Oligodon phangan, Pauwels & Thongyai & Chantong & Sumontha, 2021

Pauwels, Olivier S. G., Thongyai, Kanokorn, Chantong, Pajapon & Sumontha, Montri, 2021, Two new Kukri Snake species (Colubridae: Oligodon) from the Nakhon Si Thammarat Mountain Range, and addition of O. ocellatus to the fauna of Thailand, Zootaxa 4908 (4), pp. 537-557 : 539-544

Description of Oligodon phangan sp. nov.

( Figs 1–5 )

Holotype. PSUZC-R 732 (field number MS 631); adult female found in Wat Phu Khao Noi (9°44’02.8”N, 99°59’25.1”E), Ko Pha-Ngan Sub-district, Ko Pha-Ngan District , Pha-Ngan Island (= Ko Pha-Ngan or Koh Phangan), Surat Thani Province, peninsular Thailand; collected by P. Chantong on 20 December 2018.

Paratype. PSUZC-R 733 (field number MS 632); adult male; same locality and collector as holotype, collected on 15 December 2018 .

Diagnosis. Oligodon phangan sp. nov. can be distinguished from all other congeneric species by a combination of its maximal known SVL of 369.1 mm; 12 maxillary teeth, the posterior three enlarged; two internasals; two prefrontals; eight supralabials; loreal present; two postoculars; 17-17-15 dorsal scale rows; 163–166 ventrals and 33–42 divided subcaudals; a single anal; dorsal color brown with a pair of discreet paravertebral and lateral stripes; no dorsal or supracaudal bands, blotches or crossbars; background color of belly pinkish-orange; underside of tail immaculate.

Description of holotype. Adult female. Body robust but elongate. SVL 358.3 mm; TaL 53.2 mm. Tail robust, tapering, accounting for 12.9 % of the TL (411.5 mm). Pupil round. Head short (HL 13.2 mm, i.e. 3.7 % of SVL; HW 7.3 mm; HD 5.3 mm), barely distinct from the poorly marked neck. SnL 4.5 mm. Snout long (34 % of HL, 2.1 times as long as ED). ED 2.1 mm; ELip 1.8 mm; distance eye-nostril 2.3 mm. Straight distance between nostrils 3.4 mm. Distance between eyes 5.6 mm.

Body scalation. DSR 17-17-15, all smooth. DSR reduction from 17 to 15 occurs above the 93 rd VEN (left) and 95 th VEN (right) by fusion of DSR 3 and 4. 1 PV + 163 VEN, laterally angulated. Anal plate single. SC 33, all divided.

Head scalation. Rostral thick, curved onto upper snout surface, well visible from above, separating internasals by about one half of their length. RosW 2.6 mm, RosH 2.3 mm. Nasals vertically divided, with the posterior part smaller. Nostril large, piercing top of middle of nasal ( Fig. 4A ). Two internasals, in broad contact, shorter than prefrontals. Two prefrontals, subrectangular, distinctly wider than long. Length of suture between internasals (0.9 mm) shorter than the length of suture between prefrontals (1.3 mm). Frontal pentagonal, frontal length 4.2 mm, 1.3 times as long as wide; 1/1 supraoculars, distinctly longer (3.3/ 3.1 mm) than wide (2.2/2.0 mm); on the left side 7 SL, only the 4 th in contact with orbit (the long 4 th SL seems to result from a fusion of two SL, because a segment of a suture is still visible at the level where the 3 rd and 4 th SL are separated on the right side of the head); on the right side 8 SL, 4 th and 5 th in contact with orbit; on both sides 2 nd and 3 rd SL in contact with LOR; posterior three SL distinctly enlarged. LOR 1/1, distinctly longer than high ( Fig. 4A ). PreOc 1/1; no PreSubOc; no SubOc. PosOc 2/2, the upper one larger on each side. Tem 1+2 on each side. Parietals length 3.7/4.0 mm; parietals larger than the frontal, in contact on 3/4 of their length behind the frontal. Parietals bordered posteriorly by four undifferentiated dorsal scales. Mental width 1.8 mm, mental length 1.1 mm. IL 8/8, 1 st pair in contact behind mental, IL 1 to 4 in contact with anterior chin shields. First pair of chin shields much longer (3.5/ 3.4 mm) than 2 nd pair (1.9/ 1.7 mm). Second pair of chin shields in contact on each side with the 4 th and 5 th IL.

