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Taxonomic and distributional revision of Pareas boulengeri (Reptilia, Squamata, Pareidae), including two new species from eastern and central China
expand article infoCai-wen Zhang‡, Shi-hang Xu‡, Tao Luo§, Chong Liu‡, Lei Yu‡, Jiang Zhou|, Tao Pan, Bao-wei Zhang‡
‡ Anhui University, Hefei, China
§ Yunnan University, Yunnan, China
| Guizhou Normal University, Guiyang, China
¶ Anhui Normal University, Wuhu, China

Corresponding author: Tao Pan ( pantao@ahnu.edu.cn )

Corresponding author: Bao-wei Zhang ( zhangbw@ahu.edu.cn )

Academic editor: Justin Bernstein
© 2025 Cai-wen Zhang, Shi-hang Xu, Tao Luo, Chong Liu, Lei Yu, Jiang Zhou, Tao Pan, Bao-wei Zhang.
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: Zhang C-wen, Xu S-hang, Luo T, Liu C, Yu L, Zhou J, Pan T, Zhang B-wei (2025) Taxonomic and distributional revision of Pareas boulengeri (Reptilia, Squamata, Pareidae), including two new species from eastern and central China. Zoosystematics and Evolution 101(4): 1621-1638. https://doi.org/10.3897/zse.101.156697
ZooBank: urn:lsid:zoobank.org:pub:468C419C-151E-4AE4-AC9E-25FE3992945E
Open Access

Abstract

The Boulenger’s slug snake (Pareas boulengeri Angel, 1920) has previously been documented as relatively widely distributed across the eastern, southern, and southwestern regions of China. In the present study, integrated morphological comparisons and molecular phylogenetic analyses were undertaken to reevaluate the taxonomic status of P. boulengeri and to describe two new species: Pareas dabieshanensis sp. nov. and Pareas orientalis sp. nov. Phylogenetic reconstruction based on CYTB gene sequences indicated that populations previously identified as P. boulengeri comprise three distinct lineages: true P. boulengeri, P. dabieshanensis sp. nov., and P. orientalis sp. nov. The two new species exhibit significant genetic divergence from their congeners, with uncorrected pairwise distances of 4.1–4.5%, consistent with interspecific divergence within the genus. Morphologically, P. dabieshanensis sp. nov. is distinguished by the presence of two subocular scales, the absence of preocular scales, and higher ventral (184–187) and subcaudal (68–74) counts. P. orientalis sp. nov. is characterized by a single preocular scale and fused subocular and postocular scales. The revised distributions restrict P. boulengeri to southwestern China, while the new species are confined to the Dabie Mountains (Anhui, Hubei, Henan) and eastern China (southern Anhui, Jiangsu, Jiangxi, Zhejiang), respectively. The non-overlapping ranges of P. dabieshanensis sp. nov. and P. orientalis sp. nov., bisected by the Yangtze River, suggest that this major hydrological system acted as a biogeographic barrier driving speciation. This study expands the genus Pareas to 33 recognized species (27 in China) and underscores the prevalence of cryptic diversity within morphologically conserved lineages.

Key Words

Cryptic species, geographic isolation, molecular phylogeny, morphology, speciation, Yangtze River

Introduction

Species of Pareas Wagler, 1830 (Squamata, Pareidae) are snail-eating or slug-eating, small, slender, arboreal nocturnal snakes. They possess a blunt snout, lack a mental groove, and have no teeth on the anterior maxilla (Hoso et al. 2007; Wallach et al. 2014; You et al. 2015; Poyarkov et al. 2022; Liu et al. 2023a). Their unique behavioral adaptation provides a considerable advantage within their ecological niche, allowing them to inhabit a vast region, including northeastern India, Myanmar, southern and eastern China, Indochina, and Sundaland. This broad distribution has ultimately led to the evolution of a diverse variety of species (You et al. 2015; Wang et al. 2020; Le et al. 2021; Liu and Rao 2021; Vogel et al. 2021; Poyarkov et al. 2022; Gong et al. 2023; Liu et al. 2023a, 2023b, 2024; Uetz et al. 2025). However, recent studies have suggested that the species diversity of Pareas has been severely underestimated, with 13 new species described and 8 resurrected since 2015 (Uetz et al. 2024). Thus, the genus Pareas now comprises 31 recognized species (Uetz et al. 2024), 22 of which are distributed in China (Liu et al. 2024; Uetz et al. 2025).

Among Pareas congeners, P. boulengeri (Angel, 1920) has a relatively wide distribution. This species was originally described based on a specimen from Guizhou Province in southwest China and named after George Albert Boulenger, a herpetologist at the British Museum of Natural History, London. Subsequently, P. boulengeri has been reported in multiple localities across eastern, southern, and southeastern China (Chen 1991; Zhao et al. 1998; Chen et al. 2006; Guo and Deng 2006; Zhao 2006). Notably, cryptic species have recently been identified within certain widespread Pareas species (Wang et al. 2020; Wu et al. 2023). Prior research has indicated genetic differentiation among P. boulengeri populations in Huangshan (Anhui) and the Dabie Mountains and in Henan Province (Wu et al. 2023). However, the phylogenetic relationships and taxonomic status of populations recorded as P. boulengeri in eastern and southwestern China remain undefined.

This study presents a detailed morphological examination and phylogenetic analysis of populations formerly identified as Pareas boulengeri. In addition, the species boundaries and distribution of P. boulengeri are redefined, and two new species from the Dabie Mountains and eastern China are described.

Materials and methods

Sampling

This study was approved by the Institutional Animal Care and Use Committee of the School of Life Sciences at Anhui University (project number IACUC(AHU)-2022-050). We collected twenty-one specimens (13 adult females and 8 adult males) previously classified as Pareas boulengeri: 12 (females: 3, males: 9) from Anhui and Zhejiang provinces and 9 (females: 5, males: 4) from Guizhou Province, China (Fig. 1). After photographing the individuals, they were euthanized using isoflurane, fixed in 10% formaldehyde for two days, and subsequently washed and preserved in 75% ethanol. Liver tissue samples were collected from all specimens and preserved in 95% ethanol before fixation. The new vouchered specimens were deposited at the Anhui University Biology Museum (AHUBM).

Figure 1. 

Data locations pertinent to this research. The black dots indicate current distribution points of Pareas boulengeri, as documented in GBIF. The red, blue, and yellow circles denote the sampling sites for P. boulengeri, P. dabieshanensis, and P. orientalis, respectively. This map includes both actual sampling sites and approximate locations associated with sequence data obtained from NCBI. The dotted circles in red, blue, and yellow represent the potential distribution ranges of the three species under investigation.

In addition, 18 P. boulengeri samples from various sources (Table 1), along with their respective sampling localities, were obtained from the National Center for Biotechnology Information (NCBI). Distribution records for P. boulengeri were also downloaded from the Global Biodiversity Information Facility (GBIF) to update the species’ distribution range (Fig. 1).

Table 1.
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Samples used in the molecular analyses, including GenBank numbers, voucher IDs, and localities.

