Lycodon poyarkovi, Nguyen & Vogel, 2025

Lycodon poyarkovi sp. nov.

( Tables 1–2 View TABLE 1 View TABLE 2 ; Figs. 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 , 8–9 View FIGURE 8 View FIGURE 9 ; Appendix III)

Chresonymy:

Lycodon paucifasciatus View in CoL (non Lycodon paucifasciatus Rendahl View in CoL in Smith, 1943)— Orlov et al. (2003: 217–240: in part); Ziegler et al. (2004: 34, in part); Nguyen et al. (2009: 320, in part); Vogel et al. (2009: 131–182, in part); Luu et al. (2013: 297, in part); Poyarkov et al. (2023: 343, in part); Uetz et al. (2024, page “ Lycodon paucifasciatus View in CoL ”, in part).

Dinodon rosozonatum View in CoL (non Dinodon rosozonatum Hu & Zhao, 1966 View in CoL )— Luo et al. 2010: 579–582, in part).

Lycodon cf. rosozonatum View in CoL — Pham et al. (2019: 166)

Dinodon rufozonatum (non Lycodon rufo-zonatus Cantor, 1842 View in CoL )— Ziegler et al. (2004: 34, in part); Nguyen et al. (2009: 320, in part); Luu et al. (2013: 97, in part).

Diagnosis. A new species of the genus Lycodon , characterized by: size medium-large, maximum total length up to 817 mm; loreal usually not in contact with eye; dorsal scale rows 19–17(rarely 19)–15; 5–7 dorsal scale rows keeled at midbody; 221–228 ventrals; 83–92 subcaudals, paired; 8 supralabials with numbers 3–5 touching the eye; 1 preocular, 2 postoculars; temporals 2+3; anal plate undivided; dorsal crossbands narrow, with pinkish orange color, 24–33 crossbands on dorsum, 11–14 crossbands on tail, first crossband starting at VEN 10–15; head black, the plates conspicuously margined with pinkish-orange; venter reddish orange or cream; upper maxillary teeth: 6+3–4+2.

Holotype: ZFMK 80661 About ZFMK (adult female) collected in Phong Nha-Ke Bang National Park , Minh Hoa District, Quang Binh Province, Vietnam ( Fig. 4 View FIGURE 4 ).

Paratypes (n=3): DTU 616 (adult female) collected in Dong Chau-Khe Nuoc Trong NR, Kim Thuy Commune , Le Thuy District, Quang Binh Province, Vietnam (16.976815°N, 106.639777°E; elevation 200 m a.s.l.) by T.Q. Phan on 01 May 2023 GoogleMaps ; ZFMK 80662 About ZFMK (adult male; Fig. 5 View FIGURE 5 ) and ZFMK 86452 About ZFMK (adult female) collected in Phong Nha-Ke Bang NP , Quang Binh Province, Vietnam .

Description of the holotype ( Fig. 4 View FIGURE 4 ). Body robust, slightly compressed laterally; tail comparatively long, thin and tapering; head elongate, longer than wide, flattened moderately distinct from the neck; snout elongate, flattened, projecting over the lower jaw; nostrils rather large, in dorsal-lateral position, round in shape; eye rather large with vertical pupil.

Body size. SVL: 660 mm, TaL: 157 mm, TL 817 mm, ratio TaL/TL: 0.192.

Body scalation. Dorsal scale rows 19–17–15, the 7 upper rows feebly keeled at midbody; scales of the vertebral row slight enlarged; no apical pits; 228 ventrals; 88 subcaudals, all paired; anal plate undivided.

