Hebius nigriventer (Wall, 1925) David & Vogel & Nguyen & Orlov & Pauwels & Teynié & Ziegler, 2021

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 : 13-19

2. Hebius nigriventer (Wall, 1925) new comb.

( Figs. 4–5 )

Natrix nigriventer Wall, 1925a: 588 .—

Type locality. “Huton, Bhamo District (30 miles north-east of Bhamo; circa 4,500 feet; Lat. circa 97°33; Long. Circa 24°24”, now Hutung , Bhamo District, Kachin State, Myanmar.— Holotype. BMNH 1946.1.13.60 , adult female; collected by Father Gilhodes, June 1924.

Natrix nigriventer .— Bourret 1936b: 55 (synonymy with Natrix venningi ).

Hebius nigriventer .—This work.

Natrix venningi (nec Tropidonotus venningi Wall, 1910 ).— Wall 1926: 560 (in part); Bourret 1936b: 55 (in part: only the mention of “ Chine ”); Smith 1943: 286 (in part).

Tropidonotus venningi (nec Tropidonotus venningi Wall, 1910 ).— Werner 1929: 24 (in part).

Amphiesma venningi (nec Tropidonotus venningi Wall, 1910 ).— Kou 1985: 160 (in part); Zhao & Jiang 1986: 239 (?; identification uncertain); Zhao & Adler 1993: 228 (in part), 310; Zhao et al. 1998: 89 & 90 (in part); Zhang 1999: 430 (?); Zhao et al. 2000b: 205; Iskandar & Colijn 2001: 98 (mention from China); He & Zhou 2002: 167 (in part); Ji 2002: 184; Zhao 2006: (Vol. I) 174 (in part), (Vol. II) 97: Fig. 59-2–59-3 (Fig. 59-1 depicts a Hebius bitaeniatus ); David et al. 2007: 54 (in part), 55 & 60 (in part: three specimens from Kachin State, Myanmar); Sharma 2007: 207 (in part); Yang & Rao 2008: 268 (text: in part; Figure: H. nigriventer ), 269 (text: in part, Table 58: H. nigriventer ); Luo et al. 2010: 74; Zhang 2011: 277 (?); Wallach et al. 2014: 33 (in part: only mentions from Kachin State, Myanmar, and Yunnan, China).

Amphiesma Venrrinig [sic]).— Kou & Zhang 1987: 364.

Specimens examined (14).— Myanmar. Kachin State. BMNH 1925.9.17.6, BMNH 1925.12.22.21, BMNH 1946.1.13.60 (holotype of Natrix nigriventer ), Huton, now Hutung, Kachin Hills, Bhamo District; CAS 238901– 902, vicinity of Nanmon Village , Indawgyi Lake Wildlife Sanctuary , Moenyin Township , Myitkyina District , 24°57’35”N, 96°20’36”E; CAS 245436, north side of Panwa Town , 25°36’54.1N, 98°22’31.5E, Panwa Township , Myitkyina District , 7,147 ft. — People’s Republic of China. Yunnan Province. CAS 241960, Kongdang township in Dulong Valley , along road from hotel (Kongdang) to bridge approx. 3 km N of hotel (Kongdang), 27°54’03.6”N, 98°20’52.0”E, Gongshan County, Nujiang Prefecture ; CIB 8278, Jinhong Prefecture ; KFBG 14536, Hongbenghe , Xueli Village , Yingjiang County , Dehong Dai and Jingpo Autonomous Prefecture ; YU 844023, YU 845075–076, Mengla, Mengla County , Jinhong Prefecture. YU 835043–044, Jinhong, Jinhong Prefecture .

Taxonomic comments.—This taxon was described as a valid species by Wall (1925a) but subsequently synonymized with Natrix venningi by Wall (1926: 560), a position accepted by Smith (1943). However, Wall (1926) put emphasis on the similarities in the numbers of dorsals and maxillary teeth between the two taxa but, with three specimens at hand from Hutung, Kachin State, failed to notice the strong differences in their dorsal pattern. On the basis of important and constant differences in the pattern and the other morphological characters detailed below, we resurrect Natrix nigriventer from the synonymy of Natrix venningi Wall, 1910 and consider it to be a valid species under the combination Hebius nigriventer new comb. This species is monotypic.

H. nigriventer is undoubtedly related to Hebius venningi , and constitutes the “north-eastern” member in the informal H. venningi complex. It also occurs near the distributional range of H. taronensis . These species can be differentiated by the characters given above in the introduction to the informal groups, and by the diagnosis given below in the account of H. nigriventer . Nevertheless, H. taronensis and H. nigriventer seem to be closely related.

