Hebius modestus (Günther, 1875)

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 : 35-40

6. Hebius modestus (Günther, 1875)

( Fig. 13 )

Tropidonotus modestus G̹nther, 1875: 232.—

Type locality. “The Himalayas”, specified as being the “ Khasi Hills ”, State of Meghalaya, India, according to Boulenger (1893a: 229) and the BMNH’s collection catalogue.— Syntypes. BMNH 1946.1.13.40 and BMNH 1946.1.13.41, two adult males; collected by Dr. Thomas C. Jerdon.

Tropidonotus modestus .— Anderson 1879: 817; Theobald 1882: 302; Boulenger 1890: 343; Sclater 1891: 36; Boulenger 1893a: 229; Boulenger 1893b: 308 & 322; Werner 1929: 15 & 25.

Nerodia modesta .— Wall 1923: 603; Wall 1925b: 809; Wall 1926: 560.

Natrix modesta .— Mell 1929: 5, 16, 145 (in part: mention from “Osthimalaya” only), 147 (in part: mention from “Osthimalaya” only) & 157; Mell 1931a: 203 (species with 19 DSR), 1931b: 231; Pope 1935: 90 (discussion about the species cited by Anderson 1879); Bourret 1936a (in part): 94, 103 (only mentions from “Assam & Bengale” and “Yunnan”; the mention given on p. 113 refers to Hebius boulengeri ); Bourret 1936b: 72 & 73 (in part; mentions from Assam and Yunnan); Smith 1943: 290–291 (in part, except specimens from “Upper Laos ”, “ Cambodia ”, “South Annam [Langbian Plateau]”, and “Pen[insular] Siam ”); Deuve 1970: 84 & 88 (in part: except specimens from “Xieng Khoang”); Anonymous 1977: 62; Hu et al. 1980: Pl. 38, 11 (in part) & 70 (in part); Yang et al. 1983: 43 (in part).

Natrix modista [sic].— Yang et al. 1978: 67 (in part).

Amphiesma modesta .— Malnate 1960: 50, 52 & 57; Whitaker 1978: 117; Murthy 1986: 72; Tian et al. 1986: 116 & 149; Yang & Inger 1986: 7; Zhao & Jiang 1986: 239; Welch 1988: 31 (in part: except mentions from Laos, Vietnam and Cambodia); Murthy 1990: 72; Zhao & Adler 1993: 227 (in part: only mentions of Yunnan, India and northern Burma) & 310 (in part: Yunnan); Mathew 1995: 437 & 438 (in part: except mentions from Thailand, Cambodia, and Laos); Das 1996: 53; Nguyen & Ho 1996: 69 (in part: not the specimens from Vietnam and localities herein); Zhao & Yang 1997: 205 (in part), 206: Fig. 62; Cox et al. 1998: 45 (in part: only the mention from Assam, the figure depicts a Hebius khasiensis ); Mathew 1998: 132; Sharma 1998: 94; Zhao et al. 1998: 51 & 65 (in part), 66: Fig. 19; Zhang 1999: 430 (in part); Orlov et al. 2000: 71 (in part, only the mentions of south-western China, Myanmar and India); Iskandar & Colijn 2001: 96 (in part: except mentions from Cambodia, Laos and Vietnam); Das 2002: 18 (text: in part, except mentions of Thailand, Laos and Vietnam; figure: Hebius khasiensis ); Hallermann et al. 2002: 150; He & Zhou 2002: 167 (in part); Ji 2002: 178 & 179; Sharma 2003: 132 & 133; Stotz et al. 2003: 100; Borang et al. 2005: 22; Sanyal & Gayen 2006: 271 (in part) & 283; Sharma 2007: 209 (in part: except mentions from Thailand, Cambodia, Laos and “ Annam ”); Yang & Rao 2008: 259 (in part); Luo et al. 2010: 74 (in part); Murthy 2010: 33; Zhang 2011: 277 (in part); Guo et al. 2014: 431.

Amphiesma modestum . — Zhao et al. 2000b: 205; Das 2003: 473; David et al. 2005: 175; Whitaker 2006: 112; Zhao 2006: (Vol. I) 167 (in part; only for mentions from Yunnan; the status of the specimen depicted in Vol. II: p. 89: Fig. 51 is addressed below in the Discussion); Zhang 2009: 82 (in part: Fig. 81 does not depict this species); David et al. 2007: 41, 42, 54, 56, 57 & 59; Das 2010: 333 (in part: except mentions of northern Laos, south-central Cambodia and central Vietnam); Bain & Hurley 2011: 104 & 128 (in part); David et al. 2013: 302, 308, 310, 312: Fig. 4C , 314, 324, 325, 326 & 335.

