China OQ848425 Ma et al. 2023
12 A. hunanensis CIB119040 Ningxiang, Hunan, China OQ848426 Ma et al. 2023
13 A. juliani IEBRA.2018.8 HaLang, Cao Bang, Vietnam MK330854 Ziegler et al. 2019
14 A. meiguensis GP835 Mianyang, Sichuan, China MZ442641 Li et al. 2021
15 A. niger RN0667 Taiwan, China KU529433 Unpublished
16 A. ningshanensis ANU20220006 Ningshan, Shaanxi, China ON548422 Yang et al. 2022
17 A. ningshanensis ANU20220007 Ningshan, Shaanxi, China ON548423 Yang et al. 2022
18 A. panzhihuaensis KIZ040189 Yanbian, Sichuan, China MW664862 Hou et al. 2021
19 A. pingbianensis YBU18273 Honghe, Yunnan, China MT365521 Li et al. 2020
20 A. quangi sp4 northern Vietnam OQ197471 Anh et al. 2023
21 A. rufescens SYSr001866 Hongkong, China MN380339 Wang et al. 2019
22 A. spinalis SYSr001327 Badagong Mountains, Hunan, China MN380340 Wang et al. 2019
23 A. timi IEBRA.2018.10 ThuanChau, Son La, Vietnam MK330856 Ziegler et al. 2019
24 A. tranganensis VNUFR.2018.21 NinhBinh, Vietnam MW023086 Luu et al. 2020
25 A. vanhoensis VNUFR.2019.13 VanHo, Son La, Vietnam ON677935 Ha et al. 2022
26 A. yangdatongi KIZ034327 Wenshan Nature Reserve, Yunnan, China MW664865 Hou et al. 2021
27 A. yangdatongi YPX51447 Xichou county, Yunnan, China MW664864 Xu et al, 2023
28 A. yangdatongi YPX51446 Xichou county, Yunnan, China MW664863 Xu et al, 2023
29 A. yunkaiensis SYSr001443 Dawuling Forestry Station, Guangdong, China MN380329 Wang et al. 2019
30 A. zugorum IEBR4698 Bac Me, Ha Giang, Vietnam MT502775 Miller et al. 2020
31 Fimbrios klossi IEBR3275 Quang Ngai, Vietnam KP410744 Teynié et al. 2015
32 Parafimbrios lao MNHN2013.1002 Louangphabang, Laos KP410746 Teynié et al. 2015
33 Xenodermus javanicus – Sumatera Barat, Indonesia KP410747 Teynié et al. 2015
Figure 1. 

Distribution of some species of the genus Achalinus, Red star: the type locality of A. nanshanensis sp. nov. (HNNU230902, HNNU230903): Nanshan Nation Park, Shaoyang City, Hunan Province, China; A. nanshanensis sp. nov. (HNNU230901): Tongdao County, Huaihua City, Hunan Province, China. Blue triangle: the type locality of A. yangdatongi in Xichou County, Yunnan Province; Black circle: the type locality of A. damingensis in Shanglin County, Guangxi Province. Purple diamond: the type locality of A. hunanensis in Hecheng District and Ningxiang County, Hunan Province.

Morphological examination

Morphological descriptions follow Zhao (2006). Abbreviations in this study are as follows: ,snout–vent length (SVL, length from tip of snout to anterior margin of the cloaca); ,tail length (TaL, length from posterior margin of cloaca to tip of tail); ,total length (ToL, length from snout tip to tail end; ,head length (HL, length from the tip of snout to the posterior margin of mandible; ,head width (HW, width from the widest part of the head in dorsal view); ,eye diameter (ED, diameter from the most anterior corner of the eye to the most posterior corner); ,loreal height (LorH, height from the highest part to the lowest part of the loreal in lateral view); ,loreal length (LorL, length from the most anterior loreal to the most posterior loreal in lateral view); ,length of the suture between internasals (LSBI); ,length of the suture between prefrontals (LSBP). Three characters were measured with a ruler to the nearest 1 mm: SVL, TaL, and ToL; other measurements were measured used digital calipers to the nearest 0.1 mm.