ID Species Locality Voucher ID GenBank no. Source
1 P. abros Song Thanh, Quang Nam, Vietnam ZMMU R-16393 MZ712235 Poyarkov et al. 2022
2 P. andersonii Mt. Natmataung, Chin, Myanmar CAS 235359 MT968772 Vogel et al. 2020
3 P. atayal N. Cross Is. Hw., Taiwan, China NMNS 05594 KJ642122 You et al. 2015
4 P. baiseensis Baise, Guangxi, China ANU000220008 OQ054329 Gong et al. 2023
5 P. berdmorei Kin Pon Chaung, Mon, Myanmar CAS 240362 MZ712219 Poyarkov et al. 2022
6 P. boulengeri Jiangkou, Guizhou, China GP 2923 MK135090 Wang et al. 2020
7 P. boulengeri Anxian, Sichuan, China GP 207 MK135091 Wang et al. 2020
8 P. boulengeri Wufeng, Hubei, China YBU 13323A MK135092 Wang et al. 2020
9 P. boulengeri Yidu, Hubei, China GP 4716 MK135093 Wang et al. 2020
10 P. boulengeri Fenghua, Zhejiang, China SYSr001769 MK201584 Li et al. 2020
11 P. boulengeri Yixian, Anhui, China GP 3428 MK135094 Wang et al. 2020
12 P. boulengeri Chunan, Zhejiang, China YBU 17155 MK135095 Wang et al. 2020
13 P. boulengeri Chunan, Zhejiang, China YBU 17245 MK135096 Wang et al. 2020
14 P. boulengeri Mianyang, Sichuan, China HS09001 MK201240 Li et al. 2020
15 P. boulengeri Huangshan, Anhui, China HS14024 MK201241 Li et al. 2020
16 P. boulengeri Enshi, Hubei, China KIZ 09965 JF827678 Guo et al. 2011
17 P. boulengeri jiannan, Hubei, China KIZ 09966 JF827679 Guo et al. 2011
18 P. boulengeri jianzhuxi, Hubei, China KIZ 09967 JF827680 Guo et al. 2011
19 P. boulengeri Luxi,Hunan, China KIZ 09968 JF827681 Guo et al. 2011
20 P. boulengeri Shennongjia, Hubei, China KIZ 09969 JF827682 Guo et al. 2011
21 P. boulengeri Luxi,Hunan, China KIZ 09970 JF827683 Guo et al. 2011
22 P. boulengeri Shennongjia, Hubei, China KIZ 09971 JF827684 Guo et al. 2011
23 P. boulengeri Qimen, Anhui, China HSR18074 MN866896 Huang et al. 2020
24 P. boulengeri Huangping, Guizhou, China GZNU2018051502 PV804873 This study
25 P. boulengeri Huangping, Guizhou, China GZNU2018051503 PV804874 This study
26 P. boulengeri Huangping, Guizhou, China GZNU20180515017 PV804875 This study
27 P. boulengeri Liupangshui, Guizhou, China LPSSY2024070903 PV804876 This study
28 P. boulengeri Liupangshui, Guizhou, China LPSSY2022070601 PV804877 This study
29 P. dabieshanensis sp. nov. Jinzhai, Anhui,China AHU2024042601 PV804864 This study
30 P. dabieshanensis sp. nov. Yuexi, Anhui,China AHU2014100801 PV804866 This study
31 P. dabieshanensis sp. nov. Huoshan, Anhui, China AHU2021050201 PV804865 This study
32 P. dabieshanensis sp. nov. Huoshan, Anhui, China AHU2024042601 PV804867 This study
33 P. orientalis sp. nov. Chunan, Zhejiang, China AHU2021101501 PV804869 This study
34 P. orientalis sp. nov. Jing, Anhui, China AHU2019061201 PV804868 This study
35 P. orientalis sp. nov. Xiuning, Anhui, China AHU2024110501 PV804870 This study
36 P. orientalis sp. nov. Huangshan, Anhui, China AHU2024072201 PV804871 This study
37 P. orientalis sp. nov. Xiuning, Anhui, China AHU2024051502 PV804872 This study
38 P. carinatus Sungai Sedim, Kedah, Malaysia LSUHC10604 KC916748 Loredo et al. 2013
39 P. chinensis Hongya, Sichuan, China GP 2383 MK135089 Wang et al. 2020
40 P. dulongjiangensis Gongshan, Yunnan, China KIZ R201607 OQ718498 Liu et al. 2023b
41 P. formosensis N. Cross Is. Hw., Taiwan, China NMNS 05632 KJ642130 You et al. 2015
42 P. geminatus Jiangcheng, Yunnan, China CIB 118021 MW287068 Ding et al. 2020
43 P. guanyinshanensis Yuanyang, Yunnan, China KIZ 2023038 PP215390 Liu et al. 2023a
44 P. hamptoni Kachin, Myanmar, YPX 18219 MK135077 Wang et al. 2020
45 P. iwasakii Ishigaki Is., S. Ryukyu, Japan I03-ISG1 KJ642158 You et al. 2015
46 P. kaduri Lohit, Arunachal, India BNHS 3574 MT188734 Bhosale et al. 2020
47 P. komaii Lijia, Taitung, Taiwan, China HC 000669 JF827687 Guo et al. 2011
48 P. kuznetsovorum Song Hinh, Phu Yen, Vietnam ZMMU R-16802 MZ712232 Poyarkov et al. 2022
49 P. macularius Bago, Myanmar CAS 206620 AF471082 Guo et al. 2011
50 P. margaritophorus Cangwu, Guangxi, China YBU 16061 MK135097 Wang et al. 2020
51 P. modestus Tanhril, Aizawl, Mizoram, India MZMU 1293 MT968773 Vogel et al. 2020
52 P. monticola Medog, Tibet, China GP 2027 MK135107 Wang et al. 2020
53 P. niger Kunming, Yunnan, China KIZ 059339 MW436706 Liu and Rao 2021
54 P. nigriceps Mt. Gaoligong, Yunnan, China SYSr001222 MK201455 Li et al. 2020
55 P. nuchalis Belait, Brunei FK 2626 MZ603794 Le et al. 2021
56 P. stanleyi Guilin, Guangxi, China HM 2007-S001 JN230704 Guo et al. 2011
57 P. temporalis Da Huoai, Lam Dong, Vietnam UNS 09992 MZ603793 Le et al. 2021
58 P. tigerinus Menghai, Yunnan, China KIZ 20210703 OP752143 Liu et al. 2023b
59 P. victorianus Mt. Natmataung, Chin, Myanmar CAS 235254 MW438300 Vogel et al. 2021
60 P. vindumi Lukpwir, Kachin, Myanmar CAS 248147 MT968776 Vogel et al. 2020
61 P. xuelinensis Lancang, Yunnan, China KIZ XL1 MW436709 Liu and Rao 2021
62 P. yunnanensis Dali, Yunnan, China, KIZ 2022033 OP752146 Liu et al. 2023a
63 Aplopeltura boa Malaysia LSUHC 7248 KC916746 Loredo et al. 2013

Molecular data and phylogenetic analyses

Purified DNA was extracted from liver tissue using a standard phenol/chloroform extraction method (Sambrook et al. 1989). Partial sequences of the mitochondrial cytochrome b gene (CYTB) were amplified and sequenced using the following primers: L14910 (5′-GACCTGTGATMTGAAAACCAYCGTTGT-3′) and H16064 (5′-CTTTGGTTTACAAGAACAATGCTTTA-3′) (Lawson et al. 2005). Polymerase chain reaction (PCR) was conducted in a 25-μL volume. Each reaction contained 100 ng of template DNA, 0.3 mM of each primer, and 10 μL of Premix Ex Taq™ (Takara). The PCR protocol included an initial denaturation at 94 °C for 3 min; followed by 35 cycles of denaturation at 94 °C for 30 s, annealing at 52 °C for 40 s, and extension at 72 °C for 90 s; and a final extension at 72 °C for 10 min. PCR products were purified using an EasyPure PCR Purification Kit, following the manufacturer’s instructions (TransGene). Each fragment was sequenced bidirectionally using an ABI 3730 semi-automated sequencer (PE Applied Biosystems). Amplified products were submitted to General Biology (Anhui) Co., Ltd. (Chuzhou, China), and resulting sequences were deposited in GenBank (accession numbers provided in Table 1).

According to the species list on the Reptile Database (Uetz et al. 2025), gene sequences of all recognized Pareas species were downloaded from GenBank to enable comprehensive phylogenetic comparisons. Additionally, sequences for Aplopeltura boa were obtained from GenBank and used as the outgroup. A total of 105 sequences from 47 individuals representing 16 species were included (Table 1).