Maxilla dentition. Twelve MT, the three posterior ones enlarged, kukri-shaped; no diastema.

Coloration in life. Dorsal surface of the head light brown, with poorly contrasted, difficult-to-see darker marks: an interorbital transversal bar and a suborbital bar. The lateral sides of the head are light brown, lighter on the supralabials. The dorsum is light brown. Two paravertebral stripes, poorly contrasted as they are slightly darker than the background color, each less than two dorsals wide, begin on the neck and run along the dorsum. Two parallel lateral stripes, similarly poorly contrasted, less than one dorsal wide. The ventral color of the head is pinkish white. The belly is pinkish-orange, with light speckling posteriorly. No dark blotches on belly. The underside of tail is pinkishorange, without any speckling or dark marks. In preservative, the general color darkens, and the dorsal vertebral stripes nearly disappear; the belly and underside of tail become whitish.

Variation. Main morphological characters of the paratype are provided in Table 1; they agree in most respects with the holotype. Tail of the male paratype accounting for 16.6 % of its TL, suggesting that males probably have proportionally longer tails than females. Hemipenes of the male paratype are not everted, and the hemipenis structure of this species is still unknown. The possession on each head side of the paratype of eight supralabials of which the 4 th and 5 th contact the eye indicates that this is the normal configuration in the species, and that the near-complete fusion of two supralabials on one side of the head of the holotype is an abnormality. Live coloration of the paratype is similar to the holotype.

Distribution and natural history. Oligodon phangan sp. nov. is currently known only from its type-locality on Pha-Ngan Island in Surat Thani Province ( Fig. 9 ). The island belongs to the northern part of the Nakhon Si Thammarat Mountain Range, a mountain chain located about 60 km east of the Phuket Mountain Range and running parallel to it. Pha-Ngan Island lies at about 50 km from the mainland of Surat Thani Province; in between one finds Samui Island (Ko Samui) and small islets. A Naja aff. kaouthia Lesson individual was observed in direct proximity to the types of Oligodon phangan sp. nov. at the type-locality.

The types of Oligodon phangan sp. nov. were collected at night, along a wall of the temple. They were kept in captivity and refused any food, but were observed mating on 21 December 2018, thus shortly after having been collected. We have never encountered Oligodon phangan sp. nov. in the pet trade. The presence of Oligodon phangan sp. nov. in the nearby Than Sadet Waterfall National Park should be checked to ensure that the species is represented in a protected area.

Etymology. The specific epithet is a noun in apposition, invariable, referring to Pha-Ngan Island where the type-locality lies. We suggest the following common names: Ngu Pee Kaew Ko Pha-Ngan (Thai), Pha-Ngan Kukri Snake (English), Oligodon de Pha-Ngan (French) , and Pha-Ngan Kukrinatter (German).