The scale features and their abbreviations are as follows: ,loreals (Lor); ,supralabials (SPL); ,infralabials (IFL); ,number of chin shield pairs (Chins); infralabials touching the first pair of chin shields (IFL-1st Chin); ,postoculars (PtO); ,temporals (TMP); ,supraoculars (SPO); ,temporals (TEM), ,number of anterior temporals that touch the eye (aTEM-Eye) (head bilateral scale counts are given as left/right), ,pre-ventral scales (PrV), ,ventral scales (VEN), ,subcaudal (SC), ,entire or divided state of the anal scales (Anal), ,dorsal scale rows (DSR) (counted at one-head-length behind the head, at midbody, and at one-head-length before the anal); ,the number of maxillary teeth (MT). We also make comparisons with other species of the genus Achalinus based on available literature (Peters 1869; Boulenger 1888, 1908; Van 1912; Pope 1935; Bourret 1937; Hu and Zhao 1966; Hu et al. 1975; Zong and Ma 1983; Ota and Toyama 1989; Zhao et al. 1998; Zhao 2006; Wang et al. 2019; Ziegler et al. 2019; Li et al. 2020; Luu et al. 2020; Miller et al. 2020; Hou et al. 2021; Huang et al. 2021; Ha et al. 2022; Yang et al. 2022, 2023; Ma et al. 2023a, 2023b; Xu et al. 2023; Zhang et al. 2023). The sex was determined by the presence/absence of everted hemipenes.

Phylogenetic analyses

Genomic DNA was extracted from preserved liver tissue using the TIANamp Genomic DNA Kit. The fragment of the mitochondrial DNA gene encoding cytochrome c oxidase subunit I (COI) was amplified using the primer pairs Chfm4 and Chrm4 (Che et al. 2012). The polymerase chain reaction (PCR) was performed in 20 μL of reactant with the following cycling conditions: 95 °C for 4 min, 35 cycles of denaturing at 94 °C for 40 s, annealing at 53 °C for 40 s, and extending at 72 °C for 1 min, and a final extending step of 72 °C for 10 min. The PCR products were sequenced at Shanghai Map Biotech Co., Ltd.

The COI sequences (629 bp) were assembled using SeqMan in the DNASTAR software package (Burland 2000), and compared and aligned using MEGA 7 software (Kumar et al. 2018). The uncorrected pairwise distances (p-distance) were calculated in MEGA 7. MrBayes 3.2.4 (Ronquist et al. 2012) was used to conduct the Bayesian inference analysis under the best-fitting model GTR + I + G4, which was selected by ModelFinder identified via AICc (Darriba et al. 2012). A maximum-likelihood analysis (Nguyen et al. 2015) was executed using IQ-TREE 2 under the best-fit model TIM3 + F + I + G4 selected by Modelfinder according to AICc.

Results

Molecular analyses

The maximum-likelihood (ML) and Bayesian-inference (BI) analyses resulted in essentially identical topologies, which are integrated in Fig. 2 with the distances given in Table 2. The new species is nested within the genus Achalinus, and its affinity to A. yangdatongi, A. damingensis, A. ningshanensis, and A. hunanensis considerably strong supported (BI, PP = 0.85; ML, BS = 93%). In addition, the p-distance among all species within the genus ranges from 4.4–17.7% (Table 2), the minimum genetic distance between the new species and its congers is greater than the lowest one (3.2–3.4% between A. ningshanensis and A. hunanensis). Given that the Achalinus populations from Tongdao County and Nanshan National Park possess significant morphological differences from all known congeners, we describe it as a new species below.

Table 2.
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Uncorrected p-distances (%) among Achalinus species inferred from mitochndrial COI gene.

