Opisthotropis durandi, Teynié, Alexandre, Lottier, Anne, David, Patrick, Nguyen, Truong Quang & Vogel, Gernot, 2014

Teynié, Alexandre, Lottier, Anne, David, Patrick, Nguyen, Truong Quang & Vogel, Gernot, 2014, A new species of the genus Opisthotropis Günther, 1872 from northern Laos (Squamata: Natricidae), Zootaxa 3774 (2), pp. 165-182 : 167-175

Opisthotropis durandi spec. nov.

( Figs. 1–4 )

Holotype. — MNHN 2013.1001, an adult female, from the vicinity of Muang Ngoi (20°42'10"N, 102°41'21"E), Ngoi District, Louangphabang Province, Lao People’s Democratic Republic ( Laos), at an elevation of about 370 m a.s.l.; collected by Alexandre Teynié and Anne Lottier on 18 September 2012.

Paratype. — IEBR A.2013.26, an adult male, from Mork or Mok Waterfall (20°39'N, 102°42'E), at about 4 km east of Ban Sopkhong or Ban Sop Keng, a village on Nam Ou River located between Nuang Kiea and Muang Ngoi, Ngoi District, Louangphabang Province, Lao People’s Democratic Republic ( Laos), at an elevation of about 700 m a.s.l.; collected by Alexandre Teynié and Anne Lottier on 20 May 2013.

The locality of the paratype is at about 5.3 km south-southeast from the type locality.

Diagnosis. —A species of the genus Opisthotropis , characterized by a combination of the following characters: (1) 21–19 DSR at neck and 17 DSR at midbody, all smooth; (2) nostril narrow, long and strongly oblique, dividing the whole length of the nasal; (3) internasals triangular and strongly curved, in contact with the loreal; (4) 1 prefrontal; (5) frontal wider than long; (6) loreal large, longer than high; (7) 6/7 supralabials, 4th SL entering orbit on both sides; (8) 1 preocular; (9) 1 anterior and 2 posterior temporals; (10) at least 88 subcaudals; (11) about 22/23 subequal maxillary teeth; (12) upper dorsal surface above the 5th dorsal scale row uniformly dark greyish-brown with bronze tints, contrasting faintly with sides more bronze-brown, with scales broadly edged posteriorly with yellowish-ochre, this pigmentation extending downwards up to the 1st dorsal scale row; (13) venter pinkish-ochre brown; (14) head dark greyish-brown; and (15) chin, throat and 1st preventral largely blackish-brown with scales irregularly dotted or edged with ochre yellow.

A detailed comparison with the other known species of the genus Opisthotropis , especially the 10 species that have 17 dorsal scale rows at midbody, plus Parahelicops annamensis , is given below in “Comparison”. Nevertheless, the combination of a high number of dorsal scale rows at neck for a species with 17 DSR at midbody, internasal in contact with loreal, a high number of subcaudals, the uniform dorsal pattern, and the dark pigmentation of the throat abruptly contrasting with the pale colour of the venter, distinguish Opisthotropis durandi spec. nov. from all other species of the genus Opisthotropis .

Etymology.—This species is named in honour of Mr Frédéric Durand, president of the naturalist association “Société d’Histoire Naturelle Alcide d’Orbigny” (Clermont-Ferrand, France), who supported our field trips and researches of the two first authors in Laos, and thus contributed to the better understanding of the herpetology of Laos.

Suggested common names. Durand’s Mountain Stream Snake (English); Opisthotropis de Durand (French).

Description of holotype.—Body stout, cylindrical; head short (3.3 % of SVL), barely distinct from the thick neck, depressed, flat anterior to eyes, dorsally covered with large shields; snout long, 31.1% of HL or 3.2 times longer than diameter of eye, blunt, relatively subrectangular seen from above and in profile, depressed; nostrils in dorsal position and directed forwards, crescentic and very narrow, nearly reduced to the shape of a slit, strongly oblique, piercing the middle and nearly dividing the whole of nasal; eye small, its diameter about 0.7 times of the distance between eye and lip, with a vertically elliptic pupil; tail long and tapering progressively.