CYTB sequence alignment was performed using MAFFT 7.110 with the G-INS-i algorithm (Katoh et al. 2005; Katoh and Standley 2013). The resulting alignments were trimmed with BioEdit 7.0.5.3 to remove low-quality bases at both ends (Hall 1999), and the final dataset was manually merged. jModelTest was used to select the best-fitting evolutionary model based on the corrected Akaike Information Criterion (AIC) (Guindon and Gascuel 2003; Posada 2008; Akaike 1974). The best-fitting model was selected by comparing the log-likelihood, AIC, and BIC values across multiple models, choosing the one with the lowest AIC or BIC (Akaike 1974). Bayesian inference (BI) was performed using MrBayes 3.2.4 (Ronquist et al. 2012), and maximum likelihood (ML) analysis was conducted using RAxMLGUI 1.3 (Silvestro and Michalak 2012). For BI, two parallel runs of 10,000,000 generations were executed, with trees sampled every 1,000 generations. The first 25% of samples were discarded as burn-in, and the remaining trees were used to generate a 50% majority-rule consensus tree. Bayesian posterior probabilities (BPPs) were calculated. The potential scale reduction factor (PSRF) was < 0.005, and the error rate was < 0.01. Markov Chain Monte Carlo (MCMC) convergence was assessed using Tracer v1.5 (Rambaut et al. 2024), confirming that all effective sample sizes (ESSs) exceeded 200 and PSRFs were close to 1.0.

Morphological analyses

In accordance with previous studies (Dowling 1951; Zhao 2006; Vogel 2015), 22 commonly used morphological characteristics were assessed in adult slug-eating snake samples, comprising 6 mensural and 16 meristic traits, using established terminologies and methods. Body morphological measurements were typically recorded to the nearest 1 mm using a measuring tape, while others were recorded to the nearest 0.1 mm using an electronic slide caliper. The morphological measurements included snout–vent length (SVL), the distance from the tip of the snout to the posterior edge of the vent ; tail length (TaL) ; total length (TL), the distance from the snout tip to the tail end ; relative tail length (TaL/TL) ; head length (HL), the distance from the snout tip to the jaw angles ; maximal head width (HW), the distance across the widest part of the head and eye diameter (ED), the distance from the anterior corner to the posterior corner of the eye.

The meristic characteristics evaluated included the number of dorsal scale rows counted at one head length behind the head (ASR) , midbody (MSR , specifically at SVL/2) , and one head length before the vent (PSR) ; enlarged vertebral scale rows (VSE) ; keeled dorsal scale rows at midbody (KMD) ; ventral scales (VEN) ; subcaudal scales (SC) ; cloacal plates (CP) ; supralabials (SPL) ; infralabials (IFL) ; anterior temporals (At) ; posterior temporals (Pt) ; loreals (LOR) ; preoculars (Preoc) ; suboculars (SoO) and postoculars (PoO). The values for paired head characteristics were recorded on both sides of the head in a left/right order.

Comparative data for various species were obtained from pertinent publications, including those by Boulenger (1900, 1905, 1914), Ota et al. (1997), Zhao et al. (1998), Malkmus et al. (2002), Guo and Zhao (2004), Jiang (2004), Zhao (2006), Guo and Deng (2006), Stuebing et al. (2014), Vogel (2015), You et al. (2015), Bhosale et al. (2020), Ding et al. (2020), Suntrarachun et al. (2020), Vogel et al. (2020), Wang et al. (2020), Le et al. (2021), Liu and Rao (2021), Vogel et al. (2021), Poyarkov et al. (2022), Gong et al. (2023), Liu et al. (2023a, 2023b), Oskyrko et al. (2024), and Liu et al. (2024).

Teeth counts and dentition asymmetry

X-ray scanning was conducted using nano-computed tomography. Specimens were examined with a GE v|tome|x m dual-tube 300/180 kV system at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Chinese Academy of Sciences. Each specimen was scanned with an energy beam of 80 kV and a flux of 80 μA, employing a 360° rotation. The data were subsequently reconstructed into a 4096 × 4096 matrix comprising 1,536 slices. The final computed tomography (CT)–reconstructed skull images were exported, achieving a spatial resolution of approximately 6.1 μm. The skull images were derived from virtual three-dimensional models reconstructed using Volume Graphics Studio 3.0. The quantities of maxillary teeth (MX), palatine teeth (PAL), pterygoid teeth (PT), and dentary teeth (DT) were enumerated.

Results

Phylogenetic analyses

The aligned dataset comprised genes from 62 individuals of the Pareas genus and one from the outgroup Aplopeltura boa (Table 1). The dataset for the CYTB regions included 63 collections representing 34 taxa, resulting in a concatenated alignment of 1,096 characters. GTR + I + G was identified as the best-fit evolutionary model. The maximum likelihood (ML) search was terminated after 200 bootstrap (BS) replicates. For the Bayesian inference (BI), all chains converged after 2 million generations, with an average standard deviation of split frequencies of 0.006923 and an average ESS of 1,450. The ML and BI algorithms produced similar topologies for the main lineages; therefore, only the topology generated by the ML algorithm is presented, with BS values and BPPs > 50% and 0.90, respectively, shown at the nodes (Fig. 2).

Figure 2. 

Maximum likelihood and Bayesian inference phylogenies based on mitochondrial CYTB genes. ML bootstrap support (BS)/Bayesian posterior probabilities (PP) are shown at nodes. Values are not displayed if BS < 50 or PP < 0.90. “white star” indicates holotype gene sequences.

Three independent lineages were identified within the 32 specimens previously classified as Pareas boulengeri. The samples from western China, the Dabie Mountains, and eastern China formed distinct lineages, each exhibiting strong support and low intra-lineage divergence. The two unnamed lineages (Dabie Mountains group and eastern China group) were identified as sister taxa and were closely related to P. boulengeri (western China group).

Genetic distances based on the CYTB gene among Pareas species are presented in Suppl. material 1: table S1. The two putative new species from the Dabie Mountains and eastern China exhibited significant genetic divergence from other congeners. Compared to closely related recognized congeners, the minimum uncorrected genetic distance was 4.1% between the clades from the Dabie Mountains and eastern China. Additionally, the minimum uncorrected genetic distances between the unnamed species and P. boulengeri from western China were 4.3% (between P. boulengeri and the Dabie Mountains group) and 4.5% (between P. boulengeri and the eastern China group). These distances were comparable to the interspecific distances among other recognized congeners, such as 4.3% between P. hamptoni and P. guanyinshanensis and 4.1% between P. yunnanensis and P. geminatus (Suppl. material 1: table S1).

Taxonomic account

Combining molecular phylogenetic analysis and morphological comparisons indicated that specimens from the Dabie Mountains and eastern China (southern Anhui, Jiangxi, and Zhejiang), previously classified as Pareas boulengeri, are distinct from the type locality and significantly differ from other known species within the genus Pareas. Accordingly, comprehensive taxonomic accounts and updated diagnoses for P. boulengeri were prepared, and the two new species were characterized.

Pareas Boulengeri (Angel, 1920)

Amblycephalus Boulengeri (Angel, 1920).

Amblycephalus monticola boulengeri (Mell, 1931).

Pareas boulengeri (Hu et al. 1973; Zhao et al. 1998, Chen et al. 2006; Guo and Deng 2006; Zhao 2006; Wallach et al. 2014; Vogel 2015).

Pareas (Eberhardtia) boulengeri (Poyarkov et al. 2022).

Type locality.

Région de Koeï Tchéou, Chine.” [=Guizhou region, southeastern China, ca. 27°N, 107°E].

Syntypes.

MNHN-RA 1912.0349 (470 mm specimen), MNHN-RA 1912.0350 (82 mm specimen), and MNHN-RA 1912.0351 (460 mm specimen) (Révérend Père avalerie).

Specimens examined.

