Isanophis boonsongi ( Taylor & Elbel, 1958 ) Taylor & Elbel, 1958

David, Patrick, Pauwels, Olivier S. G., Nguyen, Truong Quang & Vogel, Gernot, 2015, On the taxonomic status of the Thai endemic freshwater snake Parahelicops boonsongi, with the erection of a new genus (Squamata: Natricidae), Zootaxa 3948 (2), pp. 203-217 : 206-208

Isanophis boonsongi ( Taylor & Elbel, 1958) comb. nov.

( Fig. 1 A–D)

Parahelicops boonsongi Taylor & Elbel, 1958: 1156 , Fig. 31. Type locality. Mt. Phu Nam Lang, 1,780 m, Ban Khok, Na Phung, Dan Sai District, Loei Province, Thailand. Holotype. FMNH 135328 (originally EHT-HMS 31707), adult female; collected by Robert E. Elbel, 2 June 1955.

Material examined. Thailand. Loei Province. FMNH 135328 (holotype), see locality above.

Additional material. Specimens cited by Cox (1995) were deposited as TNRC 52-3884, and TNRC 52-3885, both adult, unsexed specimens from Nam San Noi Stream, Phu Ruea District, Loei Province, Thailand, 700 m a.s.l. In spite of extensive searches made by one of us ( O.S.G.P.) in August 2014, these specimens could not be traced. Nevertheless, M. J. Cox (pers. comm to PD, July 2012) kindly communicated some morphological characters of these two specimens which were used in the present paper.

Taxonomic comments. This species has been known from only the holotype until Cox (1995) recorded two additional specimens about 40 km east of the type locality. One of the specimens was depicted in Cox et al. (1998, 2012). This species is monotypic.

Diagnosis. See above the generic characters plus: (1) large size, up to at least 990 mm; (2) 19–19–17 DSR, all strongly keeled; (3) 29 maxillary teeth in the holotype, the last three distinctly enlarged; (4) a long tail, with a ratio TaL / TL reaching at least 0.24; (5) 136–140 VEN, 60 SC in the holotype; (6) 8–9 SL; (7) 2 anterior temporals; (8) body uniformly dark ochre-brown (dark chestnut brown in life), somewhat paler and more beige on the lower part of the sides (dark reddish-brown); and (9) venter uniformly pale ochre-brown (pale yellowish-brown in life).

Description. Body cylindrical, thick and stout; head elongate, well distinct from the neck, flattened; snout elongate, flat, broadly rounded, approximately 24 % of HL, or 1.1–1.4 times as long as the horizontal diameter of eye; nostrils placed dorsolaterally on the snout and directed obliquely upwards; eye diameter 1.5 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 total length known is 990 mm (SVL 750 mm; TaL 240 mm; specimen depicted in Cox et al. 1998, 2012).

Ratio TaL / TL: 0.242 in the only specimen with a complete tail (same specimen as above; sex unrecorded).

Dentition. 29–30 maxillary teeth, the last three distinctly enlarged, without diastema.

Body scalation. DSR: 19 – 19 – 17; scales notched posteriorly, strongly keeled throughout, with a thick keel; 1st DSR weakly keeled anteriorly, distinctly keeled posteriorly.

Scale row reductions (holotype): 19→17 DSR at VEN 78 (left) & 84 (right).

VEN: 136–140 (plus 1 preventral); SC: 60 in the only specimen with a complete tail, all paired; anal plate divided.

Ratio VEN / SC 2.33 (in the only specimen with complete tail). Position of the reduction to 6 scale rows around the tail: 11th SC.

Head scalation. Rostral wider than high, slightly visible from above; nasals subrectangular, elongate, vertically divided, with the posterior part shorter than anterior one; nostril small, oval, piercing in the middle of the nasal; internasals small, triangular, in broad contact, barely longer than the prefrontal, longer than wide, distinctly narrowed forward with an anterior margin about 0.4 times the width of the posterior margin, rounded posteriorly; prefrontal single, rather narrow, about twice as wide as long; frontal hexagonal, shield-like, rather small, 1.5 times longer than wide, about 2.2 times as long as the prefrontal; supraocular 1 / 1, large, subtriangular, longer than wide, nearly twice as wide as internasals; parietals large, much longer than the frontal; loreal scale 1 / 1, trapezoidal, as high as long, in broad contact with the nasal; SL 8 or 9, the first five higher than long; 1st, 2nd and 3rd SL small and short, in contact with the nasal, 3rd and 4th SL in contact with the loreal, SL 3–4, 4–5 or 4–6 entering orbit, 6th and 7th or 7th and 8th SL largest; 1 or 2 small suboculars usually present above SL 6; preoculars 1 / 1 (2 specimens) or 2 / 2 (1 specimen); postoculars 2–4, small; temporals 2+3, anterior ones larger; IL 10 / 10 in all known specimens, IL 1– 5 in contact with anterior chin shields, 6th IL largest; 1 pair of posterior chin shields much longer than anterior ones, narrowly divided anteriorly.

Coloration and pattern. The upper surface of the body is uniformly dark ochre-brown (dark chestnut brown in life), possibly with some very faint, irregular, darker areas, progressively paler and more reddish-beige on the lower part of the sides (dark reddish-brown in life), especially on the 1st and 2nd DSR. Tail as the body, paler on its lower sides.

Head dark ochre-brown (dark olive-brown in life), paler on the side of the snout and anterior SL (yellowishbrown); posterior supralabials pale greyish-yellow (yellow in life), contrasting abruptly with the upper head surface; IL, chin and throat uniformly pale ochre-brown (pale yellowish-brown), brighter yellow on IL and sides of the throat. Iris black.

Venter uniformly pale ochre-brown (pale yellowish-brown in life). Under surface of tail as the venter, irregularly mottled with dark greyish-brown.

Hemipenes. Unknown.

Sexual dimorphism. Unknown.

Distribution. Thailand. Isanophis boonsongi is known only from Dan Sai District and Phu Ruea [or Phu Rua] District, Loei Province. Based on the distributions of other species (e.g., Paratapinophis praemaxillaris Angel, 1929 ), we think it is likely to occur in north-western Laos.

Biology. This species has been recorded from 700 m up to 1,780 m a.s.l. Specimens mentioned by Cox (1995) were taken from a mountain stream.

Recognition of Isanophis requires a redefinition of Parahelicops , which is currently monotypic:

Figures

FIGURE 1. Isanophis boonsongi new comb., preserved holotype (FMNH 135328). From top to bottom: Dorsal view - Ventral view - Lateral view of the head and neck, left side. Photographs by Patrick David.