Measurements.—SVL: 408 mm; TaL: 130 mm; TL: 538 mm; ratio TaL/TL: 0.242; HL: 13.28 mm; SnL: 4.15 mm.

Dentition.—Maxillary teeth: right maxilla with 22 small but relatively thick, curved subequal teeth, without any diastema; left maxilla with 23 teeth.

Body scalation.—DSR: (21)19–17–17 scales, relatively large, imbricate scales, smooth throughout the body; DSR 1–2 slightly enlarged.

Dorsal scale row reductions:

6+7 → 6 (VEN 6) (left) 4+3 → 3 (VEN 15) (left)

21 ————————— 19 ————————— 17 6+7 → 6 (VEN 6) (right) 4+3 → 3 (VEN 21) (right)

177 VEN (+ 2 preventrals); 88 SC, all paired; cloacal plate divided.

Head scalation.—Rostral pentagonal, 1.5 times wider than high, visible from above; nasals large, distinctly directed forwards, subtriangular, much wider than high, obliquely divided by the long, narrow nostril and a short furrow below the nostril; internasals 2, narrow, triangular, strongly curved with its apex directed outwards and widely divergent each from the other, maximum width about 1.6 times greater than the suture between internasals or 1.2 times greater than maximum length; each internasal in contact with rostral, nasal, loreal and prefrontal; prefrontal single, broad but relatively narrow, subrectangular, much broader than long, in contact with the preocular and the loreal on each side; frontal hexagonal with its apex directed posteriorly, 1.5 times longer than prefrontal and 1.4 times wider than long; parietals long and wide, in contact for 1.1 times length of frontal; supraocular 1 / 1, small, about 0.25 times as wide as the frontal; loreal 1 / 1, subrectangular, large and entire, about 1.2 times longer than high, both broadly in contact with internasal on each side; preocular 1 / 1, large, about 0.8 times as high as eye diameter, not reaching frontal, in broad contact with prefrontal; postoculars 2 / 2, similar in size; at left, another scale, considered a “post postocular”, inserted between the lower postocular, anterior temporal, and 5th and 6th supralabials; subocular absent; supralabials 6 / 7, followed on each side, below the lower posterior temporal, by an enlarged, elongate scale that not border the lip; 1st–3rd SL distinctly higher than long (diagnostic characters of Opisthotropis ), 4th SL largest, 1.1 times higher than long, 5th–6th or 7th SL longer than high; 1st SL distinctly directed forwards; 1st and 2nd SL in contact with nasal, 2nd and 3rd SL in contact with loreal, 4th SL, large, entering orbit on both sides, 5th slightly shorter than 4th one but large, separated from orbit by the lower postocular, 6th SL at left, 6th and 7th SL at right distinctly shorter than 4th SL; temporals 1+2+3 / 1+2+3, anterior one largest and elongate, in broad contact with 5th and 6th SL and anterior part of parietal, middle temporals smaller, posterior temporals poorly differentiated from scales of the neck; infralabials 8 / 8, first pair in contact behind small mental, 1st–5th / 1st–4th IL in contact with anterior chin shields, 4th and 5th IL largest; posterior chin shields about 0.8 times as long as anterior ones, separated from each other by 3 scales.

Coloration.—In life, the upper dorsal surface above the 5th dorsal scale row dark greyish-brown with bronze tints; the whole of the neck and the sides of the body up to the vent rather pale bronze-brown or greenishyellowish-brown, paler than the dorsum, with scales broadly edged posteriorly with yellowish-ochre; the faint but sharp limit between the dark, upper and paler, lateral colourations, running on the centre of the 5th dorsal row; scales of the 1st dorsal scale row bronze-brown heavily mixed with the pale ochre-brown pigmentation of the venter. The dorsal surface of the tail is entirely dark greyish-brown as the dorsum, with some yellowish-ochre areas.

Head uniformly pale bronze-brown as the sides of the body, turning to dark greyish-brown on the snout and much of the frontal; parietals variegated with dark brown; four anterior supralabials dark greyish-brown, posteriors supralabials irregularly dotted or variegated with yellowish-ochre. Chin, throat and first preventral very dark greyish-brown, with some faint paler brown dots; this dark colour contrasts sharply with the pale ventral colour at the level of the 2nd preventral, nearly entirely pale; infralabials with traces of paler yellowish-ochre.

