Trimeresurus albolabris, Gray, 1842

Chandramouli, S. R., Campbell, Patrick D. & Vogel, Gernot, 2020, A new species of green pit viper of the genus Trimeresurus Lacépède, 1804 (Reptilia: Serpentes: Viperidae) from the Nicobar Archipelago, Indian Ocean, Amphibian & Reptile Conservation (e 264) 14 (3), pp. 169-176 : 170-174

Trimeresurus albolabris – Smith (1943) part, Vogel (2008) part, Vogel et al. (2014) part.

10–12 supralabials; 12–15 infralabials; two internasals usually in contact with each other; 11–14 cephalic scales; relative tail length (TaL/TL) ranging from 0.143–0.20; dorsal and ventral verdant green in color, lacking white ventrolateral stripes; males with a white supralabial streak, bordered by a reddish tinge above; a pair of white and red stripes along the sides of the tail in both males and females; a reddish brown colored tail and a greenish iris; hemipenis reaching the 13 th caudal plate.

Holotype. BNHS 3304 , an adult female from Chuckchucka Village (9.2161ºN, 92.8109ºE, 14 m asl), Car Nicobar, collected by a group of Nicobari men (fide Vijayakumar and David 2006).

Paratypes. DOSMB 05104 , an adult male from Chuckchucka Village , Car Nicobar ; NHMUK 1936.7 .7.40, NHMUK 1936.7 .7.41, NHMUK 1936.7 .7.42, (three adult females from ‘Car Nicobar, Nicobar Is.’), NHMUK 1936.7 . 7.46 an unsexed adult from ‘ Car Nicobar , Nicobar Is .,’ NHMUK 1936.7 .7.47 and NHMUK 1936.7 . 7.48 (two adult males from ‘ Nicobar Is. ’ and ‘ Andaman Is. ’ [doubtful], respectively), collected during Lord Moyne’s expedition to the Nicobar Islands .

Etymology. The specific epithet is a patronym, named in genitive singular case, honoring Patrick David, an eminent reptile taxonomist for his immense contribution to the systematics of Asian pit vipers and, in particular, to the Nicobar snake fauna.

Diagnosis. Trimeresurus davidi sp. nov. is an arboreal member of the genus Trimeresurus restricted to the Car Nicobar Island of the Nicobar archipelago, characterized by: medium to large sized body (277–835 mm SVL); dorsal scales in a series of 21–25:21–23:15–17 rows; nasal partly fused with the first supralabial; 166–179 ventrals; 46–70 subcaudals; one preocular; 2–3 postoculars; Description of the holotype. BNHS 3304, an adult female, in a fairly good state of preservation. Head large (HL/SVL 0.05), longer than broad (HL/HW 1.41); triangular in shape and fairly distinct from a slender neck. Nostrils situated more towards the snout tip than the eyes (EN/ES 0.87). Eyes relatively small and oval (ED/HL 0.2), with a vertically elliptical pupil. Dorsal and lateral head scales smooth and imbricate. Rostral barely visible from above; followed by two large intranasals not in contact with each other. Fourteen cephalic scales in a line between the two elongated supraoculars. Nasal partially fused with the 1 st supralabial; 12/12 supralabials; 3 rd largest; 14/14 infralabials, of which, the first three contact the anterior chin shields. Loreal pit large and triangular. Two small postoculars; one preocular and crescent shaped subocular scales on either side of the head. Dorsal scales in 23:23:15 rows; with very feeble median longitudinal keels. Ventrals 173; broad and extending throughout the width of the belly; anal single; subcaudals 61; divided. Temporal scales small and smooth. Tail relatively short (TaL/TL 0.146) and prehensile.

Overall dorsal coloration dark grey in preservation, with a pale grey venter. Ventral surface of the tail lighter in color, bearing two incomplete white lateral stripes along the sides. Dorsal surface of the tail is a different color than the body, and of a lighter shade when compared to the body. Ventrolateral stripes absent on the body; white ventrolateral stripes present along the sides of the tail extending from the vent to the 13 th subcaudal.