It should also be noted that H. nigriventer is quite similar to H. chapaensis . Variation in this latter taxon are still imperfectly known, especially the ratio tail length/total length and the number of subcaudals on which is mostly based the difference between these two species. The values of these characters may be expended when more specimens are available. Furthermore, H. chapaensis is highly variable in both dorsal and ventral colour pattern. Lastly, H. chapaensis also occurs in Jinhong Prefecture, Yunnan Province (Jinlong Ren, pers. comm., June 2020), just as does H. nigriventer . Nevertheless, our data suggest that these taxa are indeed distinct at species level.

According to Jinlong Ren (pers. comm., June 2020), the presence of H. nigriventer in both western Yunnan and Myanmar on the one hand, and southern Yunnan on the other hand, isolated areas with very different herpetofaunas, may suggest that H. nigriventer is a species complex.

Hebius nigriventer has constantly been cited in the Chinese literature under the combination Amphiesma venningi , for example by Kou (1985), Kou & Zhang (1987; as Amphiesma Venrrinig [sic]), Zhao et al. (1998), Zhao (2006) and Yang & Rao (2008).

Diagnosis.—A moderately sized species of the genus Hebius characterized by the combination of (1) 17(exceptionally 19)-17-15–17 dorsal scale rows, moderately keeled at midbody, strongly keeled posteriorly but 1 st DSR smooth; (2) dorsal scales around the base of the tail strongly keeled; (3) head moderately distinct from the neck; (4) eye size moderate; (5) maxillary teeth 28–33, the last two moderately enlarged; (6) tail long, with a ratio TaL/TL at least equal to 0.29 in females, up to 0.37 in males; (7) VEN 155–168; (8) SC 105–143; (9) 2 prefrontal scales, (10) anterior temporal elongate, rectangular; (11) venter entirely very dark, i.e., blackish–brown or black, sometimes with two, narrow longitudinal paler stripes, at the exception of a middle stripe pale but heavily blotched with dark hues anteriorly, extending on 5–15 ventrals; (12) dorsal colour very dark, dark brown, very dark greyish-brown or blackish-brown; (13) dorsum background either uniform or with a subdued chequered dorsal pattern made of large, diffuse, rectangular darker blotches on 4 th– 5 th and 7 th– 8 th DSR; (14) on each side, a series of large, cream or pale yellowish-brown (bright orange, rusty-red or reddish-brown in life), rectangular blotches, higher than long anteriorly then more elongate, forming a conspicuous, dorsolateral chain of blotches on 5 th– 6 th DSR throughout the length of the body, becoming smaller posteriorly and turning to an irregular stripe posteriorly; (15) a dark postocular streak usually present; and (16) a short, oblique yellowish-brown or yellow-ochre streak (bright orange or rusty-red in life) above the corner of the mouth and a large blotch of the same colour on the side of the neck.

Comparison. Hebius nigriventer differs from H. taronensis , with which it might be sympatric in northern Myanmar (Kachin State) by (1) the dorsal general colour and pattern, i.e, a very dark background colour with a uniform or weakly and partly chequered pattern vs. a dark background with pale and dark spots or blotches forming a complex speckled or mottled pattern in H. taronensis ; (2) a conspicuous dorsolateral chain or stripe of bright, orange or rusty-brown blotches vs. a series of small pale yellowish-brown or ochre-brown dorsolateral blotches on the anterior part of the body; (3) venter nearly entirely very dark, i.e. blackish-brown or black, vs. 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; (4) a longer tail, ratio TaL/TL 0.29–0.37 vs. 0.25–0.29 in H. taronensis , especially in males: 0.32–0.37 vs. 0.25–0.29; (5) more subcaudals, 105–143 vs. 92–104 SC; (6) fewer ventrals in males, 156–168 vs. 171–175 VEN; (7) a difference in the ratio VEN/SC: 1.16–1.59 vs. 1.66–2.02; and (8) the number of postoculars, usually 2, rarely 3 in H. nigriventer vs. always 3 in H. taronensis .

H. nigriventer differs from H. venningi , by (1) the dorsal general colour and pattern: a very dark background colour vs. dorsum grey, greyish-brown or, more rarely dark brown, with a distinct chequered pattern of darker blotches in H. venningi ; (2) a conspicuous dorsolateral chain or stripe of bright, orange or rusty-brown blotches vs. a dorsolateral series of irregular blotches, yellow-ochre or yellowish-brown (bright yellow-ochre in life), enlarged and forming a chain on the first quarter to third of the body, usually vanishing after midbody in H. venningi ; (3) venter entirely very dark, blackish-brown or black, sometimes with two, narrow longitudinal paler stripes vs. venter widely pale in its middle part along at least the anterior part of the body, laterally clouded or dotted with dark grey or dark brown, never entirely dark; (4) the position of the reduction to 6 scale rows around the tail in males: SC 9–14 vs. SC 19–24; and (5) the number of postoculars, 2, rarely 3, vs. always 3 in H. venningi .