1–3 4 5 6 7 8 9 10 11–12 13 14 15 16–17 18 19 20 21 22 23 24 25 26–28 29
1–3 A. nanshanensis sp. nov. 0–0.5
4 A. ater 6.7–6.9
5 A. dabieshanensis 16.0 14.7
6 A. damingensis 5.3–5.8 8.2 15.8
7 A. dehuaensis 14.3–14.6 16.5 18.4 16.0
8 A. emilyae 12.8–13.0 11.7 17.7 13.0 15.5
9 A. formosanus 14.4–14.9 14.1 19.0 14.9 15.9 13.9
10 A. huangjietangi 16.6 15.0 8.9 16.3 16.5 14.5 15.6
11–12 A. hunanensis 4.7–5.6 7.1–7.3 16.9–17.1 6.1–6.3 14.9–15.3 13.0–13.2 13.7–14.0 16.8 0.5
13 A. juliani 7.7–7.9 7.1 15.8 8.5 14.9 12.3 12.5 14.6 8.7–8.8
14 A. meiguensis 17.7 15.4 17.7 16.8 18.1 15.4 15.6 15.2 16.4 16.8
15 A. niger 12.8–13.3 13.5 15.8 14.3 15.9 12.2 9.1 13.9 13.2–13.3 12.3 13.9
16–17 A. ningshanensis 5.1–5.6 7.6–7.7 17.1–17.2 7.2–7.8 16.3–16.5 13.5–14.1 14.8–15.1 17.2 3.2–3.4 9.1–9.6 17.0 14.6 0.7
18 A. panzhihuaensis 15.1–15.5 16.2 16.6 15.5 15.3 16.6 16.0 15.2 16.2 15.5 11.6 14.4 17.1–17.4
19 A. pingbianensis 11.6–11.8 11.8 15.3 11.3 14.9 12.9 14.6 13.0 11.1 12.1 16.8 11.8 11.7–12.4 14.9
20 A. quangi 12.8–13.1 11.7 18.1 13.1 15.4 3.5 13.9 15.0 13.2 12.7 15.2 13.4 12.8–13.4 16.9 13.9
21 A. rufescens 11.9–12.0 12.7 16.9 13.8 14.3 8.0 14.1 14.3 12.1 12.3 17.3 12.3 12.3–12.7 16.0 12.9 7.9
22 A. spinalis 13.9–14.1 15.2 16.6 15.1 14.3 13.9 13.9 13.4 13.9 13.9 16.0 15.6 15.1–15.6 15.8 13.3 13.9 13.0
23 A. timi 13.6–13.8 13.3 16.4 13.5 16.0 13.1 13.8 14.8 12.0 14.1 15.8 13.6 13.6 15.5 12.3 13.6 13.9 14.3
24 A. tranganensis 13.0–13.1 12.7 15.3 13.9 13.9 11.5 16.8 13.4 14.0 13.3 16.4 15.2 14.3–15.2 16.4 13.3 12.2 11.5 14.6 13.8
25 A. vanhoensis 12.4–12.8 13.1 15.5 12.6 16.0 12.2 14.0 14.6 11.5 13.6 15.6 12.1 12.1–12.4 15.5 10.8 12.4 13.8 12.9 5.2 13.3
26–28 A. yangdatongi 4.4 6.2 16.6 5.6 14.0 12.8 14.4 14.6 5.1 7.3 17.1 5.9 5.8–5.9 15.5 11.3 12.6 11.5 14.2 13.1 12.8 11.3
29 A. yunkaiensis 12.5–12.8 12.8 14.9 12.5 14.7 13.1 12.3 12.5 12.0 12.5 15.8 13.7 13.0–13.7 15.7 11.6 13.6 13.3 12.0 14.1 13.5 13.6 12.0
30 A. zugorum 12.8–13.0 13.1 15.3 12.8 14.3 12.3 13.1 14.3 11.8 13.1 15.0 12.8 12.8 15.3 11.0 12.7 13.5 13.3 13.6 11.9 11.9 12.2 10.9
Figure 2. 

Phylogenetic tree of the genus Achalinus inferred from CO1 gene fragments (629 bp) by maximum-likelihood analysis. The numbers above the branches represent the supporting values: SH-like approximate likelihood ratio test and Bayesian posterior probabilities (the ones lower than 50 are displayed as “-”). Achalinus nanshanensis sp. nov. is highlighted in blue and A. yangdatongi in yellow.

Taxonomic account

Achalinus nanshanensis H. Li, L.-Q. Zhu, Z.-Q. Zhang & X.-Y. Mo, sp. nov.

https://zoobank.org/353AD101-0B8D-4C85-88FE-0E0C63120051
Fig. 3, Table 3

Type materials

Holotype : China • adult ♂; Hunan Province, Shaoyang City, Chengbu County, Nanshan National Park; 26°11′46.34″N, 110°07′56.38″E, alt. 1665 m; 1 Sept. 2023; Hui Li & Leqiang Zhu leg.; HNNU230903. Paratypes: China • 1 adult ♂; Hunan Province, Huaihua City, Tongdao County; 25°54′42.37″N, 109°44′31.39″E; alt. 300 m; 14 Oct. 2022; Shaowu Wu & Lixun Yang leg.; HNNU230901 • 1 adult ♂; same locality and date as holotype; HNNU230902.

Figure 3. 

General view of Achalinus nanshanensis sp. nov. (HNNU230902) in life. Photo by Le-Qiang Zhu.

Etymology

The new species is named for on its type locality. We suggest the Chinese common name 南山脊蛇 (pin yin: Nán Shān Jǐ Shé) and the English common name Nanshan odd-scaled snake.

Table 3.
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Main morphological characters of Achalinus nanshanensis sp. nov.

