Lycodon calcarophilus, Vogel & Bragin & Poyarkov & Nguyen, 2025

Lycodon calcarophilus sp. nov.

urn:lsid:zoobank.org:act:7332FEAD-1D55-47B1-AE42-D4E78AAD76E9

( Figures 2–5 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , Figure S1 View FIGURE 1 ; Tables 1–3, Appendix Table S1, S5)

Chresonymy:

Lycodon fasciatus View in CoL (nec Ophites fasciatus Anderson, 1879 View in CoL ) — Ziegler et al. (2004: 34, in part); Ziegler et al. (2006: 16, in part); Ziegler et al. (2007: 18, in part); Vogel et al. (2009: 179, in part); Nguyen et al. (2009: 319, in part); Luu et al. (2013: 13, in part).

Lycodon (Lycodon) fasciatus View in CoL — Poyarkov et al. (2023: 341, in part).

Lycodon fasciatus View in CoL clade 2 — Nguyen et al. (2025: 5, 7, 36).

Holotype. ZMMU Re-18273 (adult female; field ID NAP –13929) from Thuong Hoa Commune , Minh Hoa District, Quang Binh Province, Vietnam (17.716°N, 106.003°E; elevation ca. 250 m asl.) collected by N.A. Poyarkov and A.M. Bragin on 04 August 2022. GoogleMaps

Paratypes (n = 3). ZFMK 86448–50 About ZFMK (three adult females) from Cha Noi Valley within Phong Nha-Ke Bang NP, Xuan Trach Commune, Bo Trach District, Quang Binh Province, Vietnam collected by R. Hendrix and T. Ziegler on 15 July 2006 .

Additional material (n = 2). ZFMK 80665 About ZFMK (juvenile, sex unknown) collected in Phong Nha-Ke Bang NP, Minh Hoa District , Quang Binh Province, Vietnam; see detail in Ziegler et al. (2004: 34); SIFASV 110 (subadult male, released) from Son Trach Commune , Bo Trach District, near Phong Nha-Ke Bang NP, Quang Binh Province, Vietnam (ca. 17.601°N, 106.273°E; elevation 200 m asl), observed by P.L. Tran and GoogleMaps T. V. Nguyen on 5 March 2024 .

Diagnosis. A small-sized species of Lycodon from central Vietnam with a maximum snout-vent length of 505 mm, relative tail length 0.19–0.22, dorsal scale rows 17–17–15, 5–7 upper dorsal scale rows keeled at midbody, ventrals 214–219, subcaudals 83–88, paired, and cloacal plate undivided, supralabials usually eight with third to fifth scales in contact with eye, infralabials ten (rarely nine), the first five in contact with anterior chin shields, preocular 1/1, blocking prefrontals from contacting eye, loreal in narrow contact with eye, postoculars 2/2, temporals 2+3 (rarely 2+2). Dorsum black in life with 19–25 white or slight brownish-grey light body cross-bands and 10–15 tail cross-bands; first light cross-band starting between ventrals 12–15, 10–13 ventral scales long at base and 4–5 vertebral dorsal scales long; in life, head slight dark brown in adults, white spots present across most supralabials, underside of head white, scale sutures of chin and throat with dark brown mottling; venter with discrete light and dark cross-bands, absent small irregular spots prevalent posteriorly.

Description of holotype ( Fig. 2 View FIGURE 2 , Appendix Fig. S1 View FIGURE 1 ). Specimen ZMMU Re- 18273 in excellent condition, small ventral incision at midbody. Body elongated, laterally compressed. Tail comparatively long, thin and tapering ( Fig. 2A View FIGURE 2 ). Head ovate in dorsal profile, flattened moderately distinct from neck ( Fig. 2B View FIGURE 2 ); temporal and parietal regions slightly raised in lateral profile; snout elongate, depressed downwards, upper jaw projecting further than lower jaw, no distinct canthus rostralis ( Fig. 2B–C View FIGURE 2 ). Nostrils are round, circular, and positioned medially within nasal. Eyes moderate relative to head; pupil elliptical, vertical ( Fig. 2B View FIGURE 2 ).

Measurements. SVL 505 mm, TaL 120 mm, TL 625 mm, TaL/TL ratio 0.19, head length measured from tip of the snout to the jaw angle 14.2 mm, head length measured from tip of the snout to the posterior edge of parietals 11.4 mm, maximal head width 8.3 mm, length of the eyeball 1.8 mm, eye-narial distance measured as the distance from the anteriormost edge of the eyeball and the posterior edge of the naris 2.9 mm, eye-snout distance measured as the distance from the anteriormost edge of the eyeball and the snout 4.3 mm.