Head scalation. Rostral heptagonal, wider than high, slightly visible from above; nasal single, elongated; nasal surrounded by the first two supralabials, rostral, internasal, and prefrontal; internasals two, curved, slightly wider than long, in contact with rostral anteriorly, nasal, and prefrontal; two prefrontals, large, subrectangular, prefrontal slightly shorter than frontal; prefrontals in contact with internasals, nasals, preoculars, and frontal; frontal rather small, pentagonal, tapering posteriorly, shorter than the distance from tip of snout to frontal; parietals longer than wide, in contact on approximately the length of frontal; 1/1 supraocular, distinctly wider than long, in contact with prefrontal; 1/1 loreal, contacting eye; 1/1 preocular, large, higher than wide, in broad contact with prefrontal; subocular absent; 2/2 postoculars; 2+3 temporals on both sides; 8/8 supralabials, first and second in contact with nasal, second and third in contact with loreal, third to fifth in contact with eye, seventh largest; infralabials 10/10, first pair in broad contact with each other, first to fifth in contact with anterior pair of chin shields; posterior chin shields equal to anterior ones in lenght, separated from each other by a pair of small scales.

Colouration in preservative: Dorsum blackish-brown with 33 light transversal cross bands on body and 14 on tail. Head black with distinct inverted V on the nape. Venter cream and getting distinctly darker towards the cloaca; ventral surface of tail blackish.

Variation (see Tables 1–2 View TABLE 1 View TABLE 2 and Figs. 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 for the details).The longest known specimen is 825+ mm long (paratype, female; SVL 675 mm, TaL 150+ mm; DTU 616 ). The longest known male is 673 mm long ( SVL 536 mm, TaL 137 mm; ZFMK 80662 About ZFMK ); ratio TaL/TL: 0.19–0.20 (male: 0.20; females: 0.19).

Body scalation. 19–17(rarely 19)–15 DSR; 221–228 VEN, without sexual dimorphism; 83–92 SC (92 in male; 83–88 in females).

Head scalation. SL 8, IL 10; loreal rarely touching the orbit.

Dentition (based ZFMK 80662 [paratype] and ZFMK 86452 [paratype]). Upper maxillary tooth formula: 6 anterior teeth, the last two much enlarged + a wide gap + 3–4 short teeth + a small gap, shorter than posterior teeth + two much enlarged teeth.

Main characters of pattern. In life, the dorsum is blackish with 24–33 pinkish orange narrow crossbands on the body and 11–14 narrow crossbands on the tail. First light crossband starting between ventral scale 10–15, its length 7.0–11.5 ventral scales long at base, and 2.0–2.5 vertebral dorsal scales long. On the neck an inverted V shaped pink marking present. Venter cream or light beige-brown, uniform on the anterior quarter or third of the body, then getting progressively more intensely speckled with dark brown posteriorly; posterior part of the venter entirely obscured with dark brown; tail either entirely dark brown below or with irregular blotches corresponding to light crossbands ( Figs. 4–6 View FIGURE 4 View FIGURE 5 View FIGURE 6 ).

Hemipenis (in situ). According to Vogel et al. 2009, the hemipenis description is based on specimen ZFMK 80662 (paratype). The organ is single, not forked, short, and massive. It reaches SC 7 or 9. It is densely covered with numerous spines on the distal 2/3, smooth and folded on its base and the first third. Proximal spines are much larger and wider than distal spines, decreasing progressively to become short but very dense on the distal half. The sulcus lips are very prominent and well developed throughout, densely covered with short spines on their outer side.

Comparisons: Morphologically, Lycodon poyarkovi sp. nov. is most closely resembles L. anakradaya , L. cardamomensis , L. paucifasciatus , L. rosozonatus , and L. gibsonae , because of the following characteristics: medium to large body (TL≥ 600 mm); dorsal scales smooth or weakly keeled at midbody; 17–19 scales at midbody; body with red or pinkish crossbands on black or brown background; a pale inverted V on the nape (see Figs. 1 View FIGURE 1 , 2 View FIGURE 2 , 7 View FIGURE 7 ). Therefore, morphological comparisons with these five species appear to be the most pertinent. The main diagnostic characters separating Lycodon poyarkovi sp. nov. from these five species are summarized in Table 2 View TABLE 2 and Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 , 7 View FIGURE 7 .

