Trimeresurus cyanolabris, Idiiatullina & Nguyen & Bragin & Pawangkhanant & Le & Vogel & David & Poyarkov, 2024

Idiiatullina, Sabira S., Nguyen, Tan Van, Bragin, Andrey M., Pawangkhanant, Parinya, Le, Dac Xuan, Vogel, Gernot, David, Patrick & Poyarkov, Nikolay A., 2024, A new species of green pitviper of the Trimeresurus macrops complex (Reptilia: Serpentes: Viperidae) from South Central Coastal Region of Vietnam, Zootaxa 5474 (4), pp. 375-411 : 381-386

Trimeresurus cyanolabris sp. nov. ( Fig. 3–4 ; Tables 2 , 4–6 )

Chresonymy:

Trimeresurus albolabris (non Trimeresurus albolabris Gray, 1842 ) — Nemes et al. (2013: 320); Nguyen et al. (2019: 40, in part).

Trimeresurus macrops (non Trimeresurus macrops Kramer, 1977 ) — Hoang et al. (2019: 90).

Trimeresurus (Trimeresurus) macrops — Poyarkov et al. (2023: 391, in part).

Trimeresurus stejnegeri (non Trimeresurus stejnegeri Schmidt, 1925 ) — Hoang et al. (2019: 91).

Holotype. ZMMU Re-17679 (field ID NAP-13705), adult male, from Nui Chua National Park in Thai An Village , Vinh Hai Commune, Ninh Hai District, Ninh Thuan Province, Vietnam (11.77757°N, 109.17603°E; altitude 155 m a.s.l.) collected by N.A. Poyarkov and A.M. Bragin from the ground on the bank of a mountain stream on March 8, 2023.

Paratypes (n = 9). ZMMU Re-17678 (field ID NAP-13704), adult male, collected on March 8, 2023, from the same location as the holotype ; ZMMU Re-17680–81 (field ID NAP-13229–30), two adult females, collected by N.A. Poyarkov and D. X. Le on January 6, 2023, from the valley of Nuoc Ngot River (11.778°N, 109.176°E; altitude 280 m a.s.l.), ca. 3 km south-west from Nuoc Ngot Beach, on the territory of Nui Chua N.P., Thai An Village, Vinh Hai Commune, Ninh Hai District, Ninh Thuan Province, southern Vietnam ; ZMMU Re-17682 (field ID NAP-13643), adult female, collected from Nui Chua N.P. in Thai An Village , Vinh Hai Commune, Ninh Hai District, Ninh Thuan Province, Vietnam (11.72343°N, 109.13656°E; altitude 730 m a.s.l.) by N.A. Poyarkov and A.M. Bragin on March 4, 2023 ; ZMMU Re-17683–84 (field ID NAP-13365–66), two adult females, collected from Phuoc Binh N.P., Phuoc Binh Commune , Bac Ai District, Ninh Thuan Province, Vietnam (11.99353°N, 108.74379°E; altitude 400 m a.s.l.) by N.A. Poyarkov and A.M. Bragin on February 25, 2023 ; DTU 605 (adult female) from a secondary forest near Hon Ba NR, Suoi Cat Commune, Cam Lam District, Khanh Hoa Province, Vietnam (12.134169°N, 109.034452°E; altitude 130 m a.s.l.) collected by T.V. Phan, T.D. Nguyen and T.V. Nguyen on May 15, 2023 ; DTU 606 (adult female) from An Chua Area , Diem Khanh Distrist, Khanh Hoa Province, Vietnam (12.327065°N, 109.098045°E; altitude 90 m a.s.l.) collected by T.V. Phan, T.D. Nguyen, and T.V. Nguyen on May 20, 2023 ; DTU 650 (adult female) collected by T.V. Phan, T.D. Nguyen, and T.V. Nguyen from Hon Heo Island , Ninh Da Commune, Ninh Hoa District, Khanh Hoa Province, Vietnam (12.397168°N, 109.294047°E; altitude 45 m a.s.l.) on May 19, 2023 .

Additional materials (n = 3). ZFMK 94670 (adult male) from Ba To District , Quang Ngai Province, Vietnam (ca. 14.707444°N, 108.997215°E; altitude 140 m a.s.l.) . DTU 653 (adult female, released) from Suoi Mo Area , Bui Thi Xuan Town, Quy Nhon City, Binh Dinh Province, Vietnam (13.695361°N, 109.170546°E; altitude 280 m a.s.l.) collected by T.V. Phan and T.D. Nguyen on August 03, 2023 ; DTU 636 (adult female, released) from Hiep Ha Commune , Van Canh District, Binh Dinh Province, Vietnam (13.664300°N, 108.972583°E; altitude 250 m a.s.l.) collected by T.V. Phan and T.D. Nguyen on August 10, 2023 .