Comparisons of Oligodon phangan sp. nov. with other species. Its single anal plate separates Oligodon phangan sp. nov. from the following species which show a divided anal plate: O. catenatus , O. cruentatus , O. dorsalis , O. eberhardti , O. jintakunei , O. mcdougalli , O. planiceps and O. theobaldi . With its 17 MSR, Oligodon phangan sp. nov. is easily distinguished from Oligodon annamensis (13), O. catenatus (13), O. cyclurus (19), O. dorsalis (15), O. eberhardti (13), O. fasciolatus (21), O. inornatus (15), O. jintakunei (15), O. kampucheaensis (15), O. mcdougalli (13), O. ocellatus (19), O. planiceps (13), O. purpurascens (19 or 21), O. rostralis (15), O. taeniatus (19) and O. vertebralis (15). Its striped, non-reticulated, non-blotched, dorsal pattern allows distinguishing it from Oligodon annamensis (banded), O. arenarius (indistinct pattern), O. barroni (blotched), O. booliati (banded), O. cattienensis (blotched), O. cinereus (indistinct/banded pattern), O. cruentatus (reticulated), O. cyclurus (reticulated/blotched), O. fasciolatus (reticulated/blotched), O. inornatus (patternless), O. jintakunei (banded), O. joynsoni (reticulated/ banded), O. kampucheaensis (banded), O. moricei (striped and reticulated), O. mouhoti (two blotches above tail), O. ocellatus (reticulated/blotched), O. planiceps (reticulated), O. purpurascens (blotched/reticulated), O. rostralis (blotched/reticulated), O. saintgironsi (blotched/reticulated), O. saiyok (banded/blotched), O. signatus (blotched /banded) and O. vertebralis (blotched). The VEN number of Oligodon phangan sp. nov. (163 – 166) is distinctly higher than in O. arenarius (131 – 144), O. booliati (143 – 153), O. deuvei (140 – 155), O. planiceps (132 – 145), O. pseudotaeniatus (137 – 156), O. signatus (141 – 157), and O. vertebralis (136 – 154), and distinctly lower than in O. jintakunei (189), O. joynsoni (186 – 198), O. mcdougalli (199) and O. saiyok (181 – 187). Its possession of 12 MT distinguishes Oligodon phangan sp. nov. from O. annamensis (8), O. arenarius (6 – 8), O. catenatus (7), O. cattienensis (8 – 10), O. cruentatus (14 – 16), O. cyclurus (9 – 10), O. dorsalis (6 – 7), O. eberhardti (7), O. fasciolatus (9 – 10), O. huahin (6), O. jintakunei (6), O. kampucheaensis (11), O. macrurus (13), O. mcdougalli (6), O. mouhoti (14 – 16), O. ocellatus (9 – 11), O. octolineatus (9 – 10), O. planiceps (10), O. pseudotaeniatus (15), O. purpurascens (9 – 10), O. rostralis (6), O. saiyok (13), O. signatus (7 – 8), O. taeniatus (14 – 17), O. theobaldi (15 – 16) and O. vertebralis (8 – 9) (number of MT unknown in O. booliati ). Oligodon phangan sp. nov. shows morphological similarities with the Vietnamese O. condaoensis , endemic to Hon Ba Island, from which it can be separated by its lower VEN number (163 – 166 vs. 168 – 176), higher SC number in males (42 vs. 37), its pinkish-orange (vs. cream to grayish) belly, and the absence (vs. presence) of dark dots under the tail.

Figures

FIGURE 1. Forebody of the holotype of Oligodon phangan sp. nov. (PSUZC-R 732) in life. Photograph by M. Sumontha.

FIGURE 2. Live holotype of Oligodon phangan sp. nov. (PSUZC-R 732) in ventral view. A red line marks every 10 ventrals and every 10 subcaudals. Photograph by M. Sumontha.

FIGURE 3A–B. Preserved holotype of Oligodon phangan sp. nov. (PSUZC-R 732) in dorsal (A) and ventral (B) views. Photographs by M. Sumontha.

FIGURE 4A–B. Head of the preserved holotype of Oligodon phangan sp. nov. (PSUZC-R 732). Left profile (A); ventral surface (B). Photographs by M. Sumontha.

FIGURE 5. Live paratype of Oligodon phangan sp. nov. (PSUZC-R 733) in pre-shedding phase. Photograph by M. Sumontha.

FIGURE 9. Map of Thailand showing the geographical locations for Oligodon phangan (yellow) and O. promsombuti (red) spp. nov. and the first known Thai locality for O. ocellatus (blue). Type-localities are indicated by a star. Map by W. Sodoab.