Lycodon poyarkovi sp. nov. differs from L. anakradaya (inhabiting Southern Vietnam) by having: (1) slightly lower number of VEN in females (221–228 [avg. 223.33] vs. 232); (2) slightly lower number of SC in females (83–88 [avg. 85.50] vs. 91); (3) higher number of BB in both sexes (24 in male, 25–33 [avg. 27.67] in females vs. 13 in male, 12 in female; (4) higher number of TB in both sexes (11 in male, 11–14 [avg. 12.50] in females vs. 7 in male, 5 in female).

Lycodon poyarkovi sp. nov. differs from L. cardamomensis (inhabiting Southwest Cambodia and Southeastern Thailand) by having: (1) slightly lower number of SC in females (83–88 [avg. 85.50] vs. 91–92 [avg. 91.50]); (2) higher number of BB in both sexes (24 in male, 25–33 [avg. 27.67] in females vs. 12–13 [avg. 12.33] in males, 13–14 [avg. 13.50] in females); (3) higher number of TB in both sexes (11 in male, 11–14 [avg. 12.50] in females vs. 6 in both sexes); (4) lower number of FB in male (15 vs. 20); (5) lower number of BV in males (2 vs. 5).

Lycodon poyarkovi sp. nov. differs from L. rosozonatus (endemic to Hainan Island , China) by having: (1) usually lower number of MSR in both sexes (17 [rarely 19] vs. 19); (2) slightly lower number of BB in males (24 vs. 27–35 [avg. 31.20]); (3) higher number of FB in males (15 vs. 8–12 [avg. 10.80]); (4) slightly higher number of BaB in males (11 vs. 5–10 [avg. 7.80]).

Lycodon poyarkovi sp. nov. further differs from L. gibsonae (inhabiting Khorat Plateau, Thailand) by having: (1) higher number of BB in males (24 vs. 17–18 [avg. 17.33]; (2) higher number of TB in males (11 vs. 8–9 [avg. 8.67]); (3) lower number of BV in males (2 vs. 4.5–6 [avg. 5.00]); (4) lower max SVL in males (536 mm vs. 906 mm).

In particular, Lycodon poyarkovi sp. nov. is distinguished from L. paucifasciatus by having: (1) higher number of VEN in males (221 vs. 203–219 [avg. 213.00]); (2) higher number of SC in females (83–88 [avg. 85.50] vs. 92); (3) higher number of BB in both sexes (24 in male, 25–33 [avg. 27.67] in females vs. 10–17 [avg. 13.60] in males, 10–11 [avg. 10.50] in females); (4) higher number of TB in both sexes (11 in male, 11–14 [avg. 12.50] in females vs. 5–8 [avg. 6.80] in males, 5 in females); (5) lower number of FB in both sexes (15 in male, 10–13 [avg. 11.00] in females vs. 17–24 [avg. 19.20] in males, 19 in females); (6) slightly higher number of BaB in males (11 vs. 5–10 [avg. 7.80]) but in contrast of females (7–9.5 [avg. 8.17] vs. 11–14 [avg. 12.50]); (7) lower number of BV in both sexes [2 in male, 2–2.5 [avg. 2.17] in females vs. 3–3.5 [avg. 3.20] in males, 4–5 [avg. 4.50] in females).

Lastly, Lycodon poyarkovi sp. nov. was previously misidentified with L. rufozonatus or Dinodon cf. rufozonatum (see Ziegler et al. 2004; Nguyen et al. 2009). The new species can be distinguished from L. rufozonatus (data from Nguyen et al. in preparation) by having: (1) higher number of VEN in both sexes (221 in male, 221–228 [avg. 223.33] in females vs. 198–216 [avg. 204.45] in males, 198–214 [avg. 199.75] in females); (2) higher number of SC in both sexes (92 in male, 83–88 [avg. 85.50] in females vs. 62–83 [avg. 74.78] in males, 60–81 [avg. 68.67] in females); (3) lower number of BB in both sexes (24 in male, 25–33 [avg. 27.67] in females vs. 45–78 [avg. 65.73] in males, 50–65 [avg. 58.50] in females); (4) lower number of TB in males (11 vs. 19–28 [avg. 22.20]); (5) dorsal crossbands pinkish (vs. rose red or grey).