Body scalation. Dorsal scales arranged in 17–17–15 rows; all dorsal scales smooth anteriorly, keeled at midbody and posteriorly except for the first five outermost rows on either side at midbody and the two outermost rows posteriorly, which are smooth; vertebral row of dorsal scales not enlarged; apical pits absent. Ventral scales 217, laterally angulated, forming a slight keel; subcaudals 83, paired, laterally angulated; total body scales 301; subcaudal ratio 0.28; cloacal plate undivided.

Head scalation. Rostral heptagonal, wider than high, barely visible from above; nasal single, elongated, pierced by the nostril; 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 the frontal; 1/1 supraocular, distinctly wider than long, in contact with prefrontal; 1/1 loreal, contacting eye; 1/1 preocular, vertical and subrectangular, in broad contact with prefrontal; presubocular and subocular scales absent; 2/2 postoculars, vertical and subrectangular, bottommost scale slightly larger; 2+3 temporals on both sides, lowermost anterior temporal largest; 8/8 supralabials, first and second in contact with nasal, second and third in contact with loreal, third to fifth in contact with eye, sixth largest; 10/10 infralabials, first pair in broad contact with each other, first to fifth in contact with anterior pair of chin shields; posterior chin shields roughly the same length as anterior shields; 4/4 gular scales (excluding two preventrals) behind posterior row of chin shields.

Colour of holotype in life: Dorsal surface of the body and tail dark blackish brown, with 21 distinct pale pinkish cream cross-bands on the body and 12 on the tail ( Fig. 2A View FIGURE 2 ). Each cross-band is approximately five dorsal scales wide in the anterior body (first five cross-bands), becoming narrower posteriorly. Light cross-bands are pale pinkish-cream with irregular brownish-grey speckling, particularly expanded at ventrolateral margins. The first dorsal cross-band starts at the level of the 13th ventral scale, extending across approximately 12 ventrals and five dorsal vertebral scales (Appendix Fig. S1 View FIGURE 1 ). Head uniformly blackish-brown dorsally and laterally ( Fig. 2B–C View FIGURE 2 ); throat cream-colored, with a diffuse dark blotch on the preventral and first ventral scale ( Fig. 2D View FIGURE 2 ). Venter dark grey to black with alternating faint cream-coloured, cross-bands, more regular and distinct in the anterior body; dark ventral bands span 7–10 ventrals, light bands 6–10 ventrals. Posteriorly, ventral cross-bands become irregular; some ventrals are bicolored, dark brownish black on one side and cream on the other. The underside of the tail exhibits a pattern similar to the posterior venter.

Colour of holotype in preservation: After more than three years in preservation, the coloration of the specimen has remained largely unchanged (Appendix Fig. S1 View FIGURE 1 ). The dorsal ground color and the pattern of pale bands are still distinct, although the overall contrast has slightly faded. The dorsal surfaces retain a dark brown to blackish tone with alternating irregular pale crossbands, while the ventral surfaces appear creamy white with brown blotches that remain clearly visible. The head pattern, including the postocular stripe and labial markings, also remains well defined. These observations suggest a high degree of color stability in preservative for this species.

Variations (see Table 1 and Figs: 3–5). All examined specimens are morphologically consistent with the holotype in general appearance and scalation, but exhibit minor variation in the following features: total length in females ranges up to 625 mm, while the maximum size of males remains unknown; ratio TaL/TL: 0.19–0.22 (male: 0.21; females: 0.19–0.22).

Body scalation. 17–17–15 DSR; 214–219 VEN, without sexual dimorphism; 83–88 SC, without sexual dimorphism.

Head scalation. SL 8 (third to fifth in contact with eye), IL 10 (rarely 9 in 1/ 6 specimens); loreal touching the eye; PrO 1/1; PtO 2/2; temporals 2+3, rarely 2+2 (1/ 6 specimens).