Voucher
HNNU230903 HNNU230901 HNNU230902
Holotype Paratype Paratype
Sex Adult male Adult male Adult male
SVL 362 302 300
TaL 99 99 99
TL 461 401 399
TaL/TL 0.215 0.247 0.248
HL 10.95 10.07 10.18
HW 7.25 5.96 6.37
ED 1.11 1.10 1.09
SPL 6/6 6/6 6/6
SPL-Eye 4th–5th 4th–5th 4th–5th
IFL 6 6 6
Chin 2 2 2
IFL-1stChin 1st–3rd 1st–3rd 1st–3rd
SPO 1 1 1
LorH 0.83 0.77 0.72
LorL 1.86 1.45 1.46
LorH / LorL 0.47 0.53 0.49
LSBI 1.78 1.52 1.49
LSBP 1.07 0.86 0.81
LSBI / LSBP 1.66 1.76 1.84
TEM 2+2+4 2+2+4 2+2(rarely 3)+4
aTEM-Eye 2 2 2
DSR 23-23-23 23-23-23 25-25-25
VEN 155 158 147
SC 64 77 72
Anal 1 1 1

Diagnosis

The new species can be distinguished from other members of Achalinus by the following characteristics: (1) dorsal scales with 23 or 25 rows throughout and strongly keeled; (2) tail relatively longer so that TaL/ToL = 0.215–0.248; (3) length of suture between internasals significantly longer than that between prefrontals, LSBI/LSBP = 1.66–1.84; (4) single loreal scale present; (5) SPL 6 in number, with the fourth and fifth contacting eye; (6) IFL 6 in number, with the first three touching the first pair of chin shields; (7) TMP is 2-2-4/2-2(3)-4, with the anterior pair elongated and in contact with the eye; (8) ventrals 2 + 147–158; (9) subcaudals 64–77, unpaired; (10) dorsal body brownish black with a bright-yellow neck collar extending to the head and abdomen in the occipital region.

Description of holotype

Adult male with a total length of 461 mm (SVL 362 mm and TaL 99 mm), tail relatively long, TaL/ToL 0.215, body slender and cylindrical. Head distinct from neck, rostral small, triangular, only upper tip visible from above. Head length 10.95 mm, head width 7.25 mm. Length of suture between internasals much longer than that between prefrontals (LSBI 1.78 mm, LSBP 1.07 mm, LSBI/LSBP 1.66). Frontal pentagonal pointed backwards, much shorter than parietals; each parietal bordered with an elongated nuchal, with no preoculars and postoculars. Nostril at anterior part of nasal scale, posterior margin of nostril with a distinct nostril cleft. A single loreal scale present, extending from nasal scale to eye, distinctly wider than high. Eyes small, ED 1.11 mm. Two aTMP and four pTMP present; aTMPs elongated, upper one much smaller than the lower one; upper one in contact with eye, lower one also in contact with parietal scale. SPL 6 in number, the fourth and fifth in contact with the eye, the sixth longest. Two pairs of shields present, the first three in contact with first chin shield. One mental scale present, the first IFL in contact with each other after the mental scale, followed by another 5 IFL in contact with each other. Dorsal scales 23-23-23, strongly keeled; dorsum with no longitudinal vertebral stripe. VEN 155 in number. SC 64 in number, uniserial, anal entire.

Coloration of holotype in life

Scales possess a subtle iridescent quality. The dorsum’s distinguishing characteristic is its reflective, brownish-black appearance, with a notable bright-yellow patch that extends to the head and abdomen in the occipital region. The first pair of chin shields displays black coloration at the front, while the second pair is entirely white. The eyes are uniformly black. The ventral side is prevalently grayish white, with the edges of the ventral scales gradually transitioning from grayish white to black. The ventral coloration of the tail mirrors that of the dorsum, featuring a brownish-black hue.

Coloration in preservative

(Figs 4, 5) All scales retain a subtle iridescence. The coloration darkens as it transitions from the dorsum to the venter, with the dorsal surface of the body primarily appearing brownish black. Notably, the collar of the neck is a paler grayish white.

Figure 4. 

The view of Achalinus nanshanensis sp. nov. A HNNU230903 (holotype) B HNNU230902 (paratype) C HNNU230901 (paratype), remaining photos by Le-Qiang Zhu.

Figure 5. 

Holotype of Achalinus nanshanensis sp. nov. (HNNU230903) in preservative A dorsal view B ventral view. Photos by Hui Li.