Etymology. The specific name “ cyanolabris ” is formed of the Latin adjective “ cyaneus,” derived from a Latizined form of the classical Greek adjective κυαΝΟΣ (kyanos), meaning “dark blue” or “deep blue,” and of the Latin noun “labrum” (- i), the lip. This specific name means “deep blue-lipped,” and refers to the distinctive blue color found on the throat, chin, and infralabials of the new species. Though traditionally it is recommended that the Greek and Latin words not be combined in one species nomen, we would like to underline that the adjective “ cyaneus ” is common in Latin texts and can be regarded as a proper Latin adjective. We suggest the following common English name: “Blue-lipped Green Pitviper”, Russian name: “Golubogubaya bambukovaya kufiya”, and Vietnamese name: “Rắn lục mép xanh dƯƠng”.

Diagnosis. The new species is assigned to the subgenus Trimeresurus based on the following morphological attributes: a long calyculate hemipenis and a partially fused first supralabial and nasal scales ( Malhotra & Thorpe 2004 [as Cryptelytrops ]; David et al. 2011). The new species, Trimeresurus cyanolabris sp. nov., differs from other members of the subgenus Trimeresurus by the combination of the following morphological characters: small size, maximum known SVL of 638 mm; dorsal scales in 21 (rarely 23)–21–15 rows, moderately keeled except the outermost rows; ventral scales 166–178; subcaudal scales 52–75, all paired; hemipenis forked, calyculate, reaching the 8 th subcaudal; eye bright yellow in both sexes; dorsal surfaces deep green lacking cross-bands; postocular streak white in both sexes; ventrolateral stripe, faint, present on the first few dorsal scale rows in males, absent in females; throat, chin, and lower labials blue color.

Description of the holotype. Adult male ( Fig. 3 ), specimen in a good state of preservation. Body cylindrical, long, and thin (SVL 464 mm, TaL 106 mm, TL 570 mm, TaL/TL 0.186) ( Fig. 3A–B ). Head triangular in dorsal view ( Fig. 3C ), elongate, clearly distinct from the neck (HL 21.2 mm; HW 13.0 mm; HW/HL ratio 0.61). Snout elongate, flattened, and rounded in dorsal view ( Fig. 3C ), rather rectangular in lateral view ( Fig. 3E–F ), with a very distinct and sharp canthus rostralis. Eyes large (ED 3.5 mm; EN 5.2 mm; ED/EN ratio 0.67). Rostral slightly visible in dorsal aspect, triangular ( Fig. 3C ). Pupil vertically elliptical, loreal pit present, triangular in shape ( Fig. 3E–F ). Nostril completely enclosed in nasal scale; nasal scale partially fused with first supralabial ( Fig. 3E–F ). Shield bordering the anterior edge of the loreal pit fused with second supralabial, which is tall. Anterior subocular long, thin, crescentlike, separated from the 4 th and 5 th supralabials by one row of scales; posterior subocular ovoid, separated from the 6 th supralabial by 2/1 scales ( Fig. 3E–F ). Three preoculars on each side of the head; two upper preoculars located above the loreal pit, elongate, in contact with the single loreal, which separates them from the nasal; lower preocular forming the lower margin of the loreal pit, lower preocular in contact with third supralabial ( Fig. 3E–F ). A small scale between nasal and second supralabial; 2/2 postoculars; 10/10 supralabials, third the largest ( Fig. 3E–F ); 12/12 infralabials, those of the first pair in contact with each other behind the mental; the first three pairs of infralabials in contact with the single pair of chin shields ( Fig. 3E–F ). Six pairs of gulars aligned between the chin shields and the first preventral ( Fig. 3D ). One large pair of enlarged internasals, separated by three small scales. One supraocular, large ( Fig. 3C ). Scales on snout and in the interorbital region smooth, irregular, subimbricate; temporal and occipital scales feebly keeled ( Fig. 3 E-F). Dorsal scales in 21–21–15 rows, moderately keeled, except the first row, which is smooth ( Fig. 3A ). One preventral and 175 ventrals. Anal plate single; 72 subcaudals, all divided. Hemipenes long, papillose, and deeply forked with small, soft basal spines, reaching the 8 th subcaudal ( Fig. 3B ).

