Hebius taronensis ( Smith, 1940 )

David, Patrick, Vogel, Gernot, Nguyen, Truong Quang, Orlov, Nikolai L., Pauwels, Olivier S. G., Teynié, Alexandre & Ziegler, Thomas, 2021, A revision of the dark-bellied, stream-dwelling snakes of the genus Hebius (Reptilia: Squamata: Natricidae) with the description of a new species from China, Vietnam and Thailand, Zootaxa 4911 (1), pp. 1-61 : 19-21

3. Hebius taronensis ( Smith, 1940)

( Figs. 6–7 )

Natrix venningi taronensis Smith, 1940: 482 .—

Type locality. “Pangnamdim”, now Pannandin , about 27°43’N, 97°52’E, Nawngmun Township, Putao District, Kachin State, Myanmar.— Holotype. BMNH 1946.1.13.55 (originally BM 1940.1.6.93), adult male; collected and deposited by Ronald Kaulback, 1937–1939 .

Natrix venningi taronensis .— Smith 1943: 286.

Amphiesma venningi taronensis .— Captain & Bhatt 2002: 354, 355; Welch 1988: 34; Zhao 2006: 175; Sharma 2007: 208.

Paranatrix venningi taronenis .— Mahendra 1984: 245.

Amphiesma taronense .— Das 2010: 335; Das 2012: 151; Wallach et al. 2014: 33 (in part: mention from Kachin State only).

Hebius taronensis .— Boundy 2020: 92; this work.

Specimens examined (14).— Myanmar. Kachin State. BMNH 1936.7.4.31, “Nam Ti Valley, Upper Burma”, now Ratnamhti (27°35’N, 97°47’E), north of the village of Alangdunhku, at about mid-distance between Langtao and Nawngmun, Putao District; BMNH 1946.13.55 (holotype), BMNH 1946.1.7.92–97, “Pangnamdin”, 27°42’N, 97°54’E, now Pannandin, Nawngmun Township, Putao District ; BMNH 1974.885–886, “Pangnamdin, 3000 ft, 27°42’N, 97°54’E ”, now Pannandin , Nawngmun Township ; BMNH 1946.1.13.44, “Aliwang, Taron Valley”, now Alawang (27°42’N, 98°08’E), near Renam , in the valley of the Nam Taron , Putao District ; CAS 221298, between Alonga and Ahtonga bridge, 27°16’51.3N, 97°45’31.8E, Machanbaw Township , Putao District ; CAS 224426–427: Pannandin Village , Hkakabo Razi National Park , Nawngmun Township , 27°43’28.7”N, 97°52’09.5”E, Putao District .

Taxonomic comments.—This taxon was described as a subspecies of Hebius venningi ( Wall, 1910) . Subsequently, it has rarely been cited as a valid taxon in the literature. It has even been overlooked, for example, by Dowling & Jenner (1988). However, Das (2010, 2012), Wallach et al. (2014) and Boundy (2020) recognized this taxon at full species level, although without justification. This species is monotypic.

On the basis of the differences in morphology between Natrix v. venningi and Natrix venningi taronensis discussed below and of their allopatric distribution, we consider them to be distinct at the specific level. This position has already been previously adopted in the list of snakes of Myanmar provided on the website of the California Academy of Sciences, by Das (2010: 335; 2012: 151) and by Wallach et al. (2014: 33); see the details above under the account of H. venningi . Following Guo et al. (2014), the species taronensis is placed in the genus Hebius .

Hebius taronensis may be confused with H. nigriventer , although the tail length and dorsal pattern in life are quite different. Our data show that these taxa differ by constant characters and should be considered distinct species; see above under the account of H. venningi . H. taronensis is now restricted to the north of Kachin State, in northern Myanmar and, tentatively, north-eastern India.