Distribution and habits

(Fig. 6) Achalinus nanshanensis sp. nov. is currently known from Hunan Province, China, and specifically from Nashan National Park, Shaoyang City, and Tongdao County in Huaihua City. It has a known elevational range of 300–1665 m above sea level. All three specimens were found during the night, with the holotype and one paratype found near a mountain stream where the air temperature was 18 °C and the relative humidity was 80%. These individuals were close to shrubs in a subtropical broadleaved evergreen forest. They were found making their way from leaf litter to the stream. The other specimen was found in a bamboo forest near a steam.

Figure 6. 

Habitat of Achalinus nanshanensis sp. nov. (HNNU230902, HNNU230903), Nanshan National Park, Chengbu County, Shaoyang City, Hunan Province, China. Photo by Le-Qiang Zhu.

Comparison

A summary of morphological characteristics is listed in Table 4. Phylogenetically, A. nanshanensis sp. nov. is closest to A. yangdatongi Hou, Wang, Guo, Chen, Yuan & Che, 2021 and A. damingensis Xu, Yang, Wu, Gong, Huang & Huang, 2023. However, A. nanshanensis sp. nov. differs from A. yangdatongi in having fewer ventral scales (147–158 vs 155–177), maxillary teeth (18 vs 24–26) and more temporals (2+2/3+4 vs 2+2/3+2/3), shorter loreal (0.47–0.53 vs 0.57) (Table 5). The new species differs from A. damingensis in having more temporals (2-2/3-4 vs 2-2-3) and fewer ventral scales (147–158 vs 165).

Table 4.
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A morphological comparison of male species of the genus Achalinus. Morphological data of examined congeners were taken from the literature. “–” & “?” = unavailable, “*” = female species (sevral species of genus Achalinus recorded only female samples).

Species TaL/ToL MT LorH/LorL LSBI vs. LSBP DSR Lor PtO SPL SPL-Eye IFL IFL-1st Chin TEM aTEM-Eye VEN SC
nanshanensis sp. nov. 0.215–0.248 18 0.47–0.53 >1 (23–25)-(23–25)-(23–25) 1 0 6 4–5 6 1–3 2+2+4/2+2(3)+4 2 147–158 64–77
A. ater 0.190 ~ 0.220 – 0.40 > 1 (21–23)-(21–25)-(21–25) 1 0 6 4–5 5–6 1–3 2+2+3 2 146–164 50–66
A. dabieshanensis 0.177 ~ 0.223 – 0.73 ~ 0.81 < 1 23-23-23 1 0 6 4–5 5 1–3 2+2+4 2 141–151 46–55
damingensis 427 – – >1 23-23-23 1 0 6 4–5 6 1–3 2+2+3 2 165 74
A. dehuaensis 0.262 ~ 0.286 31–33 – > 1 23-23-23 1 0 6 4–5 5 1–3 2+2(3)+3(4) 1–2 142–143 74–81
A. emilyae* 0.183 ~ 0.203 27–28 – > 1 23-23-23 1 0 6 4–5 5 1–3 2+2+3 1 157–161 56–63
A. formosanus 0.159 17 – = 1 29(27)-27-25 0 0 6 4–5 6–7 – 2+2 1 158–184 61–83
A. hainanus* 0.258 ~ 0.266 – – = 1 23-23-23 1 0 6 4–5 5 1–3 1+2+3(4) 1 165–168 67–69
A. huangjietangi 0.211 ~ 0.232 – 0.70 ~ 0.74 < 1 23-23-23 1 0 6 4–5 5–6 1–3(4) 2+2+3(4) 2 157–160 59–67
A. hunanensis 0.221 ~ 0.225 23 0.62 ~ 0.70 > 1 23-23-23 1 0 6 4–5 5–6 1–3(4) 2+2+4 2 163–165 69–72
A. jinggangensis 0.174 ~ 0.217 – – > 1 23-23-23 0 0 6 4–5 6 1–4 2(1)+2+3(4) 2 156–164 51–64
A. juliani 0.264 ~ 0.265 28 – > 1 25-23-23 1 0 6 4–5 6 1–3(4) 2+2+4 2 163–169 81–91
A. meiguensis 0.142 ~ 0.238 17 – – (21–23)-(19–21)-(19–21) 1 1 6 4–5 6 1–3 2(3)+2(3) 1 146–173 39–60
A. niger 0.151 ~ 0.179 – 0.67 < 1 25-25-23 1 0 6 4–5 6 1–3(4) 2+2(3) 2 169–185 52–72
A. ningshanensis* 0.121 ~ 0.161 – 0.45 ~ 0.58 = 1 23-23-23(21) 1 0 6 4–5 5 1–2(3) 2+2(3)+3(4) 1–2 159–174 41–46
A. panzhihuaensis 0.246 28 0.67 – 23-23-19 1 1 6 4–5 6 1–3 2+2+3 1 160 73
A. pingbianensis 0.243 – – = 1 23-23-23 0 0 7 5–6 6 1–3 2+2+3 1 164 56
A. rufescens 0.191 ~ 0.221 23 0.90 > 1 23-(23–25)-23 1 0 6 4–5 5 1–3 2(1)+2+3(4) 1–2 148–156 58–69
A. spinalis 0.150 ~ 0.250 16–20 – < 1 (23–25)-(23–25)-(23–25) 1 0 6 4–5 5–6 1–3 2+2(3) 1–2 138–175 48–67
A. timi 0.213 27 – > 1 25-25-23 0 0 6 4–5 6 1–3 2+2+3 1 170 72
A. tranganensis 0.254(+) 29 – > 1 25-23-23 1 0 6 4–5 6 1–3 2+2+3 2 171 73(+)
A. vanhoensis 0.264 32 – > 1 25-23-23 0 0 6/7 4–5/5–6 6 1–4 2+3+3 2 176 84
A. werneri 0.250 ~ 0.300 – – = 1 ?-(21–23)-? 1 0 6 4–5 6 – 2+3(4) – 157–191 67–98
A. yangdatongi 0.261 ~ 0.262 26 0.57 > 1 23-23-23 1 0 6 4–5 5–6 1–3 2+2+2/3 2 155-161 76-82
A. yunkaiensis 0.185 ~ 0.203 20–24 0.49 ~ 0.64 = 1 23-23-23 1 0 6 4–5 6 1–3(4) 2+2+3(4) 2 150–162 49–56
A. zugorum 0.229 28 – > 1 25-23-23 0 0 6 4–5 7 1–3 2+2+3 2 173 70
Table 5.
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Comparisons of main morphological characters of Achalinus nanshanensis sp. nov., A. yangdatongi, and Achalinus damingensis.