Venter pale pinkish brown or pinkish-ochre yellow, depending on lighting conditions, irregularly scattered with dark brown dots, especially present near their outer margins; cloacal scale with dark brown dots. Under surface of the tail strongly clouded with dark greyish-brown anteriorly, this pigmentation covering progressively the subcaudals; posterior part of the tail entirely dark greyish-brown, with some paler areas.

In preservative, the pattern and pigmentation are similar, although somewhat darker, but the limit between the dark dorsal and the paler lateral pigmentations is more or less visible and depends on the lighting condition.

Variation.—The paratype, an adult male ( Fig. 4 ), agrees in overall morphological characters, habitus, scalation, coloration and pattern with those given for the holotype. Differences are given below.

In taking into account the scalation data of the paratype, an adult male, main variation of Opisthotropis durandi spec. nov. are as follows:

Body. Ratio TaL/TL: 0.242 (female holotype); 0.255 (male paratype); (21)19–17–17 or 19–17–17 DSR; 177– 181 VEN (+ 2 preventrals); 88–90 SC, all paired.

Head scalation. Nasal large, obliquely divided by the long nostril in both specimens; 6 or 7 supralabials, 4th SL entering orbit on both sides in the holotype, 4th at right and 4th and tip of 5th at left in the paratype; 1 large preocular, 2 postoculars, equal in size; 1+2+3 / 1+2+3 temporals in both specimens; infralabials 8 / 8 in the holotype, 7 / 7 in the paratype; 1st–4th or 1st–5th IL in contact with anterior chin shields, 4th and 5th or 5th IL largest.

Comparison.—The comparison of Opisthotropis durandi spec. nov. with other species of the genera Opisthotropis and Paratapinophis and two species previously placed in the genus Opisthotropis , i.e. Parahelicops annamensis and “ Opisthotropis ” boonsongi , is based on examined specimens listed in Appendix and on the following references: Boulenger (1893), Pope (1935), Smith (1943), Brown and Leviton (1961), Taylor (1965), Toyama (1983), Ota and Mori (1985), Alcala (1986), Manthey and Grossmann (1997), Orlov et al. (1998), Zhao et al. (1998), Malkmus et al. (2002), Zhao (2004, 2006), Stuart and Chuaynkern (2007), Murphy et al. (2008), Ziegler et al. (2008), Iskandar and Kamsi (2009), David et al. (2011), and Yang et al. (2011, 2013).

Opisthotropis durandi spec. nov. differs by its number of dorsal scale rows at midbody (17) from following species with 19 rows: O. alcalai Brown & Leviton, 1961 , O. balteata ( Cope, 1895) , “ Opisthotropis boonsongi ” ( Taylor & Elbel, 1958), O. cucae David, Pham, Nguyen & Ziegler, 2011 , O. kuatunensis Pope, 1928 , O. typica ( Mocquard, 1890) , Paratapinophis praemaxillaris Angel, 1929 , and from O. laui with 23 rows.

Furthermore, Opisthotropis durandi spec. nov. differs from these species, at the exception of O. cucae , in having 21 dorsal scale rows on the neck vs. only 19 in the aforementioned species; O. cucae has 23 then 21 rows on the neck. Other noteworthy differences are as follows: Opisthotropis durandi spec. nov. differs from O. alcalai and O. typica in having a single prefrontal vs. 2 in these two species. Opisthotropis durandi spec. nov. differs from O. balteata , O. boonsongi , O. kuatunensis , and O. typica by its dorsal scales entirely smooth vs. keeled thoughout or at least posteriorly in these species. Opisthotropis durandi spec. nov. differs from O. balteata , “ O. boonsongi ”, O. kuatunensis , and P. praemaxillaris in having internasals in contact with loreal vs. separated in these species. With 177–180 ventrals, Opisthotropis durandi spec. nov. differs from O. boonsongi (136–140 VEN) and Paratapinophis praemaxillaris (145–155). Lastly, O. durandi spec. nov differs from O. balteata and P. praemaxillaris by its uniform pattern vs. crossbars in O. balteata and crossbands or large blotches in P. praemaxillaris . Other characters are given in Table 1.