Amphiesma modestus . — Guo et al. 2014: 432.

Hebius modesta .— Guo et al. 2014: 428 (specimen CAS 234262).

Hebius modestum .— Guo et al. 2014: 437 & 438.

Hebius modestus .— Boundy 2020: 92; Wang et al. 2020, Appendix 2: 15; this work (see below in the Discussion).

Natrix modesta modesta . — Bourret 1936b: 73 (in part: mentions from Assam and Yunnan; Fig. 30 on p. 74 refers to another species; see below).

Specimens examined (14).— India. State of Meghalaya. BMNH 76.2.16.1–2, “Cherra Punji, Khasi Hills”, now Cherrapunji; BMNH 1946.1.13.40–41 (syntypes), Khasi Hills ; ZSI 4276, “Cherrapunji, Assam ”; ZSI 15263, “ Assam ”, no specified locality .— Myanmar. Kachin State. BMNH 1925.4.2.16, “ Hutong, Bhamo District ”, now Hutung; BMNH 1925.9.17.2, BMNH 1925.12.22.22–23, “Huton, Kachin Hills”, now Hutung, Kachin Hills, Bhamo District . Shan State. MNHN 1893.0400, “Mts Carin, 1200–1300 m ”, now Mts. Karen, locality specified by Boulenger (1893b: 322) as “Thao, District of Karin Bia-po”, now Tahò, 19°23’N, 96°54’E, Tauggyi District in extreme south-western Shan State. — People’s Republic of China. Yunnan Province. CAS 234262, Fangma Qiao River, 15–16 km from Longshan (Longling County, Baoshan Prefecture ), 24°32’38.1”N, 98°38’49.2”E, Mangshi County , Dehong Dai and Jingpo Autonomous Prefecture , 1,140 m a.s.l.; CIB 81II0366 ( Nr 8275), Baoshan , Baoshan Prefecture ; KIZ 75II0238, Tongbiguan , Yingjiang County , Dehong Dai and Jingpo Autonomous Prefecture .

Taxonomic comments.—This species was described on the basis of two specimens, as clearly stated by G̹nther (1875) in the original description. Boulenger (1893a: 229) also recognized two types. Wallach et al. (2014: 30) stated that Nguyen et al. (2009: 356) had designated specimen BMNH 1946.1.13.41 as the lectotype of the species. We consider this assertion to be erroneous as Nguyen et al. (2009: 356) only stated that this specimen was the “type”; this brief mention contravenes Art. 74.7 of the Code and cannot be construed as the valid designation of a lectotype.

The chresonymy given above includes only those citations dealing with Hebius modestus as currently conceived, although some refer to this species only in part. Tropidonotus modestus G̹nther, 1875 has been one of the most confused species in the genera Natrix and Amphiesma . Whereas Anderson (1879; genuine specimens from Yunnan) and Boulenger (1890, 1893a) correctly described the species as conceived here, the confusion arose from Smith (1943: 290) who adopted a large, and quite erroneous, definition of Natrix modesta and included under this name no less than four currently valid species, i.e., Hebius modestus , H. deschauenseei (Taylor) , H. groundwateri (Smith) and H. inas (Laidlaw) . Hebius boulengeri Gressitt, 1937 was not explicitly cited as a synonym by Smith (1943) but has been confused by this latter author and, more widely subsequently in the literature with Hebius modestus for populations of Laos, Cambodia and Vietnam. The chresonymy of H. boulengeri can be found in David et al. (2013), with a list of the numerous citations of Amphiesma modestum or Natrix modesta referring to Hebius boulengeri . As shown by David et al. (2013), most records of Hebius modestus from southern China and Vietnam, and all those from Cambodia and Laos should refer to Hebius boulengeri (for example, in Mell 1922; Angel 1929; Smith 1943 [see above in the chresonymy]; Campden-Main 1970; Deuve 1970; Saint Girons 1972 [in part]; Zhao & Adler 1993; Nguyen et al. 1995, 2009; Daltry & Chheang 2000; Grismer et al. 2007, 2008; Das 2010 [in part; see above in the chresonymy]; and Daltry & Traeholt 2003; list not exhaustive; see David et al. 2013 for a more complete list). However, David et al. (2013) erroneously considered citations by Mell (1929: 5, 16, 145 [in part], 147 [in part] & 157) to belong to the chresonymy of Hebius boulengeri . In fact, as Mell mentioned specimens from “Osthimalaya” (i. e. Eastern Himalaya), he most likely made reference to Hebius modestus or, perhaps to the new species described below. Furthermore, Nabhitabhata (1987) listed, without comments nor voucher specimens, Amphiesma modestum from Doi Suthep-Pui National Park, Chiang Mai Province, northern Thailand. This record may refer to Hebius khasiensis (see David et al. 2013), or, more likely, to Hebius deschauenseei (see below). Lastly, it should be noted that the treatise of “ Natrix modesta modesta ” in Bourret (1935b: 259 & 261 [Reprint p. 1 & 3]), Bourret (1936b: 73–74 [in part], 74: Fig. 30) and Bourret (1937: 27 & 29) refer to the new species, related to Hebius modestus , described below.