Nine specimens were assessed (3 females and 6 males); all were molecularly identified as the species Pareas boulengeri. Four of the specimens were obtained from Liupanshui Normal University in Shuicheng City, Guizhou Province, China, with the following identifiers: LPSSY2024070903 (male), LPASY2022070601 (male), LPSSY2021070801 (female), and LPSSY2024070902 (female). One specimen was collected from the Shuicheng District of Liupanshui City: LPSSC2024070502 (female). One specimen was obtained from Yushe National Forest Park in Shuicheng City, Liupanshui City: LPSYS2022062802 (female). The remaining three specimens were obtained from Huangping County, Qiandongnan Miao and Dong Autonomous Prefecture, Guizhou Province: GZNU20180515017 (female), GZNU2018052303 (male), and GZNU2018052302 (male).

Common name.

The common English name is Boulenger’s Slug Snake; the common Chinese name is 平鳞钝头蛇 (Píng Lín Dùn Tóu Shé).

Etymology.

Revised diagnosis: Pareas boulengeri can be distinguished from its congeners by a combination of the following characteristics (Fig. 3): (1) medium body size (TL 308–566 mm, n = 5 females; 362–565 mm, n = 6 males); (2) gray–brown or tan body, with many dorsal scales and covered with dark brown spots; (3) length of suture between internasals is distinctly shorter than that between the prefrontals, with a prefrontal bordering orbit; (4) frontal is subhexagonal to diamond-shaped, with its lateral sides converging posteriorly; (5) anterior pair of chin shields is longer than broad, with the loreal bordering the orbit; (6) the prefrontal contacts the eye, and there is one subocular scale with no preocular scales; (7) 7–8 supralabials and 9 infralabial scales; (8) rows of 15-15-15 dorsal scales, mid-dorsal scales smooth, and the vertebral scale row is not enlarged; (9) 175–188 ventrals scales, 57–66 subcaudals scales, divided, with a single cloacal plate; (10) prefrontal and postfrontal bones exhibit contact, asymmetric teeth number in maxilla, palatine, pterygoid, and dentary bones (MX 4–5/5, PAL 3/3, PT9–13/9–11, DT 16–18/20–21); (11) dorsal surface of the head displays a dense configuration of black, coarse spots; two black longitudinal stripes extend posteriorly, located behind the parietal and supraocular scales, converging into a prominent black stripe in the neck region; a slender black horizontal line is present on the lateral aspect of the head, posterior to the eye and extending toward the corner of the mouth.

Figure 3. 

Pareas boulengeri in preservative (LPSSC2024070502). A. Dorsal view; B. Ventral view; C. Right lateral view of the head; D. Left lateral view of the head; E. Ventral view of the head; F. Dorsal view of the head. Scale bars: 10 mm.

Remarks.

The type locality of Pareas boulengeri is in the “Région de Koeï Tchéou, Chine” [=Guizhou region, southeastern China, approximately 27°N, 107°E], according to the original description; however, the specific locus remains unknown. Subsequently, this species has been reported from multiple localities in central, eastern, and southern China (Zhao et al. 1998; Chen et al. 2006; Guo and Deng 2006). However, based on voucher specimens and molecular data from this study, P. boulengeri is currently only within Chongqing, Hunan, Guizhou, Hubei, and Sichuan. The populations in southern Gansu and southern Shaanxi are temporarily classified as P. boulengeri. Previous records from the Dabie Mountains, at the junction of Anhui, Henan, and Hubei, should be assigned to P. dabieshanensis sp. nov. (Chen et al. 2006; Pan et al. 2014; this study), while previous records from southern Anhui, Jiangxi, and Zhejiang should be assigned to P. orientalis sp. nov. (this study).

Pareas dabieshanensis Zhang, Pan & Zhang, sp. nov.

https://zoobank.org/C4F4089A-7A85-44E7-B8D9-C4747DA54D72

Pareas boulengeri (Chen et al. 2006; Pan et al. 2014). Chresonymy.

Type materials.

Holotype : • An adult male (Fig. 4, AHU2024042601) was collected from the Tianma National Nature Reserve (31.2250°N, 115.6831°E; elevation 807 m a.s.l.) in Jinzhai County, Luan City, Anhui Province, China, by Tao Pan and Wen-gang Li on April 26, 2024.

Figure 4. 

Pareas dabieshanensis sp. nov. in preservative (AHU2024042601). A. Dorsal view; B. Ventral view; C. Right lateral view of the head; D. Left lateral view of the head; E. Ventral view of the head; F. Dorsal view of the head. Scale bars: 10 mm.

Paratypes : • One adult male specimen (AHU2014100801) was collected from the Yaoluoping National Nature Reserve in Yuexi County, Anqing City, Anhui Province, China, by Tao Pan on October 08, 2014. • One adult male specimen (AHU2021050201) was collected from the Taiyang Township in Huoshan County, Luan City, Anhui Province, China, by Caiwen Zhang on May 02, 2021.

Etymology.

Pareas dabieshanensis sp. nov. refers to the distribution of the new species in the Dabie Mountains. We recommend designating this new species Dabie Mountains Slug-eating Snake and 大别山钝头蛇 (Dà Bié Shān Dùn Tóu Shé).

Diagnosis.

Pareas dabieshanensis sp. nov. is distinguished from its congeners by several morphological characteristics (Table 2): (1) medium body size (TL 443–517 mm, n = 3 males); (2) yellow–brown body featuring numerous irregular black horizontal stripes; (3) the length of the suture between the internasals is subequal to that between the prefrontals, with the prefrontal bordering the orbit; (4) the frontal is subhexagonal to diamond-shaped, with its lateral sides converging posteriorly; (5) the anterior pair of chin shields is longer than broad; the loreal scale partially borders the orbit; (6) the prefrontal contacts the eye, and there are two subocular scales; (7) 7–8 supralabials and 9 infralabial scales; (8) 15-15-15 rows of dorsal scales, with mid-dorsal scales smooth, and the vertebral scale row is not enlarged; (9) 184–187 ventral scales and 68–74 subcaudals, divided, with a single cloacal plate; (10) prefrontal and postfrontal bones do not exhibit contact, asymmetric teeth number in maxilla, palatine, pterygoid, and dentary bones (MX 5/5, PAL 3/3, PT10–11/9–11, DT 16–18/20); (11) dorsal surface of the head exhibits a dense arrangement of small, black spots; three distinct black vertical stripes on the lateral aspect of the head, which do not converge; the central horizontal stripe, posterior to the supraorbital scales, extends posteriorly toward the neck; additionally, a horizontal stripe posterior to the eyes terminates at the posterior margin of the head; two black horizontal stripes are in the supraocular and postocular regions, extending only to the posterior margin of the head.

Table 2.
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Comparisons of morphometric and scalation data for Pareas boulengeri, P. dabieshanensis sp. nov., and P. orientalis sp. nov. Measurements in mm. For a list of abbreviations, please refer to the Materials and Methods section.

Characters Pareas boulengeri (n = 9) P. dabieshanensis sp. nov. (n = 3) P. orientalis sp. nov. (n = 9)
SVL 250–464 346–413 247–412
TaL 58–107 97–108 64–112
TL 308–566 443–517 311–524
TaL/TL 0.18–0.23 0.20–0.22 0.19–0.21
HL 12.30–20.79 15.9–19.48 12.72–19.24
HW 5.22–10.37 6.14–9.01 5.48–9.11
ED 2.41–3.27 2.53–2.87 2.27–3.1
ASR 15 15 15
MSR 15 15 15
PSR 15 15 15
VSE 0 0 0
KMD 0 1 0
VEN 175–188 184–187 175–187
SC 57–66 68–74 69–75
CP entire entire entire
SL 7–8 7–8 7–8
IL 9 9 9
At 2 2 2
Pt 3 3 3
Preoc 0 0 1
SoO Fused 2 Fused
PoO Fused Fused Fused
LOR 1 1 1

Holotype description.