With 17 dorsal scale rows at midbody, Opisthotropis durandi spec. nov. is readily distinguished from the group of five species with 15 scale rows which currently includes O. guangxiensis Zhao, Jiang & Huang, 1978 , O. jacobi Angel & Bourret, 1933 , O. kikuzatoi Okada & Takara, 1958 , O. maculosa Stuart & Chuaynkern, 2007 and Parahelicops annamensis Bourret, 1934 . However, P. annamensis may also rarely have 17 DSR at midbody.

Furthermore, Opisthotropis durandi spec. nov. differs from O. kikuzatoi and especially Parahelicops annamensis by its dorsal scales entirely smooth vs. moderately keeled posteriorly in O. kikuzatoi and strongly keeled throughout in P. annamensis . Opisthotropis durandi spec. nov. differs from O. guangxiensis , O. jacobi , O. kikuzatoi , and O. maculosa in having internasals in contact with loreal vs. separated in these four species. With 6 or 7 supralabials, Opisthotropis durandi spec. nov. differs from O. guangxiensis , O. maculosa and P. annamensis which have at least 8 SL. Lastly, by its uniform pattern O. durandi spec. nov differs from O. guangxiensis , O. kikuzatoi , and O. maculosa which have either crossbars or blotches. Other characters are given in Table 1.

Parahelicops annamensis may have 17 dorsal scale rows at midbody but it differs from Opisthotropis durandi spec. nov. by (1) a more slender body, (2) scales weakly keeled at midbody, strongly keeled posteriorly and around the base of the tail, (3) 28–34 maxillary teeth, the last two moderately enlarged, (4) at least 115 subcaudals, (5) ratio of TaL / TL at least 0.30, and (6) a dorsal pattern made of isolated orange or rusty blotches on a blackish-brown background.

Opisthotropis durandi spec. nov. shares the number of 17 dorsal scale rows at mid-body with 10 other species of the genus (excluding Parahelicops annamensise ), viz. O. andersonii ( Boulenger, 1888) , O. atra Günther, 1872 , O. cheni Zhao, 1999 , O. daovantieni Orlov, Darevsky & Murphy, 1998 , O. lateralis Boulenger, 1903 , O. latouchii ( Boulenger, 1899) , O. maxwelli Boulenger, 1914 , O. rugosa (Van Lidth de Jeude, 1890), O. spenceri Smith, 1918 , and O. tamdaoensis Ziegler, David & Vu, 2008 . Additional differences between these species are summarized in Table 1.

In details, Opisthotropis durandi spec. nov. differs from O. andersonii by its number of dorsal scales on the neck (21–19 vs. 17), its smooth dorsal scales throughout (vs. keeled throughout in O. andersonii ), a higher number of ventrals (177–180 vs. 149–169), internasal in contact with loreal (vs. separated), 6–7 SL (vs. 8–9), and its uniformly olive brown dorsal pattern (vs. uniformly dark with pale-edged scales).

Opisthotropis durandi spec. nov. differs from the holotype and sole known specimen of O. atra by its smooth dorsal scales throughout (vs. weakly keeled at midbody and strongly keeled posteriorly in O. atra ), a higher number of subcaudals (88–90 vs. 65 in the male holotype), 6–7 supralabials (vs. 8), 4th SL entering orbit (vs. 5th SL), 7th SL longer than high but not elongated (vs. much elongated), anterior chin shields distinctly longer than posterior ones (vs. subequal), and its uniformly olive brown dorsal pattern (vs. uniformly blackish-brown). Using the key provided by Yang et al. (2011) would lead to the identification of the type specimens of Opisthotropis durandi spec. nov. as O. atra . This flaw in the key points out the need to consider, in Natricidae , a combination of characters, even those often considered trivial, rather than a few “ major ” characters. O. durandi spec. nov. shares with O. atra the number of 19 dorsal scales on the neck, the long tail (ratio TaL/TL 0.220 in O. atra ) and other characters listed in Table 1.

