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Rhabdophis helleri (SCHMIDT, 1925)

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Higher TaxaColubridae (Natricinae), Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Subspecies 
Common NamesE: Heller’s Red-necked Keelback
G: Heller-Rothals-Wassernatter
Chinese: 红脖颈槽蛇 
SynonymNatrix helleri SCHMIDT 1925: 3
Natrix subminiata helleri — MELL 1931 [1929]
Rhabdophis subminiatus var. helleri — DEUVE 1961: 14
Rhabdophis subminiata helleri — TAYLOR 1965
Rhabdophis subminiatus helleri — ZHAO et al. 1986
Rhabdophis subminiatus helleri — NGUYEN et al. 2009
Rhabdophis helleri — LIU et al. 2021
Rhabdophis helleri — DAVID & VOGEL 2021 
DistributionChina (Yunnan, Guangxi, Guangdong, Fujian, Hong Kong, Sichuan, Guizhou), N Vietnam, Myanmar, India (Assam ?, Mizoram, Sikkim; Arunachal Pradesh [A. Captain, pers. comm.], Tripura), Bhutan, Bangladesh, Nepal

Type locality: Tengyueh, 5500 feet elevation, Province of
Yunnan, China, 25°01'N, 98°30'E.  
Reproductionoviparous 
TypesHolotype: AMNH 20149, paratype: FMNH 
DiagnosisDIAGNOSIS. Closely allied to Natrix subminiata of Java and southeastern Asia, from which it is distinguished by a higher number of ventral scales,163-172,compared with132-157 in subminiata as here restricted.
Dorsal scale rows 19, the outer smooth, the median rows sharply keeled; ventrals 163-172; anal divided; caudals 75-86; upper labials 7-9, three entering the eye; a single preocular; three postoculars; temporals 2-2; general color uniform olive, with reddish markings on the neck, chiefly confined to the skin between the scales (Schmidt 1925: 3).

Diagnosis. A large-sized species of the genus Rhabdophis characterized by the combination of (1) 19 (rarely 17, 18, 20 or 21) – 19 – 17(rarely 15) dorsal scale rows; (2) dorsal scales narrowly but strongly keeled, scales of 1st DSR smooth; (3) strong nuchal groove, well visible; (4) 2–8 distinctly enlarged, aligned nuchal scales; (5) VEN 157–178, SC 75–97, paired; (6) dorsum usually olive-green or dark greyish-green, or dark grey or brown, usually nearly uniform or chequered with black; (7) red hue on the neck present and usually conspicuous, although sometimes subdued; (8) dark subocular streak often totally absent or reduced to a few dots, or incomplete, or, more rarely, conspicuous; (9) when present, subocular streak shaped as a vertical bar or an incomplete triangle directed backwards, more or less faint and faded in its middle, rarely solid black and conspicuous, or as a broad comma; (10) venter cream or creamish-yellow anteriorly becoming on a short distance heavily dotted with dark grey backward.
Rhabdophis helleri can be easily distinguished from Rhabdophis subminiatus, as defined here, by the main following characters:
(1) the difference in total size, up to 130 cm in R. helleri vs. less than 80 cm in R. subminiatus;
(2) the number of ventrals: 157–178 (x = 165.3, sd = 3.6) vs. 132–145 (x = 136.8, sd = 2.6) in R. subminiatus;
(3) nuchal groove always present and strong vs. invisible;
(4) 3–8 (usually 5–7) enlarged, aligned paired nuchal scales vs. 0 aligned and enlarged scale (2 aligned pairs in only one specimen);
(5) no pale dorsolateral stripe or series of blotches vs. a pale dorsolateral stripe or a series of longitudinally aligned pale rectangular blotches usually present on 5th–6th dorsal scale rows in R. subminiatus;
(6) dark subocular streak often totally absent or usually reduced to a few dots, or incomplete, or, more rarely, conspicuous and directed downwards vs. most usually present and shaped as a narrow vertical bar or as narrow streak curved downwards or even forwards, rarely a broad vertical bar or as a thick streak in R. subminiatus.
(7) venter cream or pale creamish-yellow on a short distance anteriorly turning to heavily dotted or speckled with dark grey vs. venter always pale, i.e., cream or creamish-yellow, with usually a dark dot on the tips of each ventral in R. subminiatus (David & Vogel 2021).