Diagnosis.—A moderately sized species of the genus Hebius characterized by the combination of (1) 17(18)- 17-17 dorsal scale rows, moderately keeled at midbody, strongly keeled posteriorly but 1 st DSR smooth; (2) dorsal scales around the base of the tail very strongly keeled; (3) head moderately distinct from the neck; (4) eye average; (5) maxillary teeth 28–32, the last two moderately enlarged; (6) tail moderately long, with a ratio TaL/TL <0.29; (7) VEN 158–176; (8) SC 92–104; (9) prefrontal scales 2; (10) 3 postoculars in all examined specimens; (11) anterior temporal more or less hexagonal, narrowing posteriorly; (12) venter both pale and dark, i.e., with a pale background on its anterior part, up to the third or half of the body, with the anterior half of each ventral typically brown or blackish-brown, producing a mottled pattern of irregular dark crossbands, sometimes reduced to one or two dark blotches on some ventrals; on its posterior part, the venter is nearly uniformly very dark ochre-brown, dark brown or blackish-brown; (13) dorsum and sides of body dark, i.e. brown, dark greyish-brown, dark brown and blackish-brown; (14) dorsal pattern made of faint, irregular pale blotches mixed with diffuse, squarish dark brown blotches forming a complex variegated or reticulate pattern, not distinctly chequered; (15) on each side, a series of small, elongate, dorsolateral blotches, pale yellowish-brown or ochre-brown (vividly colored in bright orange-yellow or bright yellow in life); (16) usually no clearly defined postocular streak; and (17) irregular yellowish-brown or yellow-ochre streaks or a faint blotch on the neck.

Comparison. Hebius taronensis differs from H. venningi by (1) a shorter tail, ratio TaL/TL 0.25–0.29 vs. 0.30–0.35 in H. venningi ; (2) fewer subcaudals, 92–104 vs. 115–129; (3) dorsum brown to blackish-brown with pale and dark spots or blotches forming a complex speckled or mottled pattern vs. dorsum grey or greyish-brown with a chequered pattern of darker blotches; (4) on each side, a series of more or less elongate blotches, pale yellowishbrown or ochre-brown (bright orange or yellowish-red in life) vs. yellow-ochre or yellowish-brown (same in life); (5) venter both pale and dark, i.e. with a pale background on its anterior part with the anterior half of each ventral brown or blackish-brown, producing a pattern of irregular dark crossbands, and venter nearly uniformly very dark ochre-brown, dark brown or blackish-brown on its posterior part vs. venter widely pale in its middle along at least the anterior part of the body, laterally clouded or dotted with dark grey or dark brown, never entirely dark.

The differences between H. taronensis and H. nigriventer have been given above in the diagnosis of the latter species.

Description.—Body rather slender, elongate, cylindrical, stouter in large females; head elongate, somewhat triangular, moderately distinct from the thick neck, flattened anteriorly; snout elongate, obtuse as seen from above, oblique seen in profile, flat, 24.5–30.5 % of HL, or 1.8–2.1 times as long as diameter of eye; nostrils placed dorsolaterally on the snout, small, round, piercing in the middle of the nasal; eye size average, about 1.0–1.2 times as large as the distance between its lower margin and the margin of the lip, with a round pupil; tail rather long and tapering.

The maximal known total length is 833 mm (SVL 581 mm; TaL 252 mm; specimen CAS 224427) for a female. The longest known male is 634 mm long (SVL 458 mm, TaL 176 mm long; BMNH 1946.1.13.55).

Ratio TaL/TL: 0.254 –0.288, without sexual dimorphism (see below).

Dentition. 27–32 maxillary teeth gradually enlarging, the last 2 moderately enlarged, without diastema.

Body scalation. DSR: 17(18)-17-16–17 rows; scales rhomboedric, feebly or moderately keeled at midbody, strongly keeled posteriorly; scales of 1 st DSR smooth; dorsal scales around the base of the tail very strongly keeled.

In our sample of 12 specimens, only one has 18 scale rows around the neck.

VEN: 158–175 (plus 1 or 2 preventrals); SC: 92–104, all paired; cloacal plate divided.

Ratio VEN/SC 1.66–2.02.