Opisthotropis durandi spec. nov. differs from O. cheni by its number of dorsal scales on the neck (21–19 vs. 17), the loreal in contact with internasal (vs. not in contact), a higher number of ventrals (177–180 vs. 159–167), preocular present (vs. absent, loreal entering orbit), 6–7 SL (vs. 8–9), and its uniformly olive brown dorsal pattern (vs. dark with yellow crossbars).

Opisthotropis durandi spec. nov. can be separated from O. daovantieni in having 19 DSR on the neck (vs. 17), a much longer tail (ratio of Tal / TL 0.242–0.255 vs. 0.117–0.146), a lower number of ventrals (177–180 vs. 189– 194), a much higher number of subcaudals (88–90 vs. 39–47), 6–7 SL (vs. 8), and its uniformly olive brown dorsal pattern (vs. rather grey).

Opisthotropis durandi spec. nov. differs from O. lateralis in having 19 DSR on the neck (vs. 17), by its smooth dorsal scales throughout (vs. keeled throughout in O. lateralis ), the loreal in contact with internasal (vs. not in contact), 6–7 supralabials (vs. [rarely 9]10–11), 1 preocular (vs. 2), and the uniformly brown dorsal pattern (vs. dark with a conspicuous black lateral stripe that sharply contrasts with the pale coloration of the venter).

Opisthotropis durandi spec. nov. differs from O. latouchii by its number of dorsal scales on the neck (21–19 vs. 17), its smooth dorsal scales throughout (vs. keeled throughout in O. latouchii ), the loreal in contact with internasal (vs. not in contact), a higher number of ventrals (177–180 vs. 140–168), 6–7 supralabials (vs. 9), 1 preocular (absent in O. latouchii ), and the uniformly olive-brown dorsal pattern (vs. dark with broad yellow and narrow black lateral stripes).

Opisthotropis durandi spec. nov. can be separated from O. maxwelli in having 21–19 DSR on the neck (vs. 17), its smooth dorsal scales throughout (vs. keeled posteriorly in O. maxwelli ), the loreal in contact with internasal (vs. not in contact), a higher number of ventrals (177–180 vs. 147–158), and 1 preocular (vs. 2).

Opisthotropis durandi spec. nov. can be separated from O. rugosa by its smooth dorsal scales throughout (vs. strongly keeled throughout in O. rugosa ), 1 prefrontal (vs. 2 in three known specimens), and 6–7 supralabials (vs. 12–13).

Opisthotropis durandi spec. nov. can be separated from O. tamdaoensis by its smooth dorsal scales throughout (vs. keeled posteriorly), the loreal in contact with internasal (vs. not in contact), 6–7 supralabials (vs. 8–9), 1 anterior loreal (vs. 2), and the uniformly olive-brown dorsal pattern (vs. the presence of a black lateral stripe).

Lastly, Opisthotropis durandi spec. nov. is most similar to Opisthotropis spenceri , a species still endemic to Lampang Province, northern Thailand. Both species share most external characters, including the numbers of subcaudals (88–90 vs. 90–96 SC) and the numbers of supralabials, 6–7 in O. durandi spec. nov. vs. 7–8 (with 4th entering orbit in O. durandi vs. 4 or 4th–5th in O. spenceri ). Nevertheless, these species can be separated from each other by (1) the number of dorsal scales on the neck, 21–19 vs. 17 in O. spenceri ; (2) a different dorsal pattern, the dark dorsal reaching the 1st dorsal scale row along the limit of ventrals in O. durandi spec. nov., whereas the dark and pale ventral pigmentations mingle on 2nd or 3rd scale rows and cover entirely 3rd and 4th and upper dorsal scale rows; (3) chin, throat and 1st preventral dark brown, with a sharp transversal limit in O. durandi spec. nov., vs. chin, throat and 1st preventral pale greyish- or pinkish-brown with some dark brown dots in O. spenceri ; (4) under surface of tail largely dark brown in O. durandi spec. nov. vs. pale coloured as the venter, with dark brown dots, in O. spenceri , and (5) frontal 1.4 times wider than long in O. durandi spec. nov. vs. as long as wide in the three available specimens of O. spenceri .

