Rhabdophis angeli ( Bourret 1934 )

Rhabdophis angeli ( Bourret 1934) View in CoL

( Figs. 1–2 View FIGURE 1 View FIGURE 2 , 4A–C View FIGURE 4 ; Table 2)

Natrix ( Rhabdophis) angeli Bourret, 1934: 151 . Holotype: MNHN-RA-1938.0123, adult female, collected by R. Bourret on January 1, 1929. Type locality: “Tam-Dao, Tong-King ( 60 km au Nord-Est d’Hanoï)”, now Tam Dao National Park, Phu Tho Province, Vietnam.

Rhabdophis angeli View in CoL — Bourret (1935: 4); Bourret (1936: 102); Orlov et al. (2000: 73); Nguyen et al. (2009: 365); Wallach et al. (2014: 633); Poyarkov et al. (2023: 359).

Natrix angeli — Smith (1943: 300).

Rhabdophis guangdongensis Zhu, Wang, Takeuchi & Zhao, 2014: 473 View in CoL View Cited Treatment , Fig. 2A–B View FIGURE 2 , 3A–C View FIGURE 3 . Holotype: SYS r000018, adult female, collected by Y.Y. Wang on May 26, 2008. Type locality: Aizhai Village , Renhua County, Guangdong Province, China ( 4°56'16.58"N, 113°39'57.82"N; altitude 132 m asl)

Rhabdophis guangdongensis View in CoL — Che et al. (2020: 721); Zhu et al. (2020: 108–119); Qin et al. (2023: 107893); Nguyen & David (2023: 224–236, in part); Jiang et al. (2025, Appendix I).

Rhabdophis cf. guangdongensis View in CoL —Poyarkov et al. (2023: 360, in part).

Specimens examined ( n = 4, all from the type locality of Rhabdophis angeli in Tam Dao NP, Phu Tho Province, Vietnam): MNHN-RA-1938.0123 (adult female, holotype) collected on January 1, 1929, by R. Bourret; MNHN- RA-1935.0059 (adult male) collected in 1935 by R. L. Bourret; MNHN-RA-1958.0463 (adult male) collected in 1958 by R. L. Bourret; ROM 34577 About ROM (adult female) collected by N.L. Orlov in 1977 (altitude 900 m asl) .

Referred material from the literature ( n = 6, all from Guangdong Province, China). SYS r00018 ( Holotype of Rhabdophis guangdongensis ) from Aizhai Village, Renhua County ( 4°56'16.58"N, 113°39'57.82"E; altitude 132 m asl) collected by Y.Y. Wang on May 26, 2008 (data from Zhu et al. 2014). SICAU 20160801-91 (adult male) and SICAU 201509013-305 (adult female) from Mt. Wutong, Shenzhen County; ZL-RG-2018-0421 (adult female) from Mt. Nankun, Huizhou County; ZL-RG- 2014-4-10 (adult female) from Mt. Yinping, Dongguan County; and ZL-RG-2017-0423 (adult female) from Mt. Tianjing, Shaoguan County (data from Zhu et al. 2020).

Revised diagnosis. Rhabdophis angeli can be diagnosed by the combination of the following characters: (1) head well distinct from the neck; (2) maxillary teeth 20–23, the posterior-most two or three teeth abruptly enlarged, not grooved, and not separated by diastema from the rest of the series; (3) supralabials six (rarely five), the third and fourth touching the eye; (4) seven or eight infralabials, the first four in contact with anterior chin shields; (5) dorsal scales in 15 rows throughout, feebly keeled, the outer row smooth; (6) ventrals 118–127; (7) subcaudals 38–47; (8) top of head, occiput, and nape (anterior to the black collar) grey; (9) a broad black collar, posteriorly bordered by a reverse V-shaped orange mark on the nape; (10) dorsal surface of body and tail brownish-grey, bearing narrow black cross-bars; (11) body and tail each with two dorsolateral longitudinal brownish-red lines, each line accompanied by a series of white spots within the cross-bars; (12) lips bearing two conspicuous black oblique bands, one below the eye and one behind the eye; (13) ventral surface of head and neck cream-coloured with black spots, gradually becoming entirely black posteriorly; (14) nine to ten pairs of nuchal glands, separated by a diastema from 116–118 pairs of dorsal glands (observed in two specimens); (15) hemipenis bilobed, bearing spines, extending to the level of the 12 th subcaudal; the bifurcation occurs at the level of the 10 th subcaudal (data from Bourret 1934; Zhu et al. 2014, 2020; this study).