A. nanshanensis sp. nov. A. yangdatongi A. damingensis
Sex Males Males Females Males
SVL 300–392 241–293 292–424 322
TaL 99 85–104 73–93 105
TL 399–461 – – 427
TaL/TL 0.215–0.248 0.261–0.262 0.180–0.200 0.25
HL 10.07–10.95 8.5–11.60 9.52–11.45 –
HW 5.96–7.25 – – –
MT 18 26 24 –
ED 1.09–1.11 – – –
SPL 6/6 6/6 6/6(rarely 5/5) 6/6
SPL-Eye 4th–5th 4th–5th 4th–5th 4th–5th
IFL 6 5/6 6 6/6
Chin 2 2 2 2
IFL-1stChin 1st–3rd 1st–3rd 1st–3rd 1st–3rd
SPO 1 1 1 1
LorH / LorL 0.47–0.53 0.57 0.49 –
LSBI vs LSBP >1 >1 >1 >1
TEM 2+2(rarely 3)+4 2+2+2/3 2+2/3+2/3 2+2+3
aTEM-Eye 2 2 2 2
DSR 23(25)-23(25)-23(25) 23-23-23 23-23-23 23-23-23
VEN 147–158 155 170–171 165
SC 64–77 76 59–64 74
Anal 1 1 1 1

The new species differs from A. hunanensis Ma, Shi, Xiang, Shu & Jiang, 2023 in having fewer ventral scales (147–158 vs 163–165), maxillary teeth (18 vs 23), and a bright-yellow collar around the neck.

The new species differs from A. ningshanensis Yang, Huang, Jiang, Burbrink, Gong, Yu, Zhang, Huang & Huang, 2022 in having more infralabials (6 vs 5), two pairs of chin shields (vs 3 pairs), LSBI significantly longer than LSBP (vs suture between internasals is similar in length when compared to the suture between prefrontals).

The new species differs from A. ater in having more temporals (2+2/3+4 vs 2+2+3), fewer ventral scales (147–158 vs 160–170), more SC (64–77 vs 47–70) and a bright-yellow collar around the neck.

The new species differs from A. juliani Ziegler, Nguyen, Pham, Nguyen, Pham, van Schingen, Nguyen & Le, 2019 in having fewer ventral scales (147–158 vs 173–179), fewer subcaudals (64–77 vs 77–91), and a bright-yellow collar around the neck.