Etymology: We name the new species in honour of Dr. Nikolay A. Poyarkov, an Assistant Professor at the Lomonosov Moscow State University (Moscow, Russia), in recognition of his contribution to the herpetology, especially on the Indo-Burma region including Vietnam. Futhermore, he was the first to note the distinction between the new species and the Lycodon paucifasciatus species complex group. We suggest the following common names for the new species: “Poyarkov’s Big-tooth Snake” (in English) and “ Rắn khuyết Trường SƠn ” (in Vietnamese).

Natural history notes: The new species L. poyarkovi sp. nov. has a narrow distribution, seems to be quite uncommon due low encounter rates, is a nocturnal snake, usually observed crawling on the ground but also climbing quite well. It is observed in small puddles, edges of small and medium streams inhabiting montane forests at ca. 300–800 m asl. In Phong Nha-Ke Bang NP, the one individual (uncollected, see Fig. 6H View FIGURE 6 ) was observed at night on the ground in a forest clearing or crawling through the roots of a fallen tree, lying at the edge of a small creek (see Fig. 8A View FIGURE 8 ). Colubrid species recorded in sympatry with the new species in Phong Nha-Ke Bang NP included: Ahaetulla prasina (Boie) , Chrysopelea ornata (Shaw) , Boiga bourreti Tillack, Ziegler & Le , B. guangxiensis Wen , B. multomaculata (Boie) , B. cf. kraepelini Stejneger , Coelognathus radiatus (Boie) , Dendrelaphis ngansonensis (Bourret) , Elaphe taeniura (Cope) , Lycodon davisonii , L. cf. fasciatus , L. futsingensis , L. ruhstrati abditus , Liopeltis pallidonuchalis Poyarkov, Nguyen & Vogel , Oligodon chinensis (Günther) , O. cinereus (Günther) , Oreocryptophis porphyraceus (Cantor) , Ptyas multicincta (Roux) , P. korros (Schlegel) , P. mucosa (Linnaeus) , Gonyosoma boulengeri (Mocquard) , and G. coeruleum Liu, Hou, Lwin, Wang & Rao ( Ziegler et al. 2004; Luu et al. 2013; Poyarkov et al. 2019; our data). In Dong Chau-Khe Nuoc Trong NR, the specimen DTU 616 was found while crawling on a dry tree branch near a stream about 1.5 m above the ground (see Fig. 8B View FIGURE 8 ). Colubrid species recorded sympatry with the new species in Dong Chau-Khe Nuoc Trong NR included: Ahaetula prasina , Chrysopelea ornata , Boiga guangxiensis , B. cf. kraepelini , Dendrelaphis cf. pictus (Gmelin) , Ptyas multicincta , Lycodon laoensis , L. futsingensis , L. ruhstrati abditus , Oligodon chinensis , Oreocryptophis porphyraceus , and Gonyosoma boulengeri ( Pham et al. 2019; our data). The diet of the new species is not known, though it likely consists of frogs and snakes ( Vogel et al. 2009; our data).

Distribution ( Fig. 9 View FIGURE 9 ). The new species is to date known only from two localities in Quang Binh Province, Vietnam, namely: Phong Nha-Ke Bang NP in Minh Hoa District and Dong Chau-Ke Nuoc Trong NR in Le Thuy District, within the northern part of the Truong Son Mountain Range, which is isolated from the adjacent mountain massifs by lowland areas and is characterized by a high level of herpetofaunal endemism ( Poyarkov et al. 2021, 2023). The new species is likely an endemic of this mountain region; further records from other mountain areas in the Bac Huong Hoa NR, Quang Tri Province of Vietnam (see discussion) as well as Khammouan Province of Central Laos are anticipated.