Mahendra (1984: 244) erected the genus Paranatrix (type species: Tropidonotus modestus G̹nther, 1875, now Hebius modestus , by original designation) for six species of the genus Hebius present in India. Furthermore, Mahendra (1984: 247) synonymized H. khasiensis with H. modestus . This synonymy is erroneous as these species are morphologically distinct from each other. These two species differ by (1) the shape of their internasals, abruptly truncated vs. distinctly narrowing in H. modestus , (2) the number of subcaudals, 87–111 vs. 104–122, (3) the pattern of supralabials, with distinct white, round, blotches vs. speckled with dark brown and scales edged with dark brown or blackish-brown, and (4) venter entirely pale vs. pale ochre-brown or pale brown on a wide central area, edged with dark brown.Additional characters can be found in David et al. (2013). However, the generic nomen Paranatrix is an available name if the genus Hebius has to be further split.

As conceived here, Hebius modestus is a well defined, purely Indo-Himalayan species that has a much more restricted range than that given by Smith (1943) or, for example by Nguyen et al. (2009) and Wallach et al. (2014) who considered H. modestus to be widespread from India to South Vietnam. This species is monotypic.

Diagnosis.—A moderately sized species of the genus Hebius characterized by the combination of (1) 19-19-17 dorsal scale rows, barely or weakly keeled at midbody and on the posterior part of the body, smooth on 1 st DSR; (2) dorsal scales around the base of the tail weakly keeled; (3) head moderately distinct from the neck; (4) eye large; (5) maxillary teeth 27–30, the last two moderately enlarged; (6) tail long, with a ratio TaL/TL at least equal to 0.28 in females, up to 0.32 in males; (7) VEN 143–163; (8) SC 104–122; (9) prefrontal scales 2; (10) 1 or rarely 2 anterior temporals, rectangular and elongate; (11) venter pale ochre-brown or pale brown on a wide central area, broadly edged with dark brown or blackish on the outer quarter of ventrals, rarely entirely dark except on its most anterior part; (12) dorsal colour dark greyish-brown, brown or dark brown; (13) dorsum usually scattered with blackish-brown or black spots or blotches; (14) on each side, a more or less conspicuous, ochre-yellow, ochre-red, orange-brown or reddish-brown stripe, often reduced to a succession of elongate blotches on the anterior part of the body, extending from the nape to the base of the tail on 4 th– 7 th or 5 th– 7 th DSR, often but not always irregularly edged below and above by a series of large blackish-brown blotches; (15) no postocular streak; and (16) a short but broad, horizontal, pale yellowish-brown streak on the sides of the neck before the dorsolateral stripe, plus a streak on the nape behind the parietals.

Comparison. Hebius modestus differs from the group of H. venningi , i.e., H. venningi , H. taronensis and H. nigriventer , with which it might be sympatric in northern India and Myanmar (Kachin State) by (1) the number of 19 DSR at midbody; (2) the general dorsal pattern, usually striped and with dark blotches above and below the dorsolateral stripe vs. not striped but chequered or, in H. nigriventer , with conspicuous, large dorsolateral blotches; (3) venter usually widely pale along its whole length, edged with blackish-brown, rarely entirely dark except on its most anterior part vs. (a) venter pale (coral red in life) mesially, on the anterior part of the body and dark, clouded posteriorly in H. venningi ; (b) venter both pale and dark, i.e. with a pale background on its anterior part with irregular dark crossbands and nearly uniform on its posterior part in H. taronensis and (c) venter nearly entirely very dark in H. nigriventer ; and (4) a conspicuous yellow streak on the sides of the neck.