The list of these characters may not clearly express the visual differences between H. nigriventer , an overally dark species with highly contrasted bright orange dorsolateral blotches, and H. venningi , a usually paler species, more “grey”, with a much more subdued chequered dorsal pattern. It should be noted that specimen CAS 233206 has a very dark brown background dorsal colour and a venter pale only along the first 10–15 ventrals. However, the dorsal chequered pattern and the lack of the conspicuous dorsolateral bright orange or rusty-brown blotches make it undoubtedly referable to H. venningi .

Lastly, H. nigriventer is morphologically quite similar to H chapaensis . Differences between these two species are given below in the account of H. chapaensis .

Description.—Body rather slender, elongate, cylindrical, stouter in large females; head elongate, triangular, moderately distinct from the thick neck, flattened anteriorly; snout elongate, obtuse as seen from above, oblique seen in profile, flat, amounting for 27.5–31.5 % of HL, or 1.9–2.1 times as long as diameter of eye; nostrils placed dorsolaterally on the snout and directed dorsolaterally, small, round, piercing in the middle of the nasal; eye average, about 1.0–1.1 times as large as the distance between its lower margin and the margin of the lip, with a round pupil; tail long and tapering.

The maximal known total length is 716 mm (SVL 458 mm; TaL 258 mm; specimen CAS 241960) for a male. The longest known female is 593 mm long (SVL 391 mm, TaL 202 mm long; KFBG 14536). However, specimen CAS 238901, with an incomplete tail, has a SVL of 454 mm.

Ratio TaL/TL: 0.291 –0.366, with a weak sexual dimorphism (see below).

Dentition. 28–32 maxillary teeth gradually enlarging, the last 2 moderately enlarged, without diastema.

Body scalation. DSR: 17(19)-17-15–17 rows; scales rhomboedric, moderately keeled at midbody, more strongly keeled posteriorly; scales of 1 st DSR smooth; scales around the base of the tail very strongly keeled.

In our sample of 13 specimens, only one specimen has 19 scale rows around the neck. Two others have 16 scale rows before vent, two have 15 rows.

VEN: 155–168 (plus 1 or 2 preventrals); SC: 105–143, all paired, with a weak sexual dimorphism (see below); cloacal plate divided.

Ratio VEN/SC 1.16–1.59, with a weak sexual dimorphism (see below).

Position of the reduction to 6 scale rows around the tail: SC 7–14, with a distinct 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: 2.1–3.1.

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 1.5–1.8 times longer than high, vertically divided above and below the nostril, with the posterior part equal to anterior one; internasals rather small, trapezoid, in broad contact with each other, about 1.1–1.2 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 small, short, wide, wider than long, 0.9–1.1 times as long as internasals; frontal large, shield-like, 1.1–1.3 times longer than wide and 1.8–2.1 times as long as the prefrontal; 1 supraocular on each side, subtriangular, 2.0–2.2 times longer than wide, about as wide as internasals; parietals large and broad, 1.5–1.6 times longer than the frontal, or suture between parietals 1.0–1.1 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; 2 (in 8/24 occurrences) or 3 (16/24 occurrences) small postoculars; 9/9 SL in all examined specimens, 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 or more rarely 2 nd– 4 th, 3 rd or 3 rd– 4 th SL in contact with the loreal, 4 th– 6 th (5 th– 6 th in two specimens) SL entering orbit, 7 th and 8 th SL largest; 1 anterior temporal, elongate, rectangular, followed by 1 or, rarely 1+1/1 or 2 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 brown or blackish-brown, either nearly uniform or with, on each side, two series of subdued, poorly visible large, rectangular darker blotches, about 2–2.5 scales long and wide, one on the top of the back on the 7 th– 8 th DSR, the other series on the 3 rd– 4 th or 4 th– 5 th DSR forming altogether a diffuse chequered pattern; on each side throughout the length of the body, a dorsolateral series of conspicuous distinctly enlarged, vertically elongate or triangular blotches, pale creamish-brown or pale ochre-brown in preservative (see below in life), extending on the 4 th– 6 th or 5 th– 6 th DSR, longitudinally separated by 2 or 3 dorsal scales, about 1.5–2 scales long and 2–3 scales high anteriorly; after midbody, these conspicuous blotches become smaller and squarish or irregularly-shaped, then elongate posteriorly and forming a discontinuous dorsolateral chain or an irregular stripe; some small orange spots or blotches on the bottom of the sides. The tail is as dark as the upper surface of the body, possibly mottled with irregular darker blotches; a dorsolateral series of orange-brown, rusty-red or brownish-red elongate spots or dashes up to the tip of the tail.

