Trimeresurus mutabilis Stoliczka, 1870

Vogel, Gernot, David, Patrick & Chandramouli, S. R., 2014, On the systematics of Trimeresurus labialis Fitzinger in Steindachner, 1867, a pitviper from the Nicobar Islands (India), with revalidation of Trimeresurus mutabilis Stoliczka, 1870 (Squamata, Viperidae, Crotalinae), Zootaxa 3786 (5), pp. 557-573 : 564-569

Trimeresurus mutabilis Stoliczka, 1870 New status

( Figs. 3 & 4 ; Table 2 )

Trimeresurus mutabilis Stoliczka, 1870a: 107 .— Onomatophore. Lectotype, by present designation, NMW 14863:1 (adult male); collected in 1869 and deposited by F. Stoliczka in 1874.— Type locality. Restricted by virtue of lectotype designation (see above), to Camorta Island, Nicobar Archipelago, India (originally 14 syntypes, see above).— Status. Here resurrected at the species level from the synonymy of Trimeresurus labialis Fitzinger in Steindachner, 1867.

Trimeresurus labialis (non Fitzinger in Steindachner, 1867)— Smith (1943) (part)

Trimeresurus labialis — Das, 1994; 1999b (part)

Trimeresurus labialis — Vijayakumar & David, 2006 (part)

Trimeresurus labialis — Whitaker & Captain (2008) (part)

Material (n = 27). Nicobar Archipelago. Bompoka Island. BNHS 3326, ZSI 255547.—Camorta Island. BMNH 1940.3.9.50, BNHS 3338, NMW 14863:1–14863:6, ZSI 3083–3087 (all original syntypes; see above for their locality, precisely specified in this work), ZSI 255548.—Chowra Island. ZSI 255551.—Katchal Island. BNHS 3331.—Nancowry Island. BNHS 3332–3333, ZSI 255552.—Trinket Island. BNHS 3334–3335, ZSI 255554–ZSI 255555.—No precise locality. BMNH 1936.7.7.44, “ Car Nicobar?” (locality doubtful) - BNHS 3330, BNHS 3336–3337, SKMCBT 31, ZSI 2950–2951, “Nicobars” - USNM 29644, “Central Nicobars”.

Comments. Trimeresurus mutabilis was recognized as valid by Theobald (1876: 223) before Boulenger (1890: 430) placed it in synonymy of his Lachesis gramineus (Shaw, 1802) . Sclater (1891: 72) also regarded this species as a synonym of Trimeresurus gramineus . Werner (1926: 253) recognized it as a valid species but Smith (1943: 525) placed it in the synonymy of Trimeresurus labialis Fitzinger in Steindachner, 1867, a position followed by all subsequent authors. On the basis of morphological analyses detailed above, we here resurrect this taxon as a valid species. It belongs to the genus and subgenus Trimeresurus Lacépède, 1804 . It is monotypic.

Diagnosis. A small pitviper of the genus Trimeresurus with (1) First supralabial entirely separated from nasal; (2) 21 rows at midbody; (3) internasals always separated each from the other; (4) 154–164 Ve, 46–60 SC; (5)10–12 cephalics between supraoculars; (6) total length up to 510 mm; (7) a strong dimorphism in relative tail length (see below); and (8) two morphs of dorsal colouration and pattern, either with conspicuous dark dorsal crossbands on a grey or brown background, or more or less uniformly brown or rusty-brown with red spots ( Table 1).

Description of the lectotype. NMW 14863:1, adult male, from Camorta Island, Nicobar Archipelago, India; collected in 1869 and deposited by F. Stoliczka in 1874.

Morphology. Body moderately elongate; head triangular, thick but flattened, wide at its base and clearly distinct from the neck; snout average, 1.7 times as long as diameter of eye, flattened, rounded and narrow when seen from above, truncated when seen from lateral side, with a distinct canthus rostralis; eye rather large, eye diameter 1.2 times the distance between the lower margin of eye and upper lip border; tail rather long, tapering.

SVL 351 mm, TaL 74 mm, TL 425 mm; HL 19.9 mm; Ratio TaL / TL 0.174.