The new species differs from A. pingbianensis Li, Yu, Wu, Liao, Tang, Liu & Guo, 2020 in having a separated loreal (vs loreal fused with prefrontal), more subcaudals (64–77 vs 56), LSBI significantly longer than LSBP (vs length of suture between internasals subequal to that between prefrontals), two anterior temporals in contact with the eye (vs only the upper anterior temporal in contact with the eye), fewer supralabials (6 vs 7), and a bright-yellow collar around the neck.

The new species differs from A. timi Ziegler, Nguyen, Pham, Nguyen, Pham, Van Schingen, Nguyen & Le, 2019 in having one loreal (vs no loreals), more infralabials (6 vs 5), temporals (2+2/3+4 vs 2+2+3), fewer ventral scales (147–158 vs 170), and fewer tooth (18 vs 27).

The new species differs from A. vanhoensis Ha, Ziegler, Sy, Le, Nguyen & Luu, 2022 in having fewer ventral scales (147–158 vs 176), fewer subcaudals (64–77 vs 84) and more temporals (2+2/3+4 vs 2+3+3).

The new species differs from A. dabieshanensis Zhang, Liu, Huang & Zhang, 2023, A. huangjietangi Huang, Peng & Huang, 2021, A. niger Maki, 1931 and A. spinalis Peters, 1869 by LSBI significantly longer than LSBP (vs suture between internasals). Furthermore, the new species differs from A. dabieshanensis in having more infralabials (6 vs 5). It differs from A. huangjietangi and A. spinalis in having more subcaudals in males (64–77 vs 59–67 and 64–77 vs 48–67, respectively). It differs from A. niger in having comparatively longer tail (0.215–0.248 vs 0.151–0.179).

The new species differs from A. formosanus Boulenger, 1908, A. jinggangensis Zong & Ma, 1983 and A. zugorum Miller, Davis, Luong, Do, Pham, Ziegler, Lee, De Queiroz, Reynolds & Nguyen, 2020 in having a separated loreal (vs no loreal). Furthermore, the new species differs from A. formosanus in having fewer dorsal scale rows (23–25)-(23–25)-(23–25) vs (29)27-27-25). It differs from A. jinggangensis in having more subcaudals (64–77 vs 51–64) and from A. zugorum in having fewer infralabials (6 vs7) and more temporals (2+2/3+4 vs 2+2+3).

The new species differs from A. meiguensis Hu & Zhao, 1966 in having more dorsal scale rows (23-23-23 vs (21–23)-(19–21)-(19–21), more subcaudals (64–77 vs 50–60), and having two pairs of chin shields (vs three pairs of chin shields).

The new species differs from A. panzhihuaensis Hou, Wang, Guo, Chen, Yuan & Che, 2021 in having more temporals (2+2/3+4 vs 2+3+3) and fewer ventral scales (147–158 vs 160).

The new species differs from A. dehuaensis Li, Wu, Xu, Zhu, Ren, Guo & Dong, 2021 in having more infralabials (6 vs 5) and fewer maxillary teeth (18 vs 31–33), and a bright-yellow collar around the neck.

The new species differs from A. emilyae Ziegler, Nguyen, Pham, Nguyen, Pham, van Schingen, Nguyen & Le, 2019 in having more infralabials (6 vs 5), temporals (2+2/3+4 vs 2+2+3), and a bright-yellow collar around the neck, and the new species differs from A. emilyae in the color of its dorsum (brownish-black vs pale yellowish brown).

The new species differs from A. hainanus Huang, 1975 in having more infralabials (6 vs 5), temporals (2+2/3+4 vs 1+2+3(4) and LSBI significantly longer than LSBP (vs suture between internasals similar size when compared to the suture between prefrontals).

The new species differs from A. rufescens Boulenger, 1888 in having more infralabials (6 vs 5) and two pairs of chin shields (vs three pairs of chin shields).

The new species differs from A. tranganensis Luu, Ziegler, Ha, Lo, Hoang, Ngo, Le, Tran & Nguyen, 2020 in having more temporals (2+2/3+4 vs 2+2+3) and fewer ventral scales (147–158 vs 171).

The new species differs from A. werneri Van Denburgh, 1912 in having a shorter tail (0.215–0.248 vs 0.250–0.300), fewer ventrals (147–158 vs 157–191) and LSBI significantly longer than LSBP (vs suture between internasals similar size when compared to the suture between prefrontals).

The new species differs from A. yunkaiensis Wang, Li & Wang, 2019 in having a comparatively longer tail in males (0.215–0.248 vs 0.185–0.203), more subcaudals (64–77 vs 49–56) and LSBI significantly longer than LSBP (vs suture between internasals similar size when compared to the suture between prefrontals).