Main characters of the pattern. Dorsum dark blackish brown with 19–25 pale cross-bands on the body and 10–15 on the tail. Cross-bands whitish with fine brown speckling, more prominent at ventrolateral margins; anterior body cross-bands approximately 4–5 dorsal scale rows wide along the vertebral line. The first body cross-band begins at the level of ventral scale 12–15. Head colouration is variable. Dorsally, the head is uniformly dark brown to black in most adults; juveniles and subadults often exhibit paler temporal regions and diffuse lighter pigmentation along the loreal area and supralabials. Lateral surfaces of the head range from strongly contrasting dark and cream tones to more subtly blended margins. Ventrolateral margin of head and throat cream-coloured, sometimes with small brown blotches extending onto preventral scales. Venter dark brown with faint, cream-coloured, transverse bands, more regular in the anterior body. In the posterior body, ventral cross-bands are irregular; some ventral scales are bicolored, with one half dark and the other cream.

Etymology. The specific epithet calcarophilus is an adjective in the nominative singular, modified to match the masculine gender of the genus name. It is derived from the Latin calcar, meaning “limestone”, and -philus, meaning “loving” or “having an affinity for”. The name refers to the species’ apparent preference for limestone habitats. We suggest the following common names in English: “Limestone Wolf Snake”, in Vietnamese: “Rắn khuyết Việt Nam”, and in the Russian language: “Karstovyi volkozub” (Карстовый волкоЗУб).

Comparisons. Lycodon calcarophilus sp. nov. is assigned to the Lycodon fasciatus group (e.g., Wostl et al. 2017; Janssen et al. 2019; Wang et al. 2021; Nguyen et al. 2024a; Vogel et al. 2024; Nguyen et al. 2025) based on its phylogenetic position (see Fig. 1 View FIGURE 1 ) and is overall most similar to other species comparable to these 16 species that appear to be the most pertinent. The main diagnostic characters separating Lycodon calcarophilus sp. nov. from these 16 species are summarised in Tables 2–3.

ruhstrati . Characters highlighted in bold are considered diagnostic (with respect to Lycodon calcarophilus sp. nov.)

Lycodon calcarophilus sp. nov. differs from L. butleri by having: smaller maximum SVL (500 mm vs. 648 mm), lower number of BB (19–25 vs. 28–37), slight lower number of TB (10–15 vs. 14–25); it differs from L. davidi by having: larger maximum SVL (500 mm vs. 308 mm), lower number of VEN (214–219 vs. 224), lower number of SC (83–88 vs. 99), lower number of BB (19–25 vs. 84), lower number of TB (10–15 vs. 38), loreal touching the eye (vs. not touching), black dorsal ground color (vs. dark brown); it differs from L. cavernicolus by having: larger maximum SVL (500 mm vs. 406 mm), lower number of VEN (214–219 vs. 232–245), lower number of SC (83–88 vs. 92–113), lower number of BB (19–25 vs. 36–45), lower number of TB (10–15 vs. 29–41), black dorsal ground color (vs. light brown), banded ventral pattern (vs. plain); it differs from L. gammiei by having: smaller maximum SVL (500 mm vs. 1110 mm), lower number of SC (83–88 vs. 101–112), lower number of BB (19–25 vs. 42–58), lower number of TB (10–15 vs. 16–23), loreal touching the eye (vs. not touching), white anteriorly, slight brownish grey posteriorly cross-bands (vs. yellow to olive-yellow); it differs from L. gongshan by having: smaller maximum SVL (500 mm vs. 798 mm), lower number of BB (19–25 vs. 26–46); it differs from L. latifasciatus by having: smaller maximum SVL (500 mm vs. 680 mm), slight higher number of VEN (214–219 vs. 206–216), lower number of SC (83–88 vs. 90–96), lower number of BB (19–25 vs. 29–36), lower number of TB (10–15 vs. 29–41), white anteriorly, slight brownish grey posteriorly cross-bands (vs. orange or light brown); it differs from L. liuchengchaoi by having: smaller maximum SVL (500 mm vs. 676 mm), higher number of SC (83–88 vs. 68–81), white anteriorly, slight brownish grey posteriorly cross-bands (vs. cream anteriorly, yellow, orange or light brown posteriorly); it differs from L. multifasciatus by having: smaller maximum SVL (500 mm vs. 570 mm), lower ratio TaL/TL (0.19–0.22 vs. 0.23–0.26), lower number of VEN (214–219 vs. 227–237), lower number of SC (83–88 vs. 106–117), lower number of BB (19–25 vs. 51–72), lower number of TB (10–15 vs. 25–35), loreal touching the eye (vs. not touching), black dorsal ground color (vs. dark brown), white anteriorly, slight brownish grey posteriorly cross-bands (vs. light brown), banded ventral pattern (vs. plain); it differs from L. multizonatus by having: higher ratio TaL/TL (0.19–0.22 vs. 0.16–0.18), higher number of VEN (214–219 vs. 191–202), higher number of SC (83– 88 vs. 56–75), lower number of BB (19–25 vs. 55–62), cloacal plate undivided (vs. divided), white anteriorly, slight brownish grey posteriorly cross-bands (vs. orange or reddish brown); it differs from L. obvelatus by having: larger maximum SVL (500 mm vs. 447 mm), higher number of VEN (214–219 vs. 199), higher number of SC (83–88 vs. 76), lower number of BB (19–25 vs. 31), dorsal scales keeled (vs. smooth), white anteriorly, slight brownish grey posteriorly cross-bands (vs. light orange or salmon); it differs from L. pictus by having: smaller maximum SVL (500 mm vs. 543 mm), dorsal scales keeled (vs. smooth); it differs from L. serratus by having: lower ratio TaL/TL (0.19–0.22 vs. 0.24), higher number of VEN (214–219 vs. 198), slight lower number of BB (19–25 vs. 26), lower number of TB (10–15 vs. 29–41), dorsal scales keeled (vs. smooth), cloacal plate undivided (vs. divided), black dorsal ground color (vs. dark brown), white anteriorly, slight brownish grey posteriorly cross-bands (vs. olive brown (tawny olive)); it differs from L. sidiki by having: smaller maximum SVL (500 mm vs. 650 mm), higher number of VEN (214–219 vs. 195–212), lower number of SC (83–88 vs. 92–113), slight lower number of BB (19–25 vs. 25–33), white anteriorly, slight brownish grey posteriorly cross-bands (vs. light grey); it differs from L. synaptor by having: larger maximum SVL (500 mm vs. 395 mm), higher number of VEN (214–219 vs. 201–203), higher number of SC (83–88 vs. 68–69), lower number of BB (19–25 vs. 30–31), higher number of TB (10–15 vs. 9), loreal touching the eye (vs. not touching); it differs from L. yunnanensis by having: smaller maximum SVL (500 mm vs. 550 mm), higher number of VEN (214–219 vs. 186–202), higher number of SC (83–88 vs. 67–80).