Body scalation. DSR 21 - 21 - 15 scales, rhomboid, smooth; VEN 158 (+ 1 preventral), SC 61, all paired; anal entire.

Head scalation. Rostral wider than high, triangular, visible from above; nasal subrectangular, undivided, with nostril in its middle; one pair of moderately enlarged, subrectangular internasals, 1.4 times wider than deep, about twice as wide as and longer than adjacent upper snout scales, separated each from the other by 1 small scale; 4 /4 canthal scales bordering the canthus rostralis between internasal and corresponding supraocular, enlarged compared with adjacent snout scales; one small triangular loreal between upper preocular and nasal; two upper preoculars above loreal pit, lower one bordering the upper margin of loreal pit, upper one visible from above, both elongated and in contact with loreal; lower preocular forming lower margin of loreal pit; 1/1 supraocular, elongate and narrow, in total about 3 times as long as wide, not much wider than the adjacent upper head scales, 0.7 times as wide as internasals, not indented by upper head scales; scales on dorsal surface of head small, smooth, irregular in shape, larger on snout than in the frontal area; 10 scales in a line between supraoculars; scales on the occiput flat and smooth; temporals smooth; 2/2 postoculars; 1/1 thin, elongated, crescent-like subocular; 10/ 10 SL, comparatively large 1st SL and nasal completely fused at left, partly divided at right by an incomplete and shallow furrow, 2nd SL tall, in contact with nasal and forming the anterior border of loreal pit, 3rd SL largest, elongate, about 1.25 times longer than high, in contact with subocular at left, separated at right by 1 minute scale, 4th SL about 0.7 times lower than third one, separated from subocular by 1/1 small scale, 5th and other posterior SL separated from subocular by 1 scale at left, 2 at right; 13 /12 IL, first pair in contact with each other, 1st–3rd pairs in contact with chin shields; 8 rows of smooth gular scales; chin shields regularly arranged.

Coloration and pattern. The body is greyish-brown, slightly paler on the lower parts of the sides (the parts appearing olive green or reddish-brown on Fig. 3 & 4 are caused by artifacts due to the damage of the epidermis), with some very faint dark crossbands, visible only in good light. No pale ventrolateral stripes. The tail is as the body, with a faint, diffuse vertebral pinkish-grey stripe (red in life?), widening on the posterior part of the tail, the posterior quarter of which is entirely pinkish-gray.

Head deep greenish-blue on the dorsal and temporal regions, slightly darker than the body; supralabials in the shades of blue, barely lighter than the upper head surface; a short, diffuse white temporal streak extending behind the eye on the 2nd row of temporals above the last posterior supralabials; mental, infralabials and chin shields are light bluish-grey.

The venter is uniformly pale bluish-white, darker and more distinctly deep blue on the outer parts of ventrals. The tail is as the body anteriorly, becoming pinkish-grey near its tip.

This specimen belongs to second morph of coloration and pattern of this species (see below).

Species description and variation. Body moderately elongated, thicker in females; the triangular head is rather long, flat, wide at its base and clearly distinct from the neck; the snout rather long and narrow, 1.4–1.8times as long as eye diameter, flattened, rounded when seen from above, obliquely truncated seen from the side, with a distinct canthus rostralis; eye average to large, with a diameter 1.0–1.3 times the distance lower eye margin-lip margin; the tail is cylindrical, average, tapering progressively and strongly prehensile.

The maximal recorded total length is 510 mm (SVL 435 mm; TaL 75 mm; ZSI 255554, female). The longest known male is 425 mm long (SVL 351 mm, TaL 74 mm; NMW 14863:1, lectotype) but we have examined a specimen, the tail of which is incomplete, with a SVL of 360 mm. Specimens examined by Vijayakumar & David (2006) had a mean SVL of 367.2 ± 42.0 mm). Ratio TaL / TL: 0.124–0.182 with a strong sexual dimorphism.

Body scalation. DSR 23–21—(19)21(23)—15 scales, rhomboid, smooth or usually weakly keeled; VEN 155–164, SC 46–72,all paired, with a sexual dimorphism; anal entire.

Only one specimen (ZSI 255547) has 19 DSR at midbody whereas 4 specimens out of 27 have 23 DSR.

