Plagiopholis acuta Xu, Ma, & Cai sp. nov.

Holotype.

QHU 2024009, adult male, collected by the team of Lifang Peng in August 2024 from Xinshao County, Shaoyang City, Hunan Province, China (27.4533°N, 111.7558°E, 530 m a. s. l.)

Paratypes.

QHU 2024010 (adult female), QHU 2024011 (adult male), with the same collected information as the holotype; QHU 2024044 (adult female) collected by the team of Lifang Peng in October 2024, from the same locality as the holotype.

Other material examined.

QHU 2024012, juvenile, an offspring hatched in captivity on 16 September, 2024, from the egg laid by the female specimen QHU 2024010.

Diagnosis.

Plagiopholis acuta sp. nov. can be differentiated from other taxa in the genus Plagiopholis by the following combination: (1) no loreal, posterior nasal forming a suture with the single preocular; (2) two postoculars; (3) temporals 2 + 2 (rarely 2 + 1); (4) 6 (rarely 7) supralabials, the 3 rd and 4 th entering the eye; (5) 6 (rarely 5) infralabials; (6) maxillary teeth 17–18 in males and 15–17 in females; (7) dorsal scale smooth and rows 15-15 - 15; (8) ventral scales 114–115 in males and 115–121 in females; (9) anal entire; (10) subcaudal scales 29–30 in males and 24–25 in females; (11) longer tail length of 51–52 mm (mean 51.5 mm) in males and shorter tail length of 25–43 mm (mean 34 mm) in females; (12) larger TAL / SVL ratio of 0.18–0.19 (mean 0.19) in males and lower TAL / SVL ratio of 0.11–0.14 (mean 0.12) in females; (13) hemipenis half divided, bilaterally symmetrical, the truncus spinulate throughout; (14) a wide, black-brown blotch is present on the neck, often pentagonal or sub-annular shaped, across 4–6 dorsal scale rows; (15) dorsal surface of the body is brick-red, with some dorsal scale edges black, forming a faint reticulated pattern.

Description of the holotype.

Measurements and scalation. An adult male with TL 313 mm (SVL 262 mm and TAL 51 mm); tail relatively short, TAL / TL ratio of 0.16, and TAL / SVL ratio of 0.19; body slender and small; head slightly distinct from the neck, HL 12.8 mm, HW 7.8 mm, HH 6.0 mm; eye moderate, ED 2.12 mm; rostrum triangular, wider than high, slightly visible from above; snout relatively short, ESD 3.7 mm; internasals and prefrontals paired; frontal haxagonal, longer than wide, a little shorter than the parietals; PRO 1 / 1, PO 2 / 2; loreal absent; TEMP 4, arranged in two rows (2 + 2 / 2 + 2); SL 6 / 6, the 3 rd and 4 th entering the eye, the 5 th and 6 th largest; chin shields in 2 pairs, the anterior pair longer than posterior one and in contact with the mental; IL 6 / 6, the 1 st to 3 rd touching the first pair of chin shields. DSR 15-15 - 15, all smooth, including the outermost row on both sides; VS 115, SC 30, CP entire.

Dentition. Maxillary teeth 18 / 17, without diastema; except for the first 3 being smaller, the rest are nearly equal in size.

Coloration in life. In life, dorsal surface of the head is deep reddish-brown, with small black-brown spots scattered along the sides; the supralabials are creamy-white with black edges on both sides. Ventral surface of head cream-white, the edges of partial scales have irregular black-brown patches. A wide, black-brown collar is present on the neck, across 5 dorsal scale rows. Dorsal surface of the body is brick-red, with some dorsal scale edges black, forming a faint reticulated pattern. The ventral and subcaudal scales uniform pale yellow (Fig. 7).

Coloration in preservation. In preservation, the coloration still resembles the specimen in life, except that the coloration of dorsum further deepens, and the ventral surface of head becomes pale yellow (Figs 8, 9).

Variation.

The main morphological characters of Plagiopholis acuta sp. nov. are listed in Table 4. The paratypes exhibit a similar morphological pattern as the holotype, but there is a pronounced sexual dimorphism: compared to females, the examined males have a significantly longer tail, TAL / TL ratio of 0.15–0.16 and TAL / SVL ratio of 0.18–0.19 (vs. TAL / TL ratio of 0.10–0.12 and TAL / SVL ratio of 0.11–0.14 in females), fewer ventrals (114–115 vs. 115–121 in females), more subcaudals (29–30 vs. 24–25 in females), and more maxillary teeth (17–18 vs. 15–17 in females).