Discussion

With the discovery of Achalinus nanshanensis sp. nov., the number of Achalinus species now stands at 28, with 21 occurring in China: A. ater (Bourret, 1937), A. dabieshanensis (Zhang et al., 2023), A. damingensis (Yang et al., 2023), A. dehuaensis (Hou et al., 2021), A. emilyae (Ziegler et al., 2019), A. formosanus (Boulenger, 1908), A. hainanus (Huang, 1975), A. huangjietangi (Huang et al., 2021), A. hunanensis (Ma et al., 2023), A. jinggangensis (Zong & Ma, 1983), A. meiguensis (Hu & Zhao, 1966), A. niger (Maki, 1931), A. ningshanensis (Yang et al., 2022), A. panzhihuaensis (Hou et al., 2021), A. pingbianensis (Li et al., 2020), A. rufescens (Boulenger, 1888), A. sheni (Ma et al., 2023) A. spinalis (Peters, 1869), A. nanshanensis sp. nov. (this study), A. yangdatongi (Hou et al., 2021), and A. yunkaiensis (Wang et al., 2019). The genus Achalinus is known for its remarkable cryptic diversity, which has attracted extensive research. Nevertheless, some fundamental questions remain unanswered. Notably, a molecular comparison between populations of A. ater in Guangxi, China, and at its type locality at Tam Dao in northern Vietnam. Similarly, limited research has been made comparing A. spinalis found in China and at the type locality. This situation prompts us to reconsider the distribution of A. ater and A. spinalis in China.

Recent research has continued to underscore the remarkably high diversity within the genus Achalinus, which has lead to the discovery of an increasing number of species. However, several factors contribute to the difficulty in accurately identifying snakes of this genus based solely on morphology. Achalinus species display a conservative morphology; sexual dimorphism has been identified (particularly larger TaL/TL in males, more VEN in females, and more SC in males) (Ziegler et al. 2019; Hou et al. 2021; Huang et al. 2021; Li et al. 2021; Zhang et al. 2023); additionally, the possible existence of juvenile dimorphism has been suggested (Zhang et al. 2023). Furthermore, due to their secretive life history and morphological similarities, many cryptic species may well be hidden in plain sight within known widely distributed species (Ziegler et al. 2019; Li et al. 2020; Luu et al. 2020; Miller et al. 2020; Hou et al. 2021; Yang et al. 2022; Ma et al. 2023a; Yang et al. 2023). This poses a considerable challenge to future efforts aimed at comparing and identifying new species.

Molecular methods have played a pivotal role in the rapid discovery of Achalinus species (Yang et al. 2023). In addition, there are A. yunkaiensis and A. sheni distributed in the same region of A. nanshanensis sp. nov., which indicates that further study is necessary to conduct by using different geographic populations and molecular methods to revise their evolutionary history.

Acknowledgements

We thank Sheng-Chao Shi and Shun Ma (Chengdu Institute of Biology, Chinese Academy of Sciences) for their help in formal analysis.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

County biodiversity resources survey project in Miao Autonomous County of Chengbu, Hunan Province (no. 2021-326-430529); County Biodiversity Resources Survey Project in Dong Autonomous County of Tongdao, Hunan Province (no. 2021-326-430529); Central Financial Subsidy Project of Jintongshan National Nature Reserve in Hunan Province in 2022 (no. 2022-34).

Author contributions

Hui Li: methodology, formal analysis, validation, writing-original draft, writing-review and editing; Le-Qiang Zhu: methodology, investigation, formal analysis; Bei Xiao: methodology, formal analysis; Jie Huang: methodology, formal analysis; Shao-Wu Wu: methodology, investigation; Li-Xun Yang: methodology, investigation; Zhi-Qiang Zhang: conceptualization, data curation, project administration, resources, supervision, writing-review and editing; Xiao-Yang Mo: conceptualization, data curation, project administration, resources, supervision, writing-review and editing.

Author ORCIDs

Hui Li https://orcid.org/0009-0009-6318-3223

Le-Qiang Zhu https://orcid.org/0009-0006-3820-529X

Bei Xiao https://orcid.org/0009-0006-0740-5360

Jie Huang https://orcid.org/0009-0005-2565-3109

Shao-Wu Wu https://orcid.org/0009-0001-1769-2088

Li-Xun Yang https://orcid.org/0009-0008-3664-5333

Zhi-Qiang Zhang https://orcid.org/0009-0004-8658-9625

Xiao-Yang Mo https://orcid.org/0009-0003-2352-8975

Data availability

All of the data that support the findings of this study are available in the main text.

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