Lastly, Lycodon calcarophilus sp. nov. most closely resembles L. fasciatus and L. ruhstrati . The main diagnostic characters separating Lycodon calcarophilus sp. nov. from these two species are summarised in Table 2 and illustrated in Appendix Figs. S2 View FIGURE 2 . Lycodon calcarophilus sp. nov. differs from L. fasciatus by having: higher number of VEN (214–219 [avg. 216.7] vs. 197–213 [avg. 206.1], higher number of TOTAL (300–307 [avg. 303.0] vs. 278–302 [avg. 288.9]), lower number of BB (19–25 [avg. 21.5] vs. 28–43 [avg. 32.3]), higher number of BV (4.0–5.0 [avg. 4.7] vs. 1.0–3.5 [avg. 2.3], white anteriorly, slight brownish grey posteriorly cross-bands (vs. variable, light, reddish or orange brown anteriorly and posteriorly), banded ventral pattern, absent spots posteriorly (vs. banded, spots usually present posteriorly); It further differs from the sympatric Lycodon ruhstrati abditus by having: lower number of SC (83–88 [avg. 85.3] vs. 90–115 [avg. 97.1]), lower number of TOTAL (300–307 [avg. 303.0] vs. 305–342 [avg. 319.8]), lower subcaudal ratio SCR (0.28–0.29 [avg. 0.28] vs. 0.28–0.34 [avg. 0.30]), lower number of BB (19–25 [avg. 21.5] vs. 17–47 [avg. 32.9]), loreal touching the eye (vs. not touching), black dorsal ground color (vs. dark brown), banded ventral pattern, absent spots posteriorly (vs. plain & spotted); it differs from L. ruhstrati ruhstrati (Fischer) by having: slight lower ratio TaL/TL (0.19–0.22 [avg. avg. 0.21] vs. 0.21–0.25 [avg. 0.23]), lower number of SC (83–88 [avg. avg. 85.3] vs. 99–114 [avg. 105.3]), lower number of TOTAL (300–307 [avg. 303.0] vs. 321– 335 [avg. 326.4], lower subcaudal ratio SCR 0.28–0.29 [avg. 0.28] vs. 0.31–0.34 [avg. 0.32]), lower number of BB (19–25 [avg. 21.5] vs. 29–46 [avg. 38.0]), higher number of BV (4.0–5.0 [avg. 4.7] vs. 2.0–2.5 [avg. 2.1]), loreal touching the eye (vs. not touching), banded ventral pattern, absent spots posteriorly (vs. plain & spotted).