Head scalation. As described for the lectotype, with rostral as high as wide or wider than high, more or less visible seen from above; 1 pair of enlarged, subrectangular internasals, 2 to 4 times as large as adjacent scales of upper snout surface, separated each from the other by 1 small scale in all examined specimens; 4 or 5 canthal scales bordering the canthus rostralis between internasal and corresponding supraocular, as large or barely larger than adjacent snout scales; on each side, 1 supraocular, rarely divided into two scales, elongated and narrow, about 2.7–3.2 times as long as wide, not much wider than adjacent upper head scales, 0.6–0.9 times as wide as internasals; scales on dorsal surface of head small, smooth, irregular in shape, larger on snout than in the frontal area; 9–11 cephalic scales in a line between supraoculars, small, very unequal, flat, subimbricated and smooth on top of the head, larger on the snout and posterior part of the head than between the eyes; scales on the occiput flat and smooth; temporals smooth; on each side 2–3 postoculars and 1 elongated, crescent-like subocular; 10–12 SL, rather large, 1st SL completely fused with nasal, 2nd SL tall, in contact with nasal and forming the anterior border of loreal pit or topped by a prefoveal scale bordering the pit (both conditions may occur in the same specimen), 3rd SL largest, elongate, about 1.1–1.3 times longer than high, in contact with subocular or rarely separated by 1 small scale, 4th SL lower than third one, separated from subocular by 1 or rarely 2 small scales, 5th and other posterior SL separated from subocular by 2 scales; 11–14 IL, first pair in contact with each other, 1st–3rd pairs in contact with anterior chin shields; 8–9 rows of smooth gular scales; chin shields regularly arranged.

Coloration and pattern. The colouration of this species is variable. There are two main morph of colouration and pattern, as follows:

(1) In the first morph (see Gumprecht et al. 2004: 222: Fig. I–IV, 223: Fig. I–III & 224: Fig. I-II; Vijayakumar & David 2006: 32: Fig. 20; Vogel 2006: 99: picture RS02581-4, 100: picture RS02583-4), the body is grey, greyish-brown, olive green or pale brown, with about 40 to 45 chesnut brown, dark brown or dark greyish-brown, black-edged dorsal blotches, 4–5 dorsal scales long and 4–8 scales wide, which do not extend far downwards on the sides; the blotches are often divided on the vertebral line on the anterior part of the body, with their halves more or less slightly set off each from the other; a longitudinal, discontinuous or rarely near solid brown stripe extend on 4th and 5th dorsal scale rows; it is edged on its both sides on 3rd and 6th dorsal scale rows respectively, by a series of greyish-brown or dark greyish-green scales that form a discontinuous stripe above and below the brown stripe; sometimes, this lateral stripe is entirely brown and divided into elongate, irregular lateral blotches; a pale longitudinal streak runs on neck sides; a discontinuous ventrolateral stripe, made of large, irregular, alternate, white spots and brown or reddish-brown spots, extends from the neck to the base of the tail on the outer tips of ventrals and first dorsal scale row. The tail is basically coloured and patterned as the body, with a faint crossbars anteriorly, vanishing after the first quarter of the tail which is entirely dark greyish-brown, reddish brown or rusty brown for the three posterior quarters.

Head dark brown or blackish-brown above and its sides, distinctly darker than the background colour of the body; sides of the snouts dark or slightly darker than upper head surface; supralabials blackish-brown or nearly black; a very well defined, narrow, white or cream streak extends on supralabials from the 1st supralabial to the lower margin of the eye, then, across lower temporals and upper margins of posterior supralabials, to the corner of the mouth, then reaches the ventrolateral stripe. Chin and throat are yellowish-brown or dark greyish-brown, strongly and finely speckled with both rusty brown or black dots, especially on the throat and the under surface of neck, and pale yellow dots. In life, iris brown, marbled with dark brown; black pupil.

The venter is yellowish-brown, greyish-brown, beige or dark brown, more or less strongly speckled with minute rusty brown and black dots, with or without white spots; tips of ventrals are brown or reddish-brown, much darker than their central part. The ventral part of the tail is dark rusty-brown, with dark brown spots, or uniformly dark brown.