An adult male with a total length of 506 mm (SVL 398 mm, TaL 108 mm); relatively short tail (TaL/TL ratio 0.21); body slender, slightly compressed; head distinct from neck, snout wide and blunt, projecting beyond lower jaw; head elongate, clearly distinct from neck; snout round in dorsal view; eye slightly enlarged, pupil vertical and slightly elliptical; rostral approximately as wide as high, slightly visible from above; nasal undivided; internasal elongated; prefrontal, approximately trapezoidal, bordering orbits; frontal shield-shaped, slightly longer than wide; parietals large, longer than wide, gradual narrowing posteriorly, median suture approximately equal to length of frontal; one loreal, in contact with eye; two subocular scales, the anterior scale is diminutive, and the posterior scale is fused with the postocular scale, extending anteriorly beneath the eyes; temporals 2+3/2+3; 7/8 supralabial scales; 9/9 infralabials; 3 chin-shield pairs; dorsal scales exhibit a smooth texture and are arranged in 15 rows along the body, while the dorsal scale does not exhibit enlargement; 190 ventral scales; 70 subcaudals scales, paired; single cloacal plate. Prefrontal and postfrontal bones do not exhibit contact, asymmetric teeth number in maxilla, palatine, pterygoid, and dentary bones (MX 5/5, PAL 3/3, PT10/9, DT 18/21).

Coloration in life.

Dorsal surface of the head exhibits a dense arrangement of small, black spots; three distinct black vertical stripes appear on the lateral aspect of the head and do not converge; the central horizontal stripe, posterior to the supraorbital scales, extends posteriorly toward the neck. A horizontal stripe posterior to the eyes terminates at the posterior margin of the head. Furthermore, two black horizontal stripes in the supraocular and postocular regions extend only to the posterior margin of the head. The dorsal surface is further distinguished by a yellowish-brown coloration featuring 47 irregular and discontinuous black horizontal stripes. In contrast, the ventral side exhibits a grayish-white coloration, adorned with scattered fine black spots.

Coloration in preservative.

In its preserved form (Fig. 4), the specimen’s coloration resembles its living appearance. However, the once yellowish–red dorsal surfaces of the head and body fade to a pinkish–brown, with a notable reduction in vibrancy. The black stripes along the sides of the body and tail remain visible, preserving their contrast despite the fading in other areas. The pinkish–yellow belly and ventral portion of the head and tail also lighten to a pinkish–white. Moreover, the iris becomes grayish-black, while the pupil becomes white, reflecting additional changes in pigmentation due to the preservation process.

Variation.

The three adult male specimens exhibited nearly identical morphological characteristics. The fundamental statistics related to the morphological measurements are presented in Suppl. material 1: tables S2, S3. The number of posterior temporals ranged from two to three. The number of vertical black stripes on each side of the body ranged from 48 to 53, while the iris color in the paratypes varied from reddish-yellow to yellow.

Distribution and habitat.

Based on the existing distribution data, it is speculated that this species is mainly distributed in the Dabie Mountain area at the junction of Anhui, Henan, and Hubei Province (Fig. 1). It inhabits mountainous regions, frequently residing near low shrubs adjacent to streams in low-altitude areas, and primarily feeds on slugs and snails.

Comparison.

Comparisons between the new species and its congeners are summarized in Table 2. Pareas dabieshanensis sp. nov. was previously classified as P. boulengeri. However, this newly identified species can be differentiated from P. boulengeri in southwest China based on a higher number of subcaudal scales (68–74 vs. 57–66), two subocular scales (vs. one and fused suboculars with postoculars) (Fig. 5), and prefrontal and postfrontal bones do not exhibit contact (vs. contact) (Fig. 6).

Figure 5. 

Comparative analysis of head scaling. Specimens include. A. Pareas boulengeri (LPSSC2024070502); B. A living specimen (GZNU2018052302); C. The holotype of P. dabieshanensis sp. nov. (AHU2024051501); D. A living specimen (AHU2021050201); E. The holotype of P. orientalis sp. nov. (AHU2024051501); and F. A living specimen (AHU2024051502). Photos by Cai-wen Zhang, Shan Shen, and Tao Luo.

Figure 6. 

Three-dimensional model of the skull of Pareas boulengeri, P. dabieshanensis sp. nov., and P. orientalis sp. nov. Left, right lateral view; middle, left lateral view; right, dorsal view. A–C. Pareas boulengeri (LPSSY2021070801); D–F. The holotype of P. dabieshanensis sp. nov. (AHU2024051501); H–J. The holotype of P. orientalis sp. nov. (AHU2024051501). Implemented by Cai-wen Zhang and Jing-song Shi. Scale bars: 2 mm.

Pareas dabieshanensis sp. nov. can be distinguished from P. andersonii, P. macularius, P. margaritophorus, and P. modestus by its yellow–brown dorsum featuring irregular dark bands (vs. uniform grey to black to dark coloration with bicolored spots), the loreal contacting the eye (vs. the loreal not contacting the eye), a greater number of ventral scales (184–187 vs. 141–162, 151–173, 133–160, or 151–159, respectively), and a greater number of subcaudals (68–74 vs. 35–47, 57–66, 35–54, or 35–46, respectively).

Pareas dabieshanensis sp. nov. can be easily distinguished from P. abros, P. atayal, P. baiseensis, P. berdmorei, P. carinatus, P. formosensis, P. geminatus, P. guanyinshanensis, P. hamptoni, P. kaduri, P. komaii, P. kuznetsovorum, P. niger, P. nuchalis, P. temporalis, P. tigerinus, and P. xuelinensis by the presence of a loreal scale in contact with the eye (vs. the loreal scale not contacting the eye).

Pareas dabieshanensis sp. nov. can be distinguished from P. chinensis by the absence of preoculars (vs. one preocular), two subocular scales, one of which is fused with the postocular scale (vs. not fused), dorsal scales not enlarged (vs. one vertebral scale row enlarged), and dorsal scale smooth at midbody (vs. three keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from Pareas dulongjiangensis by lacking preoculars (vs. one preocular), having two subocular scales, one of which is fused with the postocular scale (vs. only one and suboculars fused with postoculars), dorsal scales not enlarged (vs. three vertebral scale rows enlarged), and a dorsal scale smooth at midbody (vs. five keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. can be easily distinguished from Pareas iwasakii by the absence of preoculars (vs. one preocular), having postoculars fused with suboculars (vs. distinct and separated postoculars and suboculars), fewer ventral scales (184–187 vs. 190–193), fewer subcaudal scales (68–74 vs. 76–84), dorsal scales not enlarged (vs. one vertebral scale row enlarged), and dorsal scale smooth at midbody (vs. 5–7 keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from P. monticola with more infralabial scales (9 vs. 7–8) and a smooth dorsal scale at midbody (vs. 1–3 keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from P. nigriceps by having more infralabial scales (9 vs. 7), lacking preoculars (vs. one preocular), having two anterior temporals (vs. one anterior temporal), two subocular scales, one of which is fused with the postocular scale (vs. only one and suboculars fused with postoculars), dorsal scales that are not enlarged (vs. one enlarged vertebral scale row), and a smooth dorsal scale at midbody (vs. 9 keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from P. stanleyi by having more infralabial scales (9 vs. 7–8), postoculars fused with suboculars (vs. distinct and separated postocular and subocular), more ventral scales (184–187 vs. 151–160), more subcaudal scales (68–74 vs. 48–64), and a smooth dorsal scale at midbody (13 keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from P. victorianus by having more infralabial scales (9 vs. 6–7), two subocular scales, one of which is fused with the postocular scale (vs. only one and subocular fused with postocular), more ventral scales (184–187 vs. 164), more subcaudal scales (68–74 vs. 58), dorsal scales not enlarged (vs. one enlarged vertebral scale row), and a smooth dorsal scale at midbody (vs. eight keeled dorsal scale rows at midbody).

Pareas dabieshanensis sp. nov. differs from P. vindumi by having more supralabials (7–8 vs. 6), more infralabials (9 vs. 6), two subocular scales, one of which is fused with the postocular scale (vs. only one and subocular fused with postocular), more ventral scales (184–187 vs. 178), and more subcaudal scales (68–74 vs. 61).