Coloration. In life ( Fig. 4A ), the body is uniformly bright grass-green above and on the upper part of the sides and gradually turns yellow on the lower sides, without a ventrolateral stripe. Tail dull brick red, dorsally extending as far as vent, with a faint margin on lateral side of tail. Venter light greenish-yellow, paler in its anterior part, and light green in its posterior part. The dorsal surface of the head and the temporal region are green without a postocular streak; supralabial, infralabial, chin and throat regions are blue. Iris bright yellow. In preservative ( Fig. 3 ), the background dorsal color faded to a light gray; the ventral color became white.

Variation (for detailed information, see Table 5 ). The longest known specimen is 743 mm long (SVL 638 mm, TaL 105 mm; female, DTU 635); the longest known male is 607 mm long (SVL 478 mm, TaL 129 mm; ZFMK 94670). Ratio TaL/TL: 0.129 –0.213 (males: 0.181 –0.213, females: 0.129 –0.154).

Body scalation. 21 (rarely 23 in the ZMMU Re- 176 Paratype)–21–15 DSR; 166–178 VEN, without sexual dimorphism; 52–75 SC (males: 71–75, females: 52–62); total number of VEN +SC: 223–247 (males: 241–247, females: 223–237).

Head scalation. InSep: none, internasals in contact in all known specimens; Cep: 9–10; SL: 10 (exceptionally 9 or 11); IL: 10–13.

Main characters of the pattern. The postocular streak is always absent in both sexes; ventrolateral stripe present, white, faint, and thin in males; absent in females. Eyes bright yellow in both sexes.

Comparisons. The new species is phylogenetically placed within the subgenus Trimeresurus ( Malhotra & Thorpe 2004 [as Cryptelytrops ]; David et al. 2011) and is morphologically most similar to other green pitviper species from the T. macrops complex, including T. rubeus , T. cardamomensis , and T. macrops ; therefore, the comparisons with these three species appear to be the most pertinent. The main diagnostic characters separating Trimeresurus cyanolabris sp. nov. from these three species are summarized in Table 6 .

Trimeresurus cyanolabris sp. nov. is distinguished from T. rubeus (restricted to southern Vietnam and eastern Cambodia) by having: (1) lower max SVL in males (478 mm vs. 586 mm), but higher max SVL in females (638 mm vs. 503 mm); (2) slightly lower ratio TaL/TL in both sexes (0.18–0.21 [X = 0.19] in males, 0.13–0.15 [X = 0.14] in females vs. 0.21–0.22 [X = 0.22] in males, 0.15–0.19 [X = 0.17] in females); (3) slightly higher ratio HW/HL in both sexes (0.55–0.68 [X = 0.61] in males, 0.65–0.70 [X = 0.66] in females vs. 0.53–0.60 [X = 0.56] in males, 0.46–0.72 [X = 0.61] in females); (4) slightly higher ratio ED/EN in males (0.67–0.78 [X = 0.74] vs. 0.66–0.74 [X = 0.70], but lower ratio ED/EN in females (0.62–0.88 [X = 0.71] vs. 0.79–0.95 [X = 0.85]; (5) slightly higher number VEN in both sexes (166–175 [X = 171.0] in males, 169–178 [X = 174.1] in females vs. 164–171 [X = 167.5] in males, 158–163 [X = 159.8] in females); (6) slightly lower number SC in males (71–75 [͞x =72.7] in males, 52–62 [X = 57.7] in females vs. 78–80 [X = 79.0] in males, 52–69 [X = 61.6] in females; (7) slightly lower total number of VEN+SC in females (223–237 [X = 231.8] vs. 214–228 [X = 221.4]; (8) without postocular white stripe in males (vs. present); (9) ventrolateral body stripe present, faint, poorly contrasted in males (vs. well developed, highly contrasted with reddish and white); (10) ventral surface of body greenish-blue (vs. greenish-yellow); (11) eye color bright yellow in both sexes (vs. bright red, blood-red or deep reddish–orange in both sexes).