Variation. Measurements and scale counts of the paratypes and referred material are given in Table 1. Mid-body scale rows range from 21–25:21–23:15–17; ventrals range from 170–179 in males and 166–178 in females. Subcaudals range from 67–70 in males and 55– 64 in females. Internasals usually in contact with each other, but separated by a small scale in one specimen. Cephalic scales range from 11–14; postoculars range from 2–3. Relative tail length in males: 0.178 –0.200; in females: 0.143 –0.161. Sexual dimorphism apparent in body for the tail dimensions and the number of subcaudals. Verdant green colored in life, both dorsally and ventrally, without a white ventrolateral pair of stripes along the sides of the body; but with a pair of white and red lateral stripes along the sides of the tail. Males have a thin white labial stripe bordered by red above the supralabials on either side of the head (absent in females) and a white stripe bordered by red along the subcaudals from the vent until about half the length of the tail (also present in females).

Natural history and distribution ( Fig. 3 ). Five individuals of T. davidi sp. nov. were encountered during this study. They were always observed as active and foraging during the night (2100 h and later) and were never encountered during the day. Individuals were seen on shrubs at heights ranging from 1.20 m (n = 2) to about 8 m (n = 1) above the ground; also seen on the rocky walls of old buildings (n = 1). One was found dead in a coconut plantation, presumably killed by someone. The large (~ 120 cm) female individual observed on the top of a tree at a height of about 8 m had a swollen anterior belly, indicating that it had fed recently. Lizards of the genera Coryphophylax, Bronchocela, Cyrtodactylus , and Gehyra were observed at close quarters (~ 2 m) from the point where the snakes were sighted. Other relatively small-bodied, endemic species of snakes, namely T. labialis (Fitzinger in: Steindachner, 1867) and Lycodon tiwarii Biswas and Sanyal, 1965 , were observed to be sympatric with T. davidi sp. nov. and could be potential competitors as they are also nocturnal snakes feeding on prey species similar to T. davidi sp. nov.

Comparison. Trimeresurus davidi sp. nov. does not have any superficially similar looking, green-colored arboreal congeners on Car Nicobar Island, on which its distribution is restricted. It can be distinguished from other members of the T. albolabris complex by the following combination of characters: dorsal scales of T. davidi sp. nov. in 21–25:21–23:15–17 rows (vs. 21– 23:19–21: 15 in T. albolabris and T. insularis , 21:21: 15 in T. caudornatus , 21:19: 17 in T. septentrionalis , and 21:19: 15 in T. salazar ). There is some overlap in this character, as is expected; however, five of the 11 (45%) examined T. davidi specimens had 23 dorsal scale rows at midbody. This character has never been recorded in any of the other species within this complex. Also, there seems to be a certain degree of overlap in scalation characters between the currently recognized members of T. albolabris complex, which makes the partially overlapping values with T. davidi sp. nov. quite understandable. Trimeresurus davidi sp. nov. has 166– 179 ventrals (vs. 149–173 in T. albolabris , 161–163 in T. caudornatus , 160–181 in T. septentrionalis , 156–167 in T. insularis , and 163–171 in T. salazar ); an absence of white ventrolateral stripes along the body in T. davidi sp. nov. (vs. present in T. septentrionalis and T. salazar ); and the presence of a pair of red and white ventrolateral stripes along the sides of the tail (vs. absent in all other species). Trimeresurus davidi sp. nov. is considerably larger than all other species of this complex. For further comparisons, see also the morphological characters ( Table 2) for the material examined (Appendix 1) in this study.

From the two other sympatric congeners, T. andersoni Theobald, 1868 and T. labialis Fitzinger in: Steindachner, 1867, T. davidi sp. nov. can be distinguished by its verdant green dorsal coloration (vs. predominantly brown in both T. andersoni and T. labialis ); midbody dorsal scales in 21–23 rows (vs. 23–25 in T. andersoni , 23 in T. labialis ); and the first supralabial united with the nasal in T. davidi sp. nov. (vs. separate in T. labialis ).

Additionally, from the green color morph of Trimeresurus cantori (Blyth 1846) which occurs on islands of the central group of the Nicobar archipelago, T. davidi sp. nov. can be distinguished by a lower number of mid-body scale rows (21–23 in T. davidi sp. nov. vs. 25–29 in T. cantori ); and the absence of a pair of white ventro-lateral stripes along the sides of the body in T. davidi sp. nov. (vs. present in T. cantori ) [ Whitaker and Captain 2008].

Figures

Fig. 3. Distribution of members of the Trimeresurus albolabris complex showing the type locality and distribution of T. davidi sp. nov.