Pareas orientalis Zhang, Pan & Zhang sp. nov.

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, AHU 2024051501) 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.

Paratypes: Eight specimens (3 females and 5 males) were collected from Huangshan City and its surrounding areas. • One adult male specimen (AHU 2024051502) was collected on the same day and at the same location as the holotype. Additionally, • two females (AHU 2015062201, AHU 2015082001) and three males (AHU 2020061201, AHU 2024072201, AHU 2024072202) were collected in Huangshan City. Furthermore, • one adult female specimen (AHU 2019071201) was obtained from Jing County, Huangshan City, • one adult male (AHU 2021101501) 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, PT 12–14 / 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, PT 14 / 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 S 2, S 3. 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 (PT 12–14 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).

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. (2023 a); 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).