Trimeresurus cyanolabris sp. nov. further differs from T. cardamomensis (restricted to southwestern Cambodia, southeastern Thailand, and the southermost part of Vietnam) by having: (1) lower max SVL in males (478 mm vs. 535 mm), but higher max SVL in females (638 mm vs. 536 mm); (2) slightly lower ratio ED/EN in both sexes (0.67–0.78 [X = 0.74] in males, 0.62–0.88 [X = 0.71] in females vs. 0.66–0.91 [X = 0.78] in males, 0.51–0.97 [X = 0.74] in females); (3) slightly higher number of SC in males (71–75 [X = 72.7] vs. 60–75 [X = 67.0]); (4) higher total number of VEN+SC in males (241–247 [X = 243.7] vs. 226–243 [X = 234.0]); (5) postocular stripe absent in males (vs. present, white or blue); (6) ventrolateral body stripe present, faint, poorly contrasted in male (vs. well developed, highly contrasted, white); (7) ventral surface of body greenish-blue (vs. greenish-yellow); (8) head shape more elongate-oval (vs. more triangular); (9) small size scales on head behind internasal scales (vs. lager). Furthermore, T. cyanolabris sp. nov. is widely separated from T. cardamomensis on a geographical basis, as the latter species inhabits only southeastern Thailand, southerwestern Cambodia, and southernmost Vietnam (Phu Quoc Isl.). Moreover, T. rubeus separates the ranges of both species..

In particular, Trimeresurus cyanolabris sp. nov. is distinguished from T. macrops by having: (1) lower max SVL in males (478 mm vs. 557 mm), but higher max SVL in females (638 mm vs. 629 mm); (2) slightly lower ratio HW/ HL in males (0.55–0.68 [X = 0.61] vs. 0.56–0.82 [X = 0.68]); (3) lower ratio ED/EN in both sexes (0.67–0.78 [X = 0.74] in males, 0.62–0.88 [X = 0.71] in females vs. 0.62–1.12 [X = 0.89] in males, 0.64–0.97 [X = 0.83] in females); (4) slightly higher number VEN in both sexes (166–175 [X = 171.0] in males, 169–178 [X = 174.1] in females vs. 158–173 [X = 165.0] in males, 159–173 [X = 166.4] in females); (5) higher total number of VEN +SC in both sexes (241–247 [X = 243.7] in males, 223–237 [X = 231.8] in females vs. 225–240 [X = 233.0] in males, 214–235 [X = 222.1] in females); (6) postocular stripe absent in males (vs. present); (7) ventrolateral body stripe present, faint, poorly contrasted in male (vs. well developed, highly contrasted); (8) ventral surface of body greenish-blue (vs. greenish-yellow).

Among the other species in the subgenus Trimeresurus , the new species can be readily distinguished from: T. ciliaris Idiiatullina, Pawangkhanant, Tawan, Worranuch, Dechochai, Suwannapoom, Nguyen, Chanhome & Poyarkov , T. fasciatus (Boulenger) , T. labialis Fitzinger in Steindachner, T. mutabilis Stoliczka , T. honsonensis , T. kraensis Idiiatullina, Pawangkhanant, Suwannapoom, Chanhome, Nguyen, David, Vogel & Poyarkov , T. kanburiensis , T. kuiburi , and T. venustus by coloration and pattern (uniform green vs. reddish-brown or purple or dark olive-brown bands on emerald-green or olive-greyish background).

Trimeresurus cyanolabris sp. nov. can be distinguished from Trimeresurus andersoni Theobald , T. ayeyarwadyensis , T. cantori (Blyth) , T. erythrurus , and T. purpureomaculatus (Gray) by the lower number of midbody dorsal scale rows (21 vs. 23–25 in T. andersoni and T. ayeyarwadyensis , 25–29 in T. cantori , 23 (rarely 24, 25) in T. erythrurus , 25 (rarely 27, 29) in T. purpureomaculatus ). The new species can be distinguished from: T. caudornatus Chen, Ding, Vogel & Shi ; T. davidi Chandramouli, Campbell & Vogel ; T. guoi Chen, Shi, Vogel & Ding ; T. insularis Kramer ; T. salazar Mirza, Bhosale, Phansalkar, Sawant, Gowande & Patel ; T. septentrionalis Kramer , T. uetzi Vogel, Nguyen & David by having: body size smaller (max SVL 638 mm vs. 804 mm in T. caudornatus , 835 mm in T. davidi , 804 mm in T. guoi , 735 mm in T. insularis , 819 mm in T. septentrionalis , 689 mm in T. uetzi ); in contrast, body size larger (max SVL 638 mm vs. 565 mm in T. salazar ); throat, chin, and lower labials in shades of blue (vs. creamy or white); relatively larger size of the eye (most obvious in adults); relatively wider supraoculars; the shape of the head (widens quite abruptly behind the eyes vs. more elongate or oval).