Pareas dabieshanensis sp. nov. differs from P. yunnanensis by having more infralabials (9 vs. 6), lacking preoculars (vs. 1–2 preoculars), having two subocular scales, one of which is fused with the postocular scale (vs. only one and subocular fused with postocular), more ventral scales (184–187 vs. 169–175), more subcaudal scales (68–74 vs. 59–65), dorsal scales not enlarged (vs. one enlarged vertebral scale row), and a smooth dorsal scale at the midbody (vs. 5–7 keeled dorsal scale rows at midbody).

Remarks.

In 1974, the Sichuan Institute of Biology first discovered Pareas chinensis in the Dabie Mountains of Anhui Province. The amphibian and reptile fauna of Anhui suggest that this species is also present in Qianshan and Huoshan County (Chen 1991). Additionally, Chen et al. (2006) identified P. boulengeri for the first time in the Jingangtai National Nature Reserve, in the Dabie Mountains of Henan Province. Pan et al. (2014) further confirmed the presence of this species in the Dabie Mountains of Anhui and reclassified P. chinensis as P. boulengeri. This species has been detected in multiple localities within the Dabie Mountains (Pan et al. 2014; this study). Furthermore, P. dabieshanensis sp. nov. is likely found in eastern Hubei, which is geographically connected to western Anhui; however, further confirmation is required through additional voucher specimens.

Pareas orientalis Zhang, Pan & Zhang, sp. nov.

https://zoobank.org/52FEBF33-9BBA-4636-BC3A-A9538CF46E78

Pareas boulengeri (Chen 1991; Zhao et al. 1998). Chresonymy.

Etymology.

Pareas orientalis sp. nov. refers to the new species in eastern China. We recommend designating this new species the Eastern China slug-eating snake and 华东钝头蛇 (Huá Dōng Dùn Tóu Shé).

Type materials.

Holotype : • An adult male (Fig. 7, AHU2024051501) from the Fengteng Village (29.5992°N, 117.9743°E; elevation 249 m a.s.l.), Xiuning County, Huangshan City, Anhui Province, China, was collected by Lei Yu and Muyao Zhang on 15 May 2024.

Figure 7. 

Pareas orientalis sp. nov. in preservative (AHU2024051501). A. Dorsal view; B. Ventral view; C. Right lateral view of the head; D. Left lateral view of the head; E. Ventral view of the head; F. Dorsal view of the head. Scale bars: 10 mm.

Paratypes : Eight specimens (3 females and 5 males) were collected from Huangshan City and its surrounding areas. • One adult male specimen (AHU2024051502) was collected on the same day and at the same location as the holotype. Additionally, • two females (AHU2015062201, AHU2015082001) and three males (AHU2020061201, AHU2024072201, AHU2024072202) were collected in Huangshan City. Furthermore, • one adult female specimen (AHU2019071201) was obtained from Jing County, Huangshan City, • one adult male (AHU2021101501) was collected from Chunan County, Hangzhou City, Zhejiang Province.

Diagnosis.

Pareas orientalis sp. nov. can be distinguished from its congeners based on the following morphological characteristics: (1) medium body size (TL 311–452 mm, n = 3 females; 420–524 mm, n = 6 males); (2) yellow–brown body coloration with many irregular black horizontal stripes; (3) the length of suture between internasals subequal to that between the prefrontals, with prefrontal bordering orbit; (4) the frontal subhexagonal to diamond-shaped with lateral sides converging posteriorly; (5) one subocular, one preocular, one loreal, and only tip bordering eye; (6) the prefrontal contacts the eye, and there one subocular scale fused with postocular scale; (7) 7–8 supralabial scales, 9 infralabial scales; (8) rows of 15-15-15 dorsal scales, three rows of mid-dorsal scales slightly keeled at the midline, median vertebral scale row not enlarged; (9) 175–187 ventrals, 69–75 subcaudals, divided, with a single cloacal plate; (10) prefrontal and postfrontal bones do not exhibit contact, asymmetric teeth number in maxilla, palatine, pterygoid, and dentary bones (MX 6–7/5–6, PAL 3/3–4, PT12–14/12–13, DT 17–19/21–23); (11) dorsal surface of the head exhibits a dense arrangement of small, black spots; two black longitudinal stripes extend posteriorly, behind the parietal and supraocular scales, converging into a prominent black stripe in the neck region; a slender black horizontal line is present on the lateral aspect of the head, posterior to the eye and extending toward the corner of the mouth.

Holotype description.

An adult male with a 515 mm total length (SVL 405 mm, TaL 110 mm); relatively short tail (TaL/TL ratio 0.21); body slender, slightly compressed; head distinct from neck with a wide and blunt snout, projecting beyond lower jaw; head elongate, clearly distinct from neck; snout round in dorsal view; eye slightly enlarged, pupil vertical and slightly elliptical; rostral approximately as wide as high, slightly visible from above; nasal undivided; internasal elongated; prefrontal, approximately trapezoidal, bordering orbits; frontal shield-shaped, slightly longer than wide; parietals large, longer than wide, gradually narrows posteriorly, median suture approximately equal to length of frontal; one loreal, in contact with eye; one triangular preocular scale; one subocular scale that converges with the postocular scale, extending from the posterior aspect of the eye to the ventral corner of the eye; temporals 2+3/2+3; 8/8 supralabial scales; 9/9 infralabials; three chin-shield pairs; dorsal scales are mostly smooth, with three rows of mid-dorsal scales slightly keeled at the midline and arranged in 15 rows, while dorsal scales are not enlarged; 182 ventral scales; 72 subcaudal scales, paired; single cloacal plate. Prefrontal and postfrontal bones do not exhibit contact, asymmetric teeth number in maxilla, palatine, pterygoid, and dentary bones (MX 7/6, PAL 3/4, PT14/12, DT . 8/23).

Coloration in life.

Dorsal surface of the head exhibits a dense arrangement of small, black spots; two black longitudinal stripes extend posteriorly, behind the parietal and supraocular scales, converging into a prominent black stripe in the neck region. A slender black horizontal line is on the lateral aspect of the head, posterior to the eye and extending toward the corner of the mouth. The dorsal surface is distinguished by a yellowish-brown coloration featuring 52 irregular and discontinuous black horizontal stripes. In contrast, the ventral side displays a grayish-white coloration, embellished with scattered fine black spots.

Coloration in preservative.

In its preserved state, the specimen’s coloration resembles that of its living condition. The yellowish–red dorsal surfaces of the head and body fade to a pinkish–brown hue, indicating a significant loss of vibrant pigmentation. Notably, the black stripes along the sides of the body and tail remain distinct, maintaining their contrast despite fading in other regions. The pinkish-yellow coloration of the belly and the ventral surfaces of the head and tail diminishes to a pinkish-white, suggesting further pigment degradation. Additionally, the iris transforms to a grayish-black, while the pupil becomes white, reflecting further changes in pigmentation attributable to the preservation process.

Variation.

The nine specimens exhibited nearly identical morphological characteristics. The fundamental statistics for the morphological measurements are presented in Suppl. material 1: tables S2, S3. The quantity of posterior temporals ranged from two to three. The number of vertical black stripes on each side of the body ranged from 45 to 58, while the iris color in the paratypes varied from reddish-yellow to yellow.

Distribution and habitat.

Based on the available distribution data, this species is hypothesized to be predominantly located in southern Anhui, southern Jiangsu, northern Jiangxi, and Zhejiang (Fig. 1). It inhabits mountainous regions, frequently residing near low shrubs adjacent to streams in low-altitude areas, and primarily feeds on slugs and snails.

Comparison.