Position of the reduction to 6 scale rows around the tail: SC 9–14, without sexual dimorphism; ratio: length of the portion of tail with 6 dorsal scale rows/length of the portion of tail with 4 dorsal scale rows: 1.3–3.1.

Head scalation. Arrangement of upper head scales complete including 2 internasals, 2 prefrontals, 2 supraoculars, 1 frontal, and 2 parietals. Rostral wider than high, barely visible from above; nasals more or less rectangular, elongate, about 1.4–1.6 times longer than high, vertically divided above and below the nostril, with the posterior part equal to anterior one; internasals subtriangular, small, in broad contact with each other, about 1.0–1.2 times longer than wide, distinctly narrowing anteriorly with an anterior margin about 0.4–0.5 times the width of the posterior margin; 2 prefrontals, rather large, distinctly wider than long, 1.2–1.3 times longer than internasals; frontal large, shield-like, 1.2–1.3 times longer than wide and 1.6–1.9 times as long as the prefrontal; 1 supraocular on each side, subtriangular, 2.0–2.3 times longer than wide, about as wide as internasals; parietals large and broad, 1.6–1.8 times longer than the frontal, or suture between parietals 1.1–1.3 times longer than frontal; 1/1 loreal, pentagonal, elongate, 1.4–1.5 times longer than high, in broad contact with the nasal; 2 preoculars on each side in all examined specimens, upper one larger than lower one; 3/3 small postoculars in all examined specimens; 9 SL (only 8 SL in 1/18 occurrences), the first five as long as high or longer than high, 1 st and 2 nd SL small and short, in contact with the nasal, 2 nd– 3 rd SL (3 rd– 4 th in one specimen) in contact with the loreal in all examined specimens, 4 th– 6 th SL entering orbit, 7 th and 8 th SL largest; 1 anterior temporal, long, hexagonal, distinctly narrowing posteriorly, followed by 1 or 1+1/1 posterior temporals, the most common formula being 1+1 temporals; 10 infralabials in all examined specimens, first pair in contact, 1 st– 5 th IL in contact with anterior chin shields, 5 th and 6 th IL largest; posterior chin shields longer than anterior ones.

Coloration and pattern. The upper dorsal surface is dark ochre-brown, chestnut brown or dark brown, sometimes blackish-brown, with many scales irregularly edged or entirely covered with dark brown or blackish-brown, especially on the top of the body, mixed with irregular, diffuse, faint paler areas, pale yellowish-brown or pale brown, producing a complex, irregularly marbled or reticulate pattern; on each side of the body, a dorsolateral series of distinctly enlarged, aligned, pale creamish-brown or pale ochre-brown blotches, about 1.5–2 scales long and 2–3 scales high on the 4 th– 6 th or 5 th– 6 th DSR, forming a discontinuous dorsolateral chain; these blotches become quickly reduced in size, remaining as very faint pale spots in the hinder part of the body and are poorly visible posteriorly, mixed in the general dorsal pattern. The dorsal surface of the tail is as the upper surface of the body, irregularly mottled with many darker blotches but without distinct pale areas.

The head is dark brown or blackish-brown above, darker than the sides of body, irregularly mottled with paler areas and speckled with darker dots or with irregular darker brown areas; side of the snout slightly paler than upper head surface; anterior or all supralabials pale brownish-yellow, pale or brown, strongly powdered and more or less broadly edged with dark brown on their posterior edge; usually no real dark postocular streak, the temporal region being merely mottled with irregular paler brown; however, in a few specimens (such as CAS 221298), a pale yellowish-brown elongate blotch on the temporal region defines a lower, broad, dark brown streak, connecting posterior temporals to the corner of the mouth; on each side of the neck an irregular, more or less well-defined, yellow-ochre or brownish-yellow streak obliquely directed upwards and backwards extends from the corner of the mouth to the nape forming a short chevron with an apex directed backwards, faint or absent in darker specimens; infralabials, chin and throat pale yellowish-cream or pale yellow-ochre, with a few scattered dark brown spots on chin shields and throat, sometimes heavily spotted with dark brown; infralabials strongly edged with dark brown on their both edges, and often strongly speckled with dark brown.