Distribution ( Fig. 5 ). Laos. Louangphabang Province. Vicinity of Muang Ngoi in Muang Ngoi District, at an elevation of 370 and 700 m a.s.l. Opisthotropis durandi is known only from the type locality and its vicinity, a hilly region located in the north of Louangphabang Province.

Natural history. The general biotope of the holotype is a secondary evergreen forest growing over a steep slope at the foot of a karst formation ( Fig. 6 ). The snake was lying under a half-immersed rock at the bottom of a small waterfall in the course of a fast-running forest stream, with an average width of one meter. This stream runs across the forest just before it enters a cultivated valley. The snake was found at 11.00 h during a period of hot, sunny weather. A few water holes of various depths, some man-made, are present along the banks of the stream. These water holes are alternately or simultaneously inhabited by fish, tadpoles, and soft water shrimps and crabs, more rarely by larva of Odonata. The paratype was staying motionless, seemingly in ambush, at the beginning of the night, in the still, shallow (at most 40 cm deep) pool at the foot of Mok Waterfall (Fig. 7). The bottom of this piece of water is covered with sand and pebbles. Shrimps were observed in this pool. Another female specimen was seen 45 minutes later at about 400 m downstream of the pool. It was also staying motionless in a still part of the stream. Shrimps were also present.

The diet of O. durandi is unknown. The literature brings limited data on the diet of two species of the genus, O. andersonii and O. alcalai (Das 2010) . Possible preys present in the biotope of O. durandi include earthworms, tadpoles, small fish and especially fresh-water shrimps. It is interesting to note that the local vernacular name of this snake is Ngou Koung or Ngou Kung, meaning “Shrimp snake”.

Amphibian observed in or near the stream bed at the type locality include: Bufo (Duttaphrynus) melanostictus Schneider , Leptobrachium smithi Matsui, Nabhitabhata & Panha , Ophryophryne pachyproctus Kou , Xenophrys major (Boulenger) , Microhyla berdmorei (Blyth) , Microhyla fissipes (Boulenger) , Micryletta inornata (Boulenger) , Hoplobatrachus rugulosus (Wiegmann) , and Fejervarja limnocharis (Gravenhorst). Reptile species observed Calotes emma Gray , Eutropis multifaciatus (Kuhl) , Tropidophorus berdmorei (Blyth) , Enhydris plumbea (Boie in Boie), Lycodon subcinctus Boie , Pareas carinatus (Boie) , and Trimeresurus albolabris Gray. The broad range of species with different requirements result from the heterogeneous nature of the habitat that ranges from forest to rice fields.

Figures

FIGURE 1. Opisthotropis durandi spec. nov., preserved holotype (MNHN 2013.1001). A. Dorsal view. — B. Ventral view. — C. Lateral view of the head and neck, left side. — D. Ventral view of the tail. Photographs by Alexandre Teynié.

FIGURE 2. Opisthotropis durandi spec. nov., preserved holotype (MNHN 2013.1001), views of the head. A. Dorsal side. — B. Ventral side. — C. Right side. Photographs by Alexandre Teynié.

FIGURE 3. Opisthotropis durandi spec. nov., holotype (MNHN 2013.1001), alive in its natural biotope, vicinity of Muang Ngoi, Ngoi District, Louangphabang Province, Laos. A. General view. — B. Close-up view of head. Photographs by Alexandre Teynié.

FIGURE 4. Opisthotropis durandi spec. nov., paratype (IEBR A. 2013.26), alive in its natural biotope, Mok Waterfall, at about 4 km east of Ban Sopkhong, Ngoi District, Louangphabang Province, Laos. Photograph by Alexandre Teynié.

FIGURE 5. Map showing the type locality (black circle) of Opisthotropis durandi in Louangphabang Province, Laos.

FIGURE 6. Biotope of the holotype (A) and paratype (B) of Opisthotropis durandi. Photograph by Alexandre Teynié.