Description of the holotype of Natrix ( Rhabdophis) angeli Bourret ( Fig. 1 View FIGURE 1 )

Habitus . Body elongate and cylindrical; head distinct from neck; snout moderately long; eyes large with rounded pupils; tail of moderate length, slender, and gradually tapering.

Body size. SVL 358 mm, TaL 75 mm, TL 433 mm, TaL/TL ratio 0.173.

Body scalation. Dorsal scale rows 15-15-15; dorsal scale rows feebly keeled, the outer most are smooth; 123 ventral scales, laterally slightly angulate; 42 subcaudals, paired and laterally slightly angulate; cloacal plate divided.

Head scalation. Rostral wider than high, triangular, hardly visible from above; posterior rostral scale suture bordering internasals and forming a straight angle in dorsal view; nasal vertically divided by a furrow below and above the nostril; nostril large and lateral, piercing in a completely divided nasal; nasal surrounded by the first two supralabials, rostral, internasal, prefrontal, and loreal; internasals paired, anterior sutures slightly concave in dorsal view, in contact anteriorly with the rostral, and laterally with the nasal, followed by the prefrontal; each internasal slightly wider than long; prefrontals paired, large, subrectangular, and shorter than frontal; each prefrontal in contact with internasals, nasals, loreal, and frontal; supraoculars paired, subrectangularly shaped, posterior end of each scale slightly wider than anterior end; frontal small, hexagonal, shield-shaped, slightly longer than wide, tapering posteriorly; parietals paired, longer than wide; loreal 1/1, higher than longer, not in contact with the eye; preocular 1/1; subocular absent; postoculars 3/3, the uppermost scale slightly larger than the lowermost one; temporals 1+2; supralabials 5/5, the first and second in contact with the nasal, the second in contact with the loreal, and the second and third in contact with the eye, the fourth is the largest; infralabials 7/7, the first to fourth in contact with the anterior pair of chin shields; mental subtriangular in ventral profile, longer than wide; posterior chin shields equal in size relative to anterior shields.

Colouration in preservative: Dorsal surface of the head and body ashy grey; top of head, occiput, and nape uniformly dark grey. A broad, black collar, approximately five dorsal scale rows wide, is present on the nape, posteriorly bordered by a reverse, V-shaped pale yellow zone approximately four scale rows wide. Narrow dorsolateral black cross-bars extend along the body and tail. A longitudinal brownish-red line is present on each side of the body and tail, running parallel to its contralateral counterpart and intersected by a series of white spots within the crossbars. Lips grey, with two distinct black oblique bands: one located below the eye and another situated behind the eye between the fourth and fifth supralabials. The ventral surface of the head and neck is cream-coloured with scattered black spots, gradually becoming entirely black toward the posterior.

Variation (see Table 2 for the details). The longest known female specimen is 559 mm long (ZL-RG 2014-4-10; SVL 475 mm, TaL 84 mm). The longest known male is 435 mm long (SICAU 20160801-91; SVL 341 mm, TaL 94 mm). TaL/TL ratio 0.15–0.22 (without sexual dimorphism).

Body scalation. DSR 15-15-15; VEN 118–127 (males 118–123; females 122–127); SC 38–47, without sexual dimorphism.