Comparisons between the new species and its congeners are summarized in Table 3. Pareas orientalis sp. nov. and P. dabieshanensis sp. nov. were previously classified as P. boulengeri. However, P. orientalis sp. nov. exhibits distinct morphological characteristics. Pareas orientalis sp. nov. can be differentiated from P. dabieshanensis sp. nov. (Figs 5, 6) by the presence of one preocular scale (vs. no preocular scale), one subocular fused with the postocular (vs. two subocular scales, one of which is fused with the postocular scale), and three rows of middorsal scales keeled at the midline (vs. smooth at midbody), fewer teeth number in maxilla bone (MX 5–7 vs. 5), and more teeth number in pterygoid bone (PT12–14 vs. 9–11). The distinction between P. orientalis sp. nov. and true P. boulengeri is characterized by one preocular scale (vs. no such scale), more subcaudals (69–75 vs. 57–66), and fewer teeth number in maxilla bone (MX 5–7 vs. 4–5).

Table 3.
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The diagnostic features of scalation and dorsal coloration of Pareas dabieshanensis sp. nov. and Pareas orientalis sp. nov. are compared with those of the currently recognized species within the genus Pareas. Exceptional values are indicated in parentheses. The following abbreviations are utilized: TL max. = maximum total length; SPL = supralabials; IFL = infralabials; Preoc = number of preoculars; SoO = number of sunoculars; PoO = number of postoculars; TEP = number of temporals; Loreal = loreal-eye contact; DSR = dorsal scale rows; Ven = ventral scales; Sc = subcaudals; enlarged = median vertebral scale row slightly enlarged; keeled = median scale rows slightly keeled; color = dorsal coloration.

ID Species max. TL SPL IFL Preoc SoO PoO TEP Loreal DSR VEN SC enlarged keeled color source
1 P. dabieshanensis sp. nov. 517 7–8 9 0 2 Fused 2+3 yes 15 184–187 68–74 0 0 yellow-brown 1
2 P. orientalis sp. nov. 524 7–8 9 1 Fused Fused 2+2 or 2+3 yes 15 175–187 69–75 0 3 yellow-brown 1
3 P. abros 565 9 8–9 1 3 2 3+3 no 15 180–184 83–95 1 9–11 yellow-brown 2
4 P. andersonii 481 9 7–8 0 1 1 2 no 15 141–162 35–47 0 5–9 grayish 3
5 P. atayal 560 9 7–9 1 Fused Fused 2+3 or 2+4 no 15 174–188 71–77 2 7 yellow-brown 4
6 P. baiseensis 579 8 9 1 2–3 1 2 + 3 or 3 + 3 no 15 187–191 89–97 1 5 yellow-brown 5
7 P. berdmorei 770 9 7–9 1–2 1–3 0–2 3 + 4 or 3 + 3 no 15 162–187 57–89 1–3 3–13 yellow-brown 2
8 P. boulengerii 566 7–8 9 0 Fused Fused 2+2 or 2+3 yes 15 175–188 57–66 0 0 yellow-brown 1
9 P. carinatus 610 7–9 7–9 2 1 or 2 2 2+3 no 15 172–183 66–89 3 9–13 yellow-brown 4, 8
10 P. chinensis 682 7–9 7–9 1 1 1 2+3 no or only tip 15 166–192 56–84 1 3 yellow-brown 6, 7, 8
11 P. dulongjiangensis 488 6—7 7—9 0 Fused Fused 2+3 or 2+2 yes 15 182 76 3 5 yellow-brown 9
12 P. formosensis 617 7–8 7 1 1 1 2+3 or 2+2 no 15 163–181 70–80 3 yellow-brown 4, 8
13 P. geminatus 566 6–8 8 1 Fused Fused 1–2 no 15 170–188 75-91 1 3–5 yellow-brown 8
14 P. guanyinshanensis 540 7–8 6–8 1 Fused Fused 2+2 or 2+3 or 2+4 no 15 189–192 72–89 1 5 yellow-brown 9
15 P. hamptoni 483 7–8 6–9 1 1 or Fused 1 or Fused 1+2 or 2+3 no 15 185–195 91–99 1–3 5–9 yellow-brown 8
16 P. iwasakii 700 NA 9–11 1 1 1 3+4 or 2+3 yes 15 190–193 76–84 1 5–7 yellow-brown 4, 10, 11
17 P. kaduri 694 7 7 1 1 2 2+3 no 15 160–183 52–70 1 8 yellow-brown 12
18 P. komaii 600 7 7 1 1 1 2+3 no 15 162–182 60–76 3 9–13 yellow-brown 4, 11
19 P. kuznetsovorum 639 7 7–8 1 2 1 3+4 no 15 167 87 1 0 yellow-brown 2
20 P. macularius 517 7 6–8 1 1 1 2+3 no 15 151–173 39–53 0 5–11 grayish 8,19
21 P. margaritophorus 394 6–9 5–9 1 1 1 2+3 no 15 133–160 35–54 0 0 grayish 8,19
22 P. modestus 357 7 7 1 1 1 2+3 no 15 151–159 35–46 0 3–5 grayish 8,19
23 P. monticola 750 7–8 7–8 0 1 1 2+3 yes 15 178–199 69–90 1–3 0 yellow-brown 8,12
24 P. niger 585 6–7 8–9 1 Fused Fused 2+3 no 15 167–173 54–61 3 3–9 yellow-brown 13
25 P. nigriceps 520 7 7 1 Fused Fused 1+2 or 1+3 yes 15 175–184 73–77 1 9 brownish-black 8,14
26 P. nuchalis 678 7–8 6–8 1 1–3 1–2 3 + 4 or 3 + 3 no 15 201–220 102–120 1–3 0 brown 8
27 P. stanleyi 650 7–8 7–8 0 1 1 2 + 2 or 2 + 3 yes 15 151–160 48–64 0 13 yellow-brown 8,13
28 P. temporalis 578 8–9 8–9 2–3 2 2–3 4+3 no 15 191 92 3 all yellow-brown 15
29 P. tigerinus 543 7 7 1 Fused Fused 1+1 or 1+2 no 15 160–171 62-64 1 3–5 yellow-brown 16
30 P. victorianus 487 7 6–7 0 Fused Fused 2+3 yes 15 164 58 1 8 yellow-brown 17
31 P. vindumi 657 6 6 0 Fused Fused 2+3 yes 15 178 61 0 0 yellow-brown 17
32 P. xuelinensis 576 7 7—9 1 Fused Fused 2 + 2 or 2 + 3 no 15 182–188 87–93 0 0–5 yellow-brown 18
33 P. yunnanensis 586 6–8 6–8 1–2 Fused Fused 1+2 or 2+2 or 2+3 yes 15 169–175 59–65 1 5–7 yellow-brown 17

Note: Sources are denoted as follows: 1 = This study; 2 = Poyarkov et al. (2022); 3 = Vogel et al. (2020); 4 = You et al. (2015); 5 = Gong et al. (2023); 6 = Jiang (2004); 7 = Vogel (2015); 8 = Ding et al. (2020); 9 = Liu et al. (2024); 10 = Ota et al. (1997); 11 = Oskyrko et al. (2024); 12 = Bhosale et al. (2020); 13 = Wang et al. (2020); 14 = Guo and Zhao (2004); 15 = Le et al. (2021); 16 = Liu et al. (2023a); 17 = Vogel et al. (2020); 18 = Liu and Rao (2021).

Given that P. orientalis sp. nov. and P. dabieshanensis sp. nov. exhibit morphological similarities, with most morphological features relatively comparable and their body colors largely indistinguishable, the primary differences lie in the presence or absence of preocular scales, the number of subocular scales, and the presence of keeled mid-dorsal scales at the midline of the body. As P. dabieshanensis sp. nov. was extensively compared with other species in the preceding section of the article, redundant elements have been excluded here.