Lastly, Trimeresurus cyanolabris sp. nov. was previously misidentified with T. albolabris and T. stejnegeri Schmidt (see Nguyen et al. 2009; Hoang et al. 2019). The new species can be distinguished from T. albolabris by: body size smaller (max SVL 638 mm vs. 749 mm); relatively larger size of the eye, the relatively wider supraoculars, and the shape of the head (widens quite abruptly behind vs. more elongate or oval); it is distinguished from T. stejnegeri by the 1 st supralabial fused with nasal (vs. entirely separated by a suture); body size smaller (max SVL 638 mm vs. 720 mm); no postocular stripe in males (vs. present); eye color bright yellow in both sexes (vs. in shades of red in both sexes).

Distribution. Currently, Trimeresurus cyanolabris sp. nov. is known from the southern and central parts of coastal Vietnam (from Ba To District in Quang Ngai Province; from Quy Nhon City and Van Canh District in Binh Dinh Province; from Diem Khanh District, Ninh Hoa Town, and Hon Ba NR in Cam Lam District in Khanh Hoa Province; from Nui Chua NP in Ninh Hai District and Phuoc Binh NP., Bac Ai District in Ninh Thuan Province) ( Fig. 1 , Appendix III). The occurrence of the new species in the Dak Lak and Phu Yen provinces of Vietnam is strongly anticipated. The actual extent of its distribution is still unknown.

Natural history. Trimeresurus cyanolabris sp. nov. was recorded from relatively low- to mid-elevations (ca. 90–400 m a.s.l.) in tropical dry forests of the central southern region of Vietnam ( Poyarkov et al. 2023). The male holotype ZMMU Re-17679 was collected from the ground near a small mountain stream; the male paratype ZMMU Re-17678 while perching on a bush ca. 40 cm above the ground; two female paratypes ZMMU Re-17680–81 were collected on the ground (large flat stones) on the bank of a small river (see Fig. 5 ); the female paratype ZMMU Re-17682 was collected while perching on a tree branch ca. 1 m above the ground, while female paratypes ZMMU Re-17683–84 were collected from the ground in the tropical montane forests on the leaf litter; all specimens were recorded between 1700 h and 2300 h. Therefore, the new species is semi-arboreal with crepuscular and nocturnal activity. During the day, it often perches on the branches or in the hollows of trees 0.5–1.5 m high near streams. In Khanh Hoa Province, it is common in the beginning (August) and at the end of the rainy season (October), often in the lower layers of trees or on dry branches under the trees, in contrast to T. albolabris which usually occurs at higher tree levels. There may be an ecological stratification between these two species in the Khanh Hoa population (T.V. Phan pers. comm.). The new species feeds on small frogs and small lizards (such as Gekko sp. ) (T.V. Nguyen pers. obser.). Nothing is known about its reproduction cycle.

Conservation status. Further research is required to clarify the extent of the distribution, population size, trends, and conservation status of the new species. Trimeresurus cyanolabris sp. nov. is distributed over a large area, including several protected zones. Across its range, the new species seems to be quite common, especially in Khanh Hoa Province, where many local people and tourists have observed and reported it through the social networking group “Snake Identification and First Aid for Snakebites in Vietnam ” (SIFASV, Vietnam, T.V. Nguyen pers. obser.) Thus, we tentatively suggest that Trimeresurus cyanolabris sp. nov. should be considered a Least Concern (LC) following the IUCN‘s Red List categories (IUCN Standards and Petitions Committee 2019).

Figures

FIGURE 1. Distribution of the green-colored members of the Trimeresurus macrops species complex in Indochina. Colors of icons and locality numbers correspond to those of Fig. 2 and Appendix III. Stars indicate the type localities; circles indicate the localities of specimens that were used in phylogenetic analysis; (for the Trimeresurus cyanolabris sp. nov. specimens from the type locality were included in the phylogenetic analysis) and triangles indicate distribution records (see Appendix III).

FIGURE 3. The holotype of Trimeresurus cyanolabris sp. nov. in preservative (ZMMU Re-17679, adult male) from Nui Chua NP, Ninh Thuan Province, Vietnam. A dorsolateral and B ventral view of body; C head in dorsal, D in ventral, E in lateral right, and F in lateral left aspects. Scale bar equals 1 cm. Photographs by S.S. Idiiatullina.

FIGURE 4. Type specimens of Trimeresurus cyanolabris sp. nov. in life from Nui Chua NP, Ninh Thuan Province, Vietnam: A holotype ZMMU Re-17679, adult male; B paratype ZMMU Re-17681, adult female. Photographs by A.M. Bragin (A) and N.A. Poyarkov (B).

FIGURE 5. Habitat of Trimeresurus cyanolabris sp. nov. in Nui Chua NP, Ninh Thuan Province, Vietnam. Photograph by A. M. Bragin.