Description of species. Body rather robust, distinctly stout in large females, cylindrical; nuchal groove strong, well visible; head elongate, thick but somewhat flattened, distinct from the neck; snout elongate, slightly depressed, obtuse as seen from above, oblique seen in profile, 1.7–2.2 times greater than the diameter of the eye; nostrils lateral and directed laterally, small, crescent-shaped, piercing in the middle of the nasal; eye rather large, its diameter about 1.4–1.8 times greater than the distance between its lower margin and the margin of the lip, with a round pupil; tail long, rather thick at its base, cylindrical and tapering.
The longest examined specimen is 1,107 mm long (SVL 865 mm; TaL 242 mm; specimen NHMUK 1926.3.17.1, female). The longest male in our sample is 999 mm long (SVL 723 mm, TaL 276 mm; NMW 22468:1). According to the literature, R. helleri may reach a total length of 130 centimetres. This species is much larger than R. siamensis. In our sample of 51 specimens, 17 are over 800 mm in TL and even six are over 900 mm in total length.
Ratio TaL/TL: 0.219–0.286, with a strong sexual dimorphism.
21–25 maxillary teeth on each jaw, gradually enlarging, the last two abruptly and very strongly enlarged, without diastema.
DSR: (17, 18)19(21) – 19 – (15)17 rows; scales strongly keeled with a narrow keel throughout the body; scales of 1st DSR smooth. In our sample of 51 specimens, 6 have 17 scale rows around the neck, one has 18 rows, one 20 rows whereas another one has 21 scale rows. Only one specimen has 15 DSR before vent.
Number of aligned, paired enlarged scales on the nape: 3–8 (usually 5–7), well visible and most often regularly aligned.
VEN: 157–178 (plus usually 2 preventrals, rarely 1 or 3); SC: 75–97, paired, with a clear sexual dimorphism; cloacal plate divided. Ratio VEN/SC 1.68–2.17 (x = 1.96, sd = 0.09).
Position of the dorsal scale rows reduction from19 to 17 DSR:VEN 82–93 (x=87.4,sd= 2.5).
Complement 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 pentagonal, elongate, much longer than high, vertically divided above and below the nostril, with the posterior part larger than the anterior scale; internasals subtriangular, in broad contact with each other, longer than wide, moderately narrowing anteriorly and abruptly truncated; 2 prefrontals, distinctly broader than long and 1.1–1.3 times longer than internasals; frontal large, shield-like, longer than wide and 2.2–2.4 times longer than prefrontal; 1 supraocular on each side, subtriangular, elongate, 2.0–2.4 times longer than wide, about as wide as internasals; parietals large and broad, 1.4–1.5 times longer than the frontal or suture between parietals 1.1–1.2 times longer than frontal; 1/1 loreal, pentagonal, not elongate, often higher than long or barely longer than high, in broad contact with the nasal; 1/1 preocular in all examined specimens; usually 3 small postoculars (very rarely 2, in four specimens, or 4 in six specimens); usually 8/8 SL (7/8 in 1/51 specimens only; 8/9 or 9/8 in 9/51; and 9/9 in 2/51), the first five as long as high or slightly higher than long, 1st and 2nd SL in contact with the nasal, 2nd or 2nd–3rd SL in contact with the loreal, usually 3rd–5th SL touching orbit, also 4th–6th in 14 specimens, rarely 4th–5th (in 6 specimens) or 3rd–4th in the sole specimen with 7 SL at left; 6th–7th SL distinctly the largest; 2 anterior temporals (3 in only 2/102 occurrences), much elongate, narrowing anteriorly, lower one largest, followed by 2 or 3 posterior temporals (4 in 2/102 occurrences), the most common total formula being 2+2 or 2+3 temporals; usually 10 infralabials, rarely 8 (in 1/102 occurrences) or 9 (in 6/102 occurrences), first pair in contact, most usually 1st–5th IL (rarely 1st–4th) in contact with anterior chin shields, 5th, 6th and 7th IL largest; posterior chin shields narrower and longer than anterior ones (David & Vogel 2021). 
CommentVenomous. Can inflict serious coagulopathic envenoming but, unlike its congener R. tigrinus, has not caused any human fatalities (Weinstein 2017).

Behavior: diurnal.

Distribution: For a map see David & Vogel 2021: 110 (Fig. 9). 
References
  • David, Patrick & Gernot Vogel 2021. TAXONOMIC COMPOSITION OF THE Rhabdophis subminiatus (SCHLEGEL, 1837) SPECIES COMPLEX (REPTILIA: NATRICIDAE) WITH THE DESCRIPTION OF A NEW SPECIES FROM CHINA. Taprobanica 10 (2): 89–120 - get paper here
  • Deuve, J. 1961. Liste annotee des Serpents du Laos. Bull. Soc. Sci. Nat. Laos 1:5-32.
  • Dutta, Sourav, Debajit Mahanta, Tilak Kumar Pradhan, Hirakjyoti Das & Monish Kumar Thapa. 2022. Caudal pseudoautotomy in Heller’s Red-necked Keelbacks, Rhabdophis helleri (Schmidt 1925). Reptiles & Amphibians 29(1): 212–213. - get paper here
  • Liu, Q., Xie, X., Wu, Y., Shu, G., Guo, K., Guo, P. and Cui, L. 2021. High genetic divergence but low morphological differences in a keelback snake Rhabdophis subminiatus (Reptilia, Colubridae). J Zool Syst Evol Res - get paper here
  • Mell,R. 1931. List of Chinese snakes. Lingnan Sci. Jour., Canton, 8 [1929]: 199-219.
  • Nguyen, S.V., Ho, C.T. and Nguyen, T.Q. 2009. Herpetofauna of Vietnam. Chimaira, Frankfurt, 768 pp.
  • Schmidt, KARL P. 1925. New reptiles and a new salamander from China. American Museum Novitates (157): 1-5. - get paper here
  • Taylor,E.H. 1965. The serpents of Thailand and adjacent waters. Univ. Kansas Sci. Bull. 45 (9): 609-1096 - get paper here
  • Wang K, Lyu ZT, Wang J, Qi S, Che J 2022. Updated Checklist and Zoogeographic Division of the Reptilian Fauna of Yunnan Province, China. Biodiversity Science 30 (4): 21326, 1–31 - get paper here
  • Zhao, E.; Liu, X.; Kang, S. 1986. Five snake species new to Sichuan [in Chinese]. Acta Herpetologica Sinica 5 (2): 157 - get paper here
 
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