Head scalation. SL 6/6, rarely 5/5 ( 1 specimen) or 5/6 ( 1 specimen); IL 8/8, rarely 7/7 ( 2 specimens) or 8/7 ( 1 specimen, unilateral). Loreal present, not touching the eye. PRO 1/1; PTO usually 3/3, rarely 2/2 ( 2 specimens) or 3/2 ( 1 specimen, unilateral). TEM is usually 1+1/1+1, rarely 1+2/1+2 ( 1 specimen) or 1+1/1+2 ( 2 specimens, unilateral). In these rare cases, an additional small posterior temporal is present, which may be counted either as 1+2 or as 1+1+1 depending on the counting system; here it is treated as 1+2.

Dentition. Based on two specimens: MNHN-RA-1935.0059 data from Bourret (1934) and SYS r00018 data from Zhu et al. (2014): a total of 20–23 maxillary teeth, the posterior-most two or three maxillary teeth strongly enlarged, not separated by diastema from the rest of the series.

Main characters of pattern (data from Bourret 1934, 1935; Zhu et al. 2014, 2022; and Fig. 4A–C View FIGURE 4 ). Dorsal surface brownish-grey; top of head, occiput, and nape grey; a broad black collar, approximately five scale rows wide, posteriorly bordered by a reverse V-shaped orange zone about four scale rows wide on the nape; 38–44 pairs of narrow dorsolateral black cross-bars along the body and 15 pairs on the tail; body and tail each bearing a longitudinal brownish-red line running parallel to the contralateral line, accompanied by a series of white spots within the crossbars; lips light grey, with two conspicuous black oblique bands, one situated below the eye and the other extending from behind the eye between the last two supralabial scales; ventral surface of the head and neck cream coloured with black spots, gradually becoming entirely black posteriorly.

Comparisons. Rhabdophis angeli View in CoL is phylogenetically placed within the Rhabdophis nuchalis View in CoL species group and is morphologically most similar to other members of the R. nuchalis View in CoL complex, including R. chiwen View in CoL , R. hmongorum View in CoL , R. kaiyuanensis View in CoL , R. leonardi View in CoL , R. nuchalis View in CoL , R. pentasupralabialis View in CoL , and R. swinhonis View in CoL . Therefore, comparative analyses with these seven species are the most relevant for diagnostic purposes. The main morphological characters distinguishing Rhabdophis angeli View in CoL from these congeners are summarised in Table 3 and illustrated in Fig. 4 View FIGURE 4 .

Rhabdophis angeli is distinguished from R. chiwen (endemic to Sichuan Province, China) by having a lower number of VEN (118–127 vs. 151–159), a slightly lower number of SC (38–47 vs. 45–59), a higher number of SL (usually 6 vs. 5), and the presence of an orange V-shaped zone behind a black collar (vs. absent).