Distribution and Natural history notes ( Figs. 6–7 View FIGURE 6 View FIGURE 7 ). Lycodon calcarophilus sp. nov. is currently known only from Phong Nha-Ke Bang NP, located in the northern part of the Northern Annamites (Truong Son Mountains). This massif is geographically isolated from adjacent mountain systems by intervening lowland areas and is recognised as a centre of herpetofaunal endemism ( Poyarkov et al. 2021, 2023). The new species is likely endemic to this region, although additional populations may occur in nearby limestone karst formations, including Dong Chau-Ke Nuoc Trong NR in Quang Binh Province, Bac Huong Hoa NR in Quang Tri Province, and in adjacent Khammouan Province of central Laos. The type series was collected in a multi-layered monsoon evergreen forest with primary elements, located in a lowland area between karst outcrops at 200–250 m asl, on gentle slopes with loamy soils mixed with limestone and schist, and a well-developed leaf litter layer. The upper canopy (25–30 m tall) was dominated by Pommetia pinnata (Sol. ex G.Forst.) Merr. ( Sapindaceae ), with admixtures of Magnolia sp. ( Magnoliaceae ), Dipterocarpus kerrii King ( Dipterocarpaceae ), Burretiodendron sp. ( Malvaceae ), cf. Canarium L. ( Burseraceae ), Dacryodes sp. ( Burseraceae ), Endospermum sinensis Benth. ( Euphorbiaceae ), Artocarpus sp. J .R.Forst. & G.Forst. ( Moraceae ), Ficus sp. L. ( Moraceae ), Litsea sp. Lam. ( Lauraceae ), cf. Chisocheton Blume , Dysoxylum Blume , cf. Aglaia Lour. , Amoora sp. Roxb. ( Meliaceae ), Madhuca sp. Gmel. ( Sapotaceae ), Elaeocarpus spp. L. ( Elaeocarpaceae ), Mangifera sp. L. ( Anacardiaceae ), Lithocarpus sp. Blume ( Fagaceae ), and Tetrameles nudiflora R.Br. ( Tetramelaceae ). The undergrowth and shrub layers were well-developed, with a high diversity of lianas and epiphytes ( Phan & Kuznetsov, 2003; Kuznetsov & Kuznetsova, 2003). The holotype of Lycodon calcarophilus sp. nov. was encountered at dusk (18h00) near the entrance of a terrestrial karst cave. At the time of observation, the individual was actively engaged in predatory behaviour, targeting a skink tentatively identified as Scincella cf. rufocaudata (Darevsky & Nguyen) . The species appears to have a restricted distribution and is likely rare, as suggested by the very limited number of observations during fieldwork. It is a nocturnal snake, typically observed actively foraging on rocky substrates or low vegetation such as small tree branches, suggesting a degree of arboreal capability. The new species inhabits primary limestone forests at elevations ranging from approximately 200 to 250 m asl. A list of amphibian and reptile species found in sympatry with Lycodon calcarophilus sp. nov. in Phong Nha-Ke Bang NP is provided in Appendix Table S6.

Conservation status. Lycodon calcarophilus sp. nov. is currently known only from protected areas in central Vietnam. This is a secretive and presumably rare species that appears to be a strict forest specialist, restricted to undisturbed primary limestone forests. Its apparent dependence on intact karst forest habitats suggests vulnerability to habitat degradation. The type locality, situated within Phong Nha-Ke Bang NP, benefits from relatively effective protection and retains extensive tracts of primary forest. However, the species is likely to occur in adjacent limestone massifs outside the park boundaries, where forest habitats are increasingly threatened by anthropogenic activities. These areas are subject to ongoing deforestation, habitat fragmentation, and land-use conversion, including the expansion of Acacia auriculiformis (A.Cunn. ex Benth.) , A. mangium (Willd.) , and A. holosericea (A.Cunn. ex G.Don) plantations, as well as infrastructure development and human settlement. Additional pressures from unregulated livestock grazing further exacerbate habitat degradation. Given the limited data on the species broader distribution, population size, and trends, we recommend that Lycodon calcarophilus sp. nov. be classified as Data Deficient (DD) under the IUCN Red List Categories and Criteria ( IUCN Standards and Petitions Committee 2024), until further field surveys can clarify its threatened status.