Description (based on our specimens).—Body rather slender, elongate, cylindrical, barely stouter in large females; head elongate, subtriangular, moderately distinct from the thick neck, flattened anteriorly; snout elongate, obtuse or rectangular as seen from above, oblique seen in profile, flat, amounting for 25.2–28.6 % of HL, or 1.8–2.0 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 rather large, about 1.3–1.7 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 648 mm (SVL 440 mm; TaL 208 mm; specimen ZSI 15263) for a male. The longest known female is 618 mm long (SVL 433 mm, TaL 185 mm long; BMNH 76.2.16.1).

Ratio TaL/TL: 0.288 –0.326, with a weak sexual dimorphism (see below).

Dentition. 27–29 maxillary teeth gradually enlarging, the last 2 moderately enlarged, without diastema.

Body scalation. DSR: 19-19-17 rows in all examined specimens; scales rhomboedric, feebly or moderately keeled at midbody; scales of 1 st DSR smooth; scales around the base of the tail only weakly keeled.

VEN: 143–163 (plus 1 or 2 preventrals); SC: 104–122, all paired, with a strong sexual dimorphism (see below); cloacal plate divided.

Ratio VEN/SC 1.36–1.52, without sexual dimorphism (see below).

Position of the reduction to 6 scale rows around the tail: SC 21–29, 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: 1.7–2.5.

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, not elongate, about 1.6–1.7 times longer than high, vertically divided above and below the nostril, with the posterior part equal to anterior one; internasals rather small, short, subtriangular, in broad contact with each other, about 1.0– 1.1 times longer than wide, distinctly narrowing anteriorly with an anterior margin about 0.35–0.45 times the width of the posterior margin; 2 prefrontals rather small, short, wider than long, 0.9–1.2 times as long as internasals; frontal large and wide, shield-like, 1.4–1.6 longer than wide and 2.0–2.4 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, elongate and broad, 1.6–1.9 times longer than the frontal, or suture between parietals 1.1–1.2 times longer than frontal; 1/1 loreal, pentagonal, short and high, 1.2–1.3 times longer than high, in broad contact with the nasal; 1/1 (in 4/ 12 specimens) or 2/2 preoculars, upper one larger than lower one; 2/2 (in 2/ 12 specimens) or 3/3 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– 4 th SL or more rarely 2 nd– 3 rd SL (in 1/24 occurrences) or 3 rd– 4 th SL (2/24 occurrences) 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 2, posterior temporals, the most common formula being 1+1 temporals; 10/10 (9/ 9 in 1 specimen) infralabials, 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 overall dark, namely dark greyish-brown, chestnut-brown or dark brown, often distinctly darker on the back than on the lower sides; dorsum and lower sides ranging from nearly uniform, with only poorly defined very dark and paler areas, to distinctly scattered with very dark brown, blackish-brown or black spots; a broad dorsolateral stripe, ochre-yellow, yellowish-brown, ochre-red, orange-brown or reddish-brown extends on the 4 th– 7 th or 5 th– 7 th DSR from behind the neck to the base of the tail but is usually reduced to a succession of elongate blotches on the anterior part of the body, or is faint and entirely reduced to a succession of blotches along the whole length of the body, this dorsolateral stripe may be absent in nearly unpatterned specimens and is replaced by a series of ill-defined, paler reddish-brown areas; a series of darker brown or blackish-brown elongate blotches, on the top of the back on the 8 th DSR, next to the dorsolateral stripe or series of blotches, 1 scale long and high and longitudinally separated by 2 or 3 dorsal scales, sometimes absent; another series of irregular, elongate, darker brown or blackish-brown blotches below the dorsolateral stripe or series of blotches, on the 2 nd to 4 th DSR; these series of blotches are sometimes absent. The tail is brown as the upper surface of the body, with irregular darker blotches; if present on the body, the dorsolateral stripe or blotches are present on its dorsolateral part, or replaced by paler reddish-brown areas.