Pareas orientalis sp. nov. can be distinguished from P. andersonii, P. macularius, P. margaritophorus, and P. modestus by a yellow–brown dorsum (yellow–brown vs. grayish). P. orientalis sp. nov. can be distinguished from P. abros, P. atayal, P. baiseensis, P. berdmorei, P. carinatus, P. formosensis, P. geminatus, P. guanyinshanensis, P. hamptoni, P. kaduri, P. komaii, P. kuznetsovorum, P. niger, P. nuchalis, P. temporalis, P. tigerinus, and P. xuelinensis by the presence of a loreal scale in contact with the eye (vs. the loreal scale not contacting the eye).

Pareas orientalis sp. nov. can be distinguished from P. chinensis, P. iwasakii, P. monticola, and P. stanleyi by suboculars fused with postoculars (vs. separated).

Pareas orientalis sp. nov. can be distinguished from Pareas dulongjiangensis, P. victorianus, and P. vindumi by the presence of one preocular scale (vs. no preocular scale).

Pareas orientalis sp. nov. differs from P. nigriceps and P. yunnanensis by having more infralabial scales (9 vs. 6–8).

Discussion

The phylogenetic analysis conducted by Poyarkov et al. (2022) supports the classification of the genus Pareas into six distinct species groups: P. carinatus, P. nuchalis, P. chinensis, P. hamptoni, P. monticola, and P. margaritophorus. The findings of the current study indicate that P. boulengeri, P. dabieshanensis sp. nov., and P. orientalis sp. nov. are members of the P. chinensis species group. Notably, P. dabieshanensis sp. nov. possesses two subocular scales, aligning with the characteristics of P. baiseensis but contradicting the diagnostic features attributed to the subgenus Eberhardtia, as outlined by Poyarkov et al. (2022). Consequently, as proposed by Gong et al. (2023), we recommend revising the diagnostic parameters by removing the single thin elongated subocular characteristic.

Pareas boulengeri was previously believed to have a broad distribution across various regions in China, encompassing 16 provinces: Anhui, Chongqing, Henan, Hunan, Gansu, Guangdong, Guangxi, Guizhou, Fujian, Jiangsu, Jiangxi, Shaanxi, Sichuan, Yunnan, and Zhejiang (Zhao et al. 1998; Chen et al. 2006; Guo and Deng 2006; Zhao 2006). The Pareas genus, characterized by its ancient origins and limited migratory capabilities, exhibits a notable degree of limited variation in morphological traits, with relatively minor distinctions among species, particularly in coloration and scale number (You et al. 2015; Poyarkov et al. 2022). Consequently, species once classified as P. boulengeri may have been misidentified due to the close morphological similarities among related species. Therefore, further molecular investigations of P. boulengeri, which is currently identified in the provinces of Gansu, Guangdong, Fujian, and Shaanxi, are crucial for clarifying existing taxonomic ambiguities.

Additionally, it is important to address the three species sites depicted in Fig. 1 that lie outside the suspected distribution ranges of the identified species. Originally classified as P. boulengeri, these sites were not categorized into any of the three species in this study due to the absence of mitochondrial gene sequences from local specimens. Given the subtle morphological differences among Pareas species, these records may represent misidentifications of Pareas taxa. However, they also present the possibility of being P. orientalis or even an undescribed species, particularly since their geographic locations fall outside the currently recognized distribution boundaries. This discrepancy underscores the need for cautious interpretation of distributional data, as misidentifications in GBIF uploads could potentially obscure the true ecological niche of these species. We encourage future surveys to prioritize field validation of these outlying records through comprehensive sampling, morphological re-examination, and genetic sequencing. Such efforts will be critical for determining whether these sites represent range extensions, misclassifications, or the presence of cryptic species—thereby refining our understanding of Pareas distribution dynamics and enabling more accurate delineation of species ranges in subsequent studies.

Identifying P. dabieshanensis sp. nov. and P. orientalis sp. nov. has increased the total recognized Pareas species to 33, with 27 documented in China (Uetz et al. 2025). Currently, three species belonging to the genus Pareas have been identified in Anhui Province: P. chinensis, P. dabieshanensis sp. nov., and P. orientalis sp. nov. (Chen 1991; Pan et al. 2014). In Anhui Province, our collections included P. dabieshanensis sp. nov. and P. orientalis sp. nov., but not P. chinensis. This suggests that previous records of P. chinensis in Anhui may have resulted from misidentification of P. orientalis sp. nov. Further survey efforts are necessary to enhance our understanding of the distribution of blunt-headed snakes in Anhui Province and to elucidate the diversity of the Pareas genus in this area.

However, the results of this study indicate that Pareas boulengeri is restricted to the provinces of Guizhou, Sichuan, Hubei, Yunnan, and Guangxi in southwestern China, while P. dabieshanensis sp. nov. is confined to the Dabie Mountain region in central China. Concurrently, P. orientalis sp. nov. occurs in southern Anhui, southern Jiangsu, northern Jiangxi, and Zhejiang in eastern China. Notably, the distribution ranges of these three species do not overlap. It is particularly noteworthy that P. dabieshanensis sp. nov. and P. orientalis sp. nov. are separated solely by the Yangtze River. Previous research has established that the river, as a significant hydrological system, acts as a natural barrier that has contributed to the evolutionary isolation of species (Carmichael et al. 2001; Wang et al. 2015; Zhang et al. 2023). Hence, the Yangtze River, as a natural barrier and ecological isolation zone, has had a profound impact on the evolution and diversity of species. Similar patterns have been observed in closely related species, such as Achalinus dabieshanensis and A. huangjietangi, which are geographically divided by the Yangtze River (Zhang et al. 2023), as well as P. hamptoni and P. guanyinshanensis, which are separated by the Red River (Liu et al. 2024). Consequently, the observed distribution pattern may be attributed to the distinctive topographic and climatic characteristics present on either side of the Yangtze River. Future research on the comparative phylogeography of these species could be conducted to investigate the underlying mechanisms of their formation.

On the other hand, studies on the asymmetric mandibular teeth of Pareas snakes and their mollusc prey have highlighted a novel aspect of the evolution of these snakes (You et al. 2015). Although the sample size is limited, preliminary evaluation of the dentition asymmetry index showed substantial variation among the specimens evaluated in this study (Suppl. material 1: table S3). Further studies on the correlation between dentition asymmetry and prey preference, using a larger sample size, will provide insight into dietary resource partitioning and niche differentiation between these species.

Scientific field survey permission information

This study was approved by the Institutional Animal Care and Use Committee of the School of Life Sciences, Anhui University (project number: IACUC (AHU)-2023-060; approval date: 17 November 2022). The management offices of the Yaoluoping National and Wanfoshan Provincial Nature Reserves granted permission for field surveys and species collection in the Dabie Mountains.

Funding

This study was supported by the Comprehensive Monitoring Station for National Ecological Quality in the Dabie Mountains (Forest): Ecological Monitoring for the Years 2024–2025 (ZF2024-18-1376).

Acknowledgments

We would like to express our sincere gratitude to Dr. Jing-song Shi at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Chinese Academy of Sciences, for his invaluable contributions. We also extend our appreciation to Dr. Zhong Chen of Anhui University for providing two snake specimens that were essential to our study. Additionally, we would like to thank Professor Chen Hong from Liupanshui University for supplying three snake specimens. Furthermore, we wish to acknowledge the significant support of Wen-gang Li, Mu-yao Zhang, Fei Hong, and Chang-ting Lan throughout this research. We are also grateful for the assistance provided by Jun Ding and Laisheng Huang from the Wanfoshan Provincial Nature Reserve during the fieldwork. Our acknowledgments further extend to Jun Chu, Yong Chu, Xinjian Wang, and Xinxiang Li from the Yaoluoping National Nature Reserve, as well as Faguang Pu from the Tianma National Nature Reserve, for their contributions.

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Supplementary material

Supplementary material 1 

Supplementary information

Cai-wen Zhang, Shi-hang Xu, Tao Luo, Chong Liu, Lei Yu, Jiang Zhou, Tao Pan, Bao-wei Zhang

Data type: docx

Explanation note: Text.

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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