(2) In the second morph (see Gumprecht et al. 2004: 224: Fig. IIII, 225: Fig. I–III & 226: Fig. I-III; Vijayakumar & David 2006: 30: Fig. 19; Vogel 2006: 99: picture RS02582-4, 100: pictures RS02584-4& RS02586-4), the body is dark yellowish- or reddish-brown, uniform or with faint dorsal blotches, barely darker than the background colour; sides paler and more red than upper dorsal surface, speckled with coral red spots, especially in the ventrolateral area; in some specimens, the red hue is replaced by pale brown; a narrow lateral, reddish- or yellowish-brown stripe, more or less distinct, extends on 1st and 2nd dorsal scale rows from neck to the base of the tail.

Head uniformly dark yellowish-brown or greyish-brown above, with some scattered minute dark dots; anterior supralabials ashy grey or greyish-brown, posterior supralabials reddish-brown; no temporal streak or a white, black-edged temporal streak, more or less distinct, extends from the eye to the corner of the mouth in some specimens; chin and throat yellowish-brown or greyish-brown, strongly and finely speckled with rusty brown and black, especially on the throat and the under surface of neck, infralabials coral red, throat with numerous coral spots or nearly entirely, although irregularly coral red. In life, iris brown, marbled with dark brown; black pupil.

The venter is beige, yellow or pale greyish-yellow, heavily speckled with minute coral red dots, especially posteriorly where the venter is nearly entirely coral red; tips of ventrals largely coral red. Ventral part of the tail nearly entirely coral red.

In preservative, the colouration changes into various shades of brown, greyish-brown and blackish brown, but pattern characters remain visible. Coral spots of morph II turn into brown or bluish-brown.

The lectotype designated above belongs to morph II.

Total Variance Explained Extraction Method: Principal Component Analysis.

Rotated Component Matrix

Component Extraction Method: Principal Component Analysis. Rotation Method: Varimax with Kaiser Normalization. Rotation converged in 5 iterations

Sexual dimorphism. There is a sexual dimorphism in (1) relative tail length: 0.174–0.182 (n=4) in males vs. 0.124–0.154 (n=8) in females; and (2) the number of subcaudals: 60–62 in males and 46–54 in females.

Stoliczka (1870b), on the basis of a dozen of specimens, thought that the differences in coloration and pattern described above were sex related. This is not the case according to our own material: 3 out of 4 males are banded, and 4 out of 22 females. The banded phase seems to be more common in males but can be found in both sexes.

Distribution ( Fig. 1 ). The species is endemic to the Nicobar Archipelago. It has been recorded from the islands of Bompoka, Camorta, Chowra, Katchal, Nancowry, Tarasa and Trinkat, all situated in the Central group. It seems to be absent from the Southern group and was not reported from Laouk and Tillangchong islands. Katchall Island in Central Nicobars is the southern boundary of its range, while Chowra Island forms its northern boundary.

Vogel (2006) depicted a specimen of this species with “Andaman Islands, India ” as locality. In fact the specimen shown on picture Nr RS02586-4 indeed originated from Trinket Island, Nicobar Islands (S. P. Vijayakumar, pers. comm., August 2013).

Figures

FIGURE 1. Map of the Andaman and Nicobar archipelago, (insert: Nicobar Islands showing: Car Nicobar Island (red), type locality of Trimeresurus labialis; Camorta Island, type locality, and distribution of Trimeresurus mutabilis (blue).

FIGURE 3. Trimeresurus mutabilis Stoliczka, 1870 from Chowra Island, Central Nicobars. Photograph by Manish Chandi.

FIGURE 4. Trimeresurus mutabilis Stoliczka, 1870 from Chowra Island, Central Nicobars. Photograph by Manish Chandi.

Tables

TABLE 2. Morphological characters of the syntypes of Trimeresurus labialis.

Collection number	NMW 18813:1	NMW 18813:2	NMW 18813:3
Sex	F	F	F
SVL (mm)	386	442	363
Tail-length (mm)	57	69	56
TaL/TL	0.129	0.135	0.134
Ventrals	171	168	171
Subcaudals	52	55	52
MSR	23	23	23
Cep	11	11	11
In sep	yes	yes	yes
Abbreviations.—See in Material and methods.