Rhabdophis angeli is distinguished from R. hmongorum (distributed in Northern Vietnam, Northern Laos, and Yunnan Province, China) by having a lower number of DSR (15 vs. 17), a lower number of VEN (118–127 vs. 136– 151), a slightly lower number of SC (38–47 vs. 43–59), a lower number of TEM (usually 1+1 vs. 1+2), a slightly lower number of MT (20–23 vs. 25), the presence of an orange V-shaped zone behind the black collar (vs. absent), and the presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Rhabdophis angeli is distinguished from R. kaiyuanensis (distributed in Yunnan Province, China, and possibly in Northern Vietnam) by having a lower number of VEN (118–127 vs. 147–153), a slightly lower number of SC (38– 47 vs. 44–58), a lower number of TEM (usually 1+1 vs. 1+2), the presence of an orange V-shaped zone behind the black collar (vs. absent), the presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Rhabdophis angeli is distinguished from R. leonardi (distributed in Myanmar [Kachin State], China [Yunnan and Sichuan provinces, Xizang AR], and India [ Nagaland and Arunachal Pradesh states]) by having a lower number of DSR (15 vs. 17), a lower number of VEN (118–127 vs. 151–157), a slightly lower number of SC (38–47 vs. 44–64), a slightly higher number of MT (20–23 vs. 19), the presence of an orange V-shaped zone behind the black collar (vs. absent), and the presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Rhabdophis angeli is distinguished from R. nuchalis (including the provinces of Hubei, Hunan, Shaanxi, Gansu, and Sichuan, as well as Chongqing Municipality) by having a lower number of VEN (118–127 vs. 144–169), a lower number of TEM (usually 1+1 vs. 1+2), a top of head grey (vs. olive); a presence of an orange V-shaped zone behind the black collar (vs. absent), lips with two conspicuous black oblique bands (vs. absent), ventral surface of head and neck that is cream with black spots, a posteriorly gradually becoming entirely black (vs. uniform black, or black in the middle and olive on the sides), and a presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Rhabdophis angeli is distinguished from R. pentasupralabialis (distributed in Yunnan and Sichuan provinces, China) by having a lower number of VEN (118–127 vs. 144–169), a higher number of IL (7 or 8 vs. 6), a higher number of MT (20–23 vs. 18), the top of the head dark grey (vs. olive), the presence of an orange V-shaped zone behind the black collar (vs. absent), lips with two conspicuous black oblique bands (vs. absent), and the presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Lastly, Rhabdophis angeli is distinguished from R. swinhonis (endemic to Taiwan Island, China) by having a lower number of TEM (usually 1+1 vs. 1+2), the top of the head, occiput and nape before the black collar being grey (vs. reddish-brown); an orange V-shaped zone behind the black collar [vs. a reddish-brown zone ( i. e., occiput and nape reddish) before the black collar]; the ventral surface of the head and neck being cream with black spots, posteriorly gradually becoming entirely black (vs. yellowish-brown, powdered with brown on the sides); and the presence of two faint dorsolateral black cross-bars alongside the body (vs. absent).

Distribution and natural history notes ( Fig. 5 View FIGURE 5 ). Rhabdophis angeli is currently known from Tam Dao NP, Phu Tho Province, Vietnam, as well as from several localities in Guangdong Province, China, including Aizhai Village (Renhua County), Mt. Wutong (Shenzhen City), Mt. Nankun (Huizhou City), Mt. Yinping (Dongguan City), and Mt. Tianjing (Shaoguan City). Given the species geographic range, it is likely that R. angeli also occurs in Guangxi Province, China, and possibly in other provinces of northeastern Vietnam. This species is terrestrial and primarily diurnal. It preys predominantly on earthworms and inhabits lowland evergreen forests and submontane forests at elevations ranging from 56 to 900 m asl ( Zhu et al. 2014; present study).

Conservation status. Currently, Rhabdophis angeli , as well as Rhabdophis guangdongensis syn. nov., are assessed as Data Deficient (DD) under the IUCN Red List categories ( Stuart & Nguyen 2012; Qi et al. 2024). Rhabdophis angeli is reliably known from seven localities across Phu Tho Province, Vietnam, and Guangdong Province, China, including one national park. Although the species appears relatively widespread geographically, it remains rare throughout its known range, possibly due to a highly secretive way of life in humid areas. Notably, extensive field surveys conducted by T.V. Nguyen in 2022, 2023, and 2024 at Tam Dao NP failed to yield any additional specimens. The principal threat to this species is habitat loss and degradation, particularly in Tam Dao NP, where habitat destruction and large-scale tourism infrastructure development are ongoing and intensively (T.V. Nguyen pers. obs.). Although critical aspects of the species biology, including its full distributional extent, population dynamics, reproductive behaviour, ecology, and toxicology, remain poorly understood, we suggest that Rhabdophis angeli be classified as Near Threatened (NT) according to the criteria of the IUCN Red List (IUCN 2024). This recommendation is based on its occurrence in scattered localities in its relatively wide range, the current absence of evidence indicating rapid population declines but potential threats by destruction of its habitat.