Hemipenis. Description based on the everted left organ of the male paratype QHU 2024011 (Fig. 10). When fully everted, the hemipenis is Y-shaped, bilaterally symmetrical, extends to SC 7, and bifurcates at lower 4 / 7. Both sulcate and asulcate surfaces densely ornamented with spinules, spines, or calyxes. Truncus spinulate throughout, branches divided into spine and calyx areas; a well-developed, calcareous basal hook is present on the asulcate surface of each branch.

Spiny area characterized by medium-size, dense spines, gradually decrease in size distally, reaching nearly half of the branches, then merging into thorny calyces. The calyx area extends to the distal end of each branch. The sulcus spermaticus is divided, extending centrifugally to the tip of each branch, and the sulcus lips are visible and slightly raised.

Etymology.

The specific epithet “ acuta ” means “sharp,” referring to the large, pointed basal hooks on the hemipenis of this species. Based on the type locality, Xinshao County, Hunan Province, we suggest “ Hunan Mountain Snake” as its English common name and “ 湖南颈斑蛇 (Hu ́ Na ́ n Ji ̌ ng Ba ̄ n She ́) ” as its Chinese common name.

Distribution and natural history.

Specimen QHU 2024010 was a gravid female collected on August 7, 2024, and then kept in captivity under laboratory conditions at Qinghai University. It was housed in a 60 cm × 40 cm reptile terrarium with a substrate layer of approximately 3 cm of coarse peat soil. Humidity was maintained by providing a water dish and regular misting. On 11 August, the female laid five eggs, with an average length of 21 mm. The eggs were incubated in a moist mixture of coarse vermiculite and perlite at a constant temperature of 27 ° C. After five days of incubation, candling with a flashlight revealed clear signs of embryonic development in only two eggs, while the remaining three showed no visible signs of development. After one week, the undeveloped eggs became moldy and shriveled. During the remainder of the incubation period, one of the two fertilized eggs failed to develop successfully. On September 16, the other one hatched (specimen QHU 2024012), measuring approximately 92 mm in length and weighing 1 g. However, it exhibited some deformities and morphological abnormalities (Table 4, Fig. 11). The first shedding occurred on September 25, and then the snake died on September 28. Based on the feeding and incubation results, we infer that this species may be better adapted to mid-elevations below 2000 m and relatively cool environments. The observed deformities may have been caused by high-altitude conditions or elevated temperatures during transportation and incubation.

Plagiopholis acuta sp. nov. has currently only been discovered in Xinshao County of Shaoyang City, Hunan Province. This area belongs to the mid-subtropical monsoon humid climate zone, characterized by distinct four seasons, abundant sunlight and heat, plentiful rainfall, with the rainy season coinciding with the hot season (Zheng et al. 2013). This new species is most probably distributed within mid-subtropical evergreen broad-leaved forests at an altitude of 530 m.

Comparisons.

Plagiopholis acuta sp. nov. can be separated from P. styani as follows: (1) fewer maxillary teeth, 17–18 in males and 15–17 in females (vs. 20–21 in males and 18 in females); (2) tail relatively longer in males, and shorter in females (TAL / SVL ratio of 0.18–0.19, mean 0.19 vs. 0.15–0.17, mean 0.16 in males, and 0.11–0.14, mean 0.12 vs. 0.12–0.15, mean 0.14 in females); and (3) The truncus of the hemipenis spinulate throughout (vs. smooth). A detailed comparison between the new subspecies and its congeners is summarized in Table 5.

Plagiopholis acuta sp. nov. can be easily separated from P. blakewayi, P. nuchalis, and P. delacouri by having TEMP 2 + 2 (vs. 0 / 1 + 1 in P. blakewayi, 1 + 2 in P. nuchalis and P. delacouri) and different body coloration. Moreover, it can also be separated from P. blakewayi due to the more supralabials (6 vs. 5); and from P. nuchalis due to the fewer maxillary teeth in females (15–17 vs. 20–22) and the absence of the loreal (vs. loreal present).