The head is dark brown or blackish-brown, irregularly mottled above with both paler and darker brown vermiculations or diffuse areas; loreal and nasal either dark brown or with a paler area, pale yellowish-brown spotted with dark brown; 1 st– 6 th or 1 st– 7 th supralabials dirty creamish-yellow or pale yellowish-brown, 1 st– 3 rd SL usually strongly speckled with dark brown, all broadly edged with dark brown or blackish-brown on their posterior edge, sometimes the pale coloration being restricted to the forward half of the suparalabial; last supralabial with a large pale blotch on its upper part, pale creamish-yellow or creamish-brown; a broad, dark postocular streak extending obliquely from postoculars to the two upper parts of posterior supralabials and to the corner of the mouth; a narrower, oblique streak or a series of small, elongate blotches, dirty creamish-yellow or pale yellowish-brown, extending above the dark streak from the upper postocular to the large pale blotch on the 9 th SL and to behind the corner of the mouth; on each side of the neck, an irregular, rather broad streak, pale creamish-yellow or yellowish-brown (see below in life), obliquely directed upwards and backwards, extends from behind the corner of the mouth to the nape, forming a short chevron with an apex directed backwards. Infralabials, chin and throat yellowish-cream or pale yellow-ochre, with scattered dark brown spots on chin shields and throat, sometimes heavily spotted with dark brown; infralabials strongly edged with dark brown on both anterior and posterior edges, and often strongly speckled with dark brown, being sometimes more brown than pale.

The venter is dark brown, blackish-brown or black on nearly its whole length at the exception of first 10–20 ventrals, pale in their middle but heavily blotched with dark hues; often, three narrow longitudinal stripes, paler brown or yellow-ochre, one in the middle of the venter, the other ones on the outer third of each ventral along the anterior half of the body after the pale central area, vanishing at the level of third to half of the body, making the venter nearly uniformly dark on its posterior part; tips of ventrals without dark blotch but with a streak of the pale colour forming an irregular ventrolateral stripe reduced to the anterior part of the body. Tail uniformly dark brown or blackish-brown below; tip of tail very dark.

In life, the overall coloration is as described above but more constrasted; the dorsal surface is dark or nearly black, somewhat shining; large and small, elongate dorsolateral blotches are conspicuous, bright orange-brown, redochre, rusty-red or brownish-red, strongly constrasting with dark background colour. Pale markings on the head and supralabials are dark greenish-yellow, yellowish-ochre or pale yellowish-brown; the narrow, arched streak, or the series of irregular blotches extending from the upper postocular to the 9 th SL and to behind the corner of the mouth are yellow-ochre, pale yellowish-brown, orange brown or rusty red; the broad streak on each side of the neck has the same colour than dorsolateral blotches. Pale areas of the venter are yellowish ochre or brownish-yellow, never in reddish hues.

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

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

(1) strongly by the difference in the ratio TaL/TL: males: 0.348 –0.375 (mean = 0.353, SD = 0.019); females: 0.291 –0.341 (mean = 0.312, SD = 0.026).

(2) by the difference in the number of subcaudals: males: 124–143 (x= 133.0, s = 7.5); females: 105–126 (mean = 112.0, SD = 9.7).

(3) Strongly by the difference in the position (counted in subcaudals) of the reduction of scale rows around the tail to 6: males: SC 9–14; females: SC 6–7.

Distribution ( Fig. 3 ).— Myanmar. Kachin State. Bhamo District; Myitkyina District.— People’s Republic of China. Yunnan Province. Yingjiang County, Dehong Dai and Jingpo Autonomous Prefecture; Gongshan County, Nujiang Prefecture; Mengla County, Jinhong Prefecture.

This species may also be present in northern Laos.

Biology.—This species inhabits evergreen or semi-evergreen submontane forest and mixed or deciduous moist montane forest from 350 up to 1,550 m asl. According to data relative to a few specimens, H. nigriventer is both diurnal and active at dusk or in the early part of the night, at air temperatures from about 24 to 27 °C. This species is seemingly largely aquatic. Most snakes were found in hill or montane streams, between or on rocks in the stream bed. One of the specimens mentioned by Wall (1925) had swallowed two large and four small tadpoles. Another one, a female collected in June, contained two large eggs, indicating that egg laying would have taken place at the beginning of the rainy season.

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 4. Hebius nigriventer Wall, holotype (BMNH 1946.1.13.60)—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 5. Hebius nigriventer Wall, alive—A & B: specimen KFBG 14536, Xueli, Yingjiang County, Yunnan Province, China. Photograph: Jian-Huan Yang.