The venter is both pale and dark: the background colour is beige, pale greyish-brown or pale ochre-brown on its anterior part, i.e., along the anterior quarter to third, sometimes up to nearly the half of the body, and dark brown or blackish-brown on its posterior part; the first 10–15 ventrals may be merely speckled with brown blotches but, typically, the anterior half of each ventral is irregularly covered with dark brown or blackish-brown, producing a pattern of irregularly-edged, dark crossbands on a paler background; backwards, the dark area progressively expands up to covering the whole of each ventral, often so irregularly as to leave one or two blotches of pale area on the middle of ventrals; after midbody the venter is uniformly dark up to the vent, with the posterior margin of each ventral paler brown; no ventral or ventrolateral pale stripes or streaks. Tail uniformly dark brown or blackish-brown below; tip of tail as the undersurface of tail.

In life, the pattern is much more vivid and contrasted; the background coloration is as described above, usually dark brown or nearly black; the faint, dorsal paler areas are dark ochre-brown or yellowish-brown; dorsolateral blotches are vividly colored in bright lemon-yellow, orange-yellow or yellowish-red, visible throughout the length of the body. Pale markings on the head, the supralabials, the elongate blotch on the temporal region and the streak obliquely directed upwards and backwards on the hinder part of the head and the neck are dirty yellow or yellowish-ochre. Pale areas of the venter are yellowish-ochre or yellowish-brown.

Hemipenes.—The hemipenis of this species has not been examined.

Sexual dimorphism. — It is expressed in the two following characters:

(1) Difference in the number of ventral scales: males: 171–175 (mean = 172.6, SD = 1.5); females: 158–171 (mean = 165.6, SD = 1.5).

(2) Strongly by the ratio length of the portion of tail with 6 dorsal scale rows/length of the portion of tail with 4 dorsal scale rows: 2.6–3.1 in 4 males, 1.3–2.0 in 2 females.

Distribution ( Fig. 3 ).— Myanmar. Kachin State. Lake Indawgyi, Mohnyin Township; Nawgmung Township and Machanbaw Township, Putao District.— India. State of Arunachal Pradesh. Changlang District.

In Myanmar, this species is currently endemic to the mountain ranges located north-east of Putao and Mawgmung, in the extreme north of the country. Farther south in the same state, it is replaced by Hebius nigriventer .

The presence of H. taronensis in extreme north-eastern India is based on a specimen cited by Captain & Bhatt (2002). Although we have not seen it, its number of subcaudals and relatively short tail are typical of H. taronensis . We here add this species to the snake fauna of India.

Biology.—This species inhabits semi-evergreen submontane forest and mixed or deciduous moist montane forest from about 1,000 up to at least 1,850 m asl. Most known localities are between 1,100 and 1,800 metres a.s.l. H. taronensis is seemingly diurnal. According to Smith (1940), most specimens were obtained from small mountain streams. One was eating a frog, another specimen had eaten tadpoles. Others were found under rocks near a stream. Nothing else is known on the biology of this seemingly rare or highly localized species. According to Smith (1940), this water snake is quiet and harmless.

Figures

FIGURE 3. Distribution map of species with 15 or 17 dorsal scale rows at midbody. Circles: Hebius annamensis Bourret. Diamonds: Hebius venningi Wall. Inverted triangles: Hebius taronensis Smith. Squares: Hebius nigriventer Wall. Triangles: Hebius chapaensis Bourret.

FIGURE 6. Hebius taronensis Smith, holotype (BMNH 1946.1.13.55)—A: dorsal view; B: ventral view; C: lateral view of the head, right side; D: close-up dorsal view of the head. Photographs: Gernot Vogel.

FIGURE 7. Hebius taronensis Smith, alive—Specimen from Lake Indawgyi, Mohnyin Township, Kachin State, Myanmar. Photograph: Nikolay Poyarkov.