The head is dark greyish-brown or dark brown, irregularly mottled with diffuse darker brown areas; loreal and nasal sometimes with irregular pale brown areas; 1 st– 7 th or 1 st– 8 th supralabials usually creamish-yellow, yellowish-brown or pale brown, usually speckled with dark brown and all edged with dark brown or blackish-brown on their posterior edge, sometimes entirely dark with their central part barely paler; last supralabial either entirely dark or with its lower part pale; no postocular streak; a conspicuous horizontal, creamish-yellow, ochre-yellow or yellowish-brown streak often present on the side of the neck, extending from behind the corner of the mouth up to the beginning of the dorsolateral stripe or its first blotch around the 10 th ventral; this streak may be entirely absent in poorly patterned specimens without dorsolateral stripe; a short median streak behind parietals; no oblique streak behind the head forming a chevron on the nape; infralabials, chin and throat cream, pale yellow-ochre or pale brown, with scattered dark brown spots along the outer edges of chin shields and throat, sometimes heavily spotted with dark brown; infralabials strongly edged with dark brown on their both anterior and posterior edges, and often strongly speckled with dark brown, sometimes entirely brown.

The venter is always pale, i.e., beige, creamish-brown, pale yellow-ochre or pale brown on its whole length, nearly uniform or speckled with dark or blackish-brown dots along its middle, more heavily on its posterior part, progressively making the venter entirely dark on its last quarter in some specimens; outer part of each ventral with an irregular dark or blackish-brown blotch, progressively widening posteriorly, tips of ventrals usually pale as the inner part of the venter, producing an irregular, discontinuous ventrolateral stripe. Lower surface of tail either pale as the venter, heavily spotted with dark or blackish brown, or entirely dark brown or blackish-brown depending on the colour of the posterior part of the body; tip of tail very dark.

We have not seen any genuine specimen of Hebius modestus alive or depicted in life in the literature. As stated above, the specimen from Mizoram ( India) depicted by Ahmed et al. (2009: 154) as Amphiesma cf. modestum is indeed a specimen of Hebius venningi .

Hemipenes.—In situ, the hemipenis is short and thin, reaching the 8 th SC and forked near its tip, proximal part covered with short spines, 2 or 3 much larger; distal part covered with small, dense spines; sulcus spermaticus short and with small lips.

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

(1) Strongly by the difference in the ratio TaL/TL: males: 0.320 –0.326 (mean = 0.323, s = 0.003); females: 0.288 –0.307 (mean = 0.299, s = 0.007).

(2) Strongly by the difference in the number of subcaudals: males: 113–122 (mean = 117.0, s = 3.2); females: 104–109 (mean = 107.0, s = 2.2).

Distribution ( Fig. 12 ).— India. State of Meghalaya. Definitely known only from the Khasi Hills. State of Arunachal Pradesh. Tirip District; Lohit District ( Borang et al. 2005).— Myanmar. Kachin State. Bhamo District. Shan State. Tahò, 19°23’N, 96°54’E, Tauggyi District.— People’s Republic of China. Yunnan Province. Mangshi County and Yingjiang County (Dehong Dai and Jingpo Autonomous Prefecture), in the extreme western part of the province.

This species is probably also present in some other states of India, such as Nagaland, and in other districts of Kachin State in Myanmar, but it has yet to be found there.

As explained above, previous records of Hebius modestus from eastern Thailand, Cambodia, Laos, and Vietnam should be referred to other species, mostly Hebius boulengeri .

Biology.—This species inhabits evergreen or semi-evergreen submontane forest up to 1,600 m a.s.l. where it is seemingly associated with hill or montane forest streams. It inhabits the forest litter near these streams or in other riparian areas. Very little has been recorded about the biology of Hebius modestus . It probably feeds on tadpoles and frogs. Wall (1926) recorded a female, preserved between June and August, that contained three large eggs in its oviducts. This species is either secretive or rare.

Figures

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 12. Distribution map of species with 19 dorsal scale rows at midbody. Circles: Hebius modestus G̹nther. Squares: Hebius deschauenseei Taylor. Black triangle: Type locality of Hebius igneus spec. nov. White triangles: Hebius igneus spec. nov.

FIGURE 13. Hebius modestus (G̹nther), syntype (BMNH 1946.1.13.41)—A: dorsal view; B: ventral view; C: close-up dorsal view of the head; D: lateral view of the head, right side. Photographs: Gernot Vogel.