Achalinus panzhihuaensis Hou & Wang & Guo & Chen & Yuan & Che 2021, sp. nov.

Achalinus panzhihuaensis sp. nov.

(Figs. 3 and 4)

Holotype. KIZ 040189, adult male, collected by Benfu Miao and Kai Wang on 10 May 2018 from Hongbao Village (27.00°N, 101.53°E), Yanbian County, Panzhihua, Sichuan Province, China.

Diagnosis. Achalinus panzhihuaensis sp. nov. can be distinguished from recognized congeners by a combination of the following characters: (1) TaL/ToL 24.6% in the single male; (2) two nasal scales in contact with each other behind the rostral; (3) internasal absent; (4) loreal rectangular; (5) supralabials 6; (6) postocular single and small; (7) temporals 2+2+3, anterior pair elongated, upper one smaller, only uppermost in contact with eye; (8) infralabials 6; (9) mental in contact with first pair of chin shields, fully separating first pair of infralabials; (10) dorsal scales 23–23–19 rows; (11) ventrals 160; (12) subcaudals 73, unpaired; (13) precloacal scale entire; (14) maxillary teeth 28; and (15) all scales iridescent with metallic luster, brown dorsally, with single indigo-colored vertebral line.

Description of holotype. Body size small, total length 257 mm (SVL 194 mm, TaL 63 mm); tail long, 24.6% total length; body slender, cylindrical in cross section. Head slightly distinct from neck, HL 7.8 mm; eye small, pupil vertically subelliptic. Rostral small, triangular, invisible from above; nasal divided, each half in contact with each other; internasal absent; prefrontals paired, suture length 2.1 mm; frontal pentagonal, slightly wider than long, pointed posteriorly; single pair of parietals; loreal pentagonal, tip pointing anteriorly, longer (LeL: 1.2 mm) than high (HiL: 0.8 mm), LeL/HiL 150.0%; supraocular single, in contact with loreal, prefrontals, frontal, parietals, and superior anterior temporals. Temporals in three groups, 2+2+3; superior one of anterior most pair triangular, small, inferior one much larger, elongated, in contact with fourth and fifth supralabials and parietal; the middle pair, superior one parallelogram, small, inferior one much larger, elongated, in contact with sixth supralabials and three posterior temporals; superior most one of last trios biggest, size gradually decreases inferiorly; supralabials six, first one smallest, fourth and fifth in contact with eyes, sixth longest. Mental arc-shaped, in contact with first pair of chin shields; three pairs of chin shields, first pair in fan-shaped, remaining ones of second and third pairs in unequilateralquadrilateral shape. Infralabials six, first pair not in contact with each other, first three in contact with anterior-most pair of chin shields, third and fourth infralabials in contact with middle pair.

Dorsal scales elliptical, 23–23–19 rows, medial 6–11 rows distinctly keeled, remaining outer rows smooth. Ventrals 160, rounded laterally; subcaudals 73, unpaired; precloacal entire.

Coloration: In life, all scales are weakly iridescent with metallic luster. Dorsum is purplish brown. The vertebral and three paravertebral rows of dorsal scales are darker indigo, which form a darker longitudinal vertebral stripe extending from the posterior margin of the parietals to the tip of tail. Ventral surface of the body is greyish white, and the subcaudal region is purplish brown.

In preservative, all scales are still iridescent. Coloration becomes darker after preservation. The dorsum becomes dark grey, and the vertebral stripe turns black. The ventral surface of the body becomes greyish brown, and the ventral tail is dark greyish brown.

Comparisons. A. panzhihuaensis sp. nov. is most similar to its sister species A. meiguensis, in which both species have divided nasal scales in contact with each other, no internasal, a single postocular, 6 supralabials, 6 infralabials, mental in contact with first pair of chin shields, and fully separated first pair of infralabials. However, the new species can be diagnosed readily from A. meiguensis by having more subcaudals (SC 73 vs. 39–60), more ventrals in male (VEN 160 vs. 146–155), and more DSRM (23 vs. 19–21) (Table 4).

Achalinus panzhihuaensis sp. nov. can be easily distinguished from A. ater, A. emilyae, A. formosanus Boulenger, A. hainanus Huang, A. jinggangensis Zong & Ma, A. juliani, A. niger Mahi, A. pingbianensis Li, Yu, Wu, Liao, Tang, Liu & Guo, A. rufescens Boulenger, A. spinalis Peters, A. tranganensis Luu, Ziegler, Ha, Lo, Hoang, Ngo, Le, Tran & Nguyen, A. timi, A. yunkaiensis, A. werneri Van Denburgh and A. zugorum Miller, Davis, Luong, Do, Pham, Ziegler, Lee, De Queiroz, Reynolds & Nguyen, by having divided nasal scales in contact each other behind the rostral (vs. separated), mental in contact with the first pair of chin shields (vs. separated), first pair of infralabials separated from each other (vs. in contact), as well as an absence of internasal (vs. present), and by the presence of a small postocular (vs. absent). Furthermore, the new species differs from A. jinggangensis, A. pingbianensis, A. timi and A. formosanus by having loreal separated from prefrontal (vs. fused); and from A. emilyae, A. hainanus and A. rufecens by having more infralabials (6 vs. 5).

Natural history and distribution. The holotype was found on a montane road at night. The surrounding habitat was of secondary forest of evergreen broadleaf forest with shrubs and vines (Fig. 5). According to locals, road-killed individuals are somewhat common in the summer. At the type locality, the species is sympatric with Diploderma swild Wang, Wu, Jiang, Chen, Miao, Siler, Che, 2019, Lycodon cf. gongshan Vogel, Luo, 2011, Hebius yanbianensis Liu, Zhong, Wang, Liu, Guo, 2018, Ptyas nigromarginata (Blyth, 1854), Megophrys platyparietus (Yang, Rao, 1997), and Odorrana sp.. The new species is currently only known from the type locality in Panzhihua, Sichuan Province, China (Fig. 1).

Etymology. The specific epithet “ panzhihuaensis ” is named after the type locality of the new species, Panzhihua, Sichuan Province, China. We propose “Panzhihua Odd-scaled Snake” as its common English name and “ Ẓ枝 AEñffi ” (Pinyin: Pan Zhi Hua Ji She) as its Chinese common name.