Oligodon saiyok Sumontha & Kunya & Dangsri & Pauwels 2017, sp. nov.
Creators: name: Sumontha, Montri
name: Kunya, Kirati
name: Dangsri, Siriwat
name: Pauwels, Olivier S. G.
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Squamata
Colubridae
Oligodon
Oligodon saiyok

description: Description of Oligodon saiyok sp. nov.
(Figs 1–7)
Holotype. QSMI 1506 (field number MS 469); adult male from Wat Tham Benjarat Nakhon (= Benjarat Nakhon Cave Temple), Sai Yok District, Kanchanaburi Province, western Thailand; collected by K. Kunya, M. Sumontha and S. Dangsri on 7 October 2009 at 18.00.
Paratype. QSMI 1 507 (field number MS 470), adult female, same locality and collector as holotype. It was found two hours later than the holotype.
Diagnosis. Oligodon saiyok sp. nov. can be distinguished from all other congeneric species by its maximal known SVL of 626.1 mm, 8 SL, 17-17-15 DSR, 181–187 VEN, single anal, 38–43 SC, 13 MT, a dorsal pattern with 21 or 22 large blotches or rings, and venter with a dense network of subrectangular dark blotches.
Description of holotype. Adult male. Body robust but elongate. Head short, neck moderately marked. Pupil round. SVL 626.1 mm. TaL 92.2 mm. Tail robust, tapering, accounting for 12.8 % of the TL (718.3 mm). HL 17.4 mm; HW 8.7 mm; HD 6.2 mm. SnL 4.7 mm. Snout short (27 % of HL, 1.9 times as long as ED). ED 2.5 mm.
Body scalation. DSR 17-17-15, all smooth. DSR reduction from 17 to 15 occurs above the 133rd VEN by fusion of rows 4 and 5 (left) and 3 and 4 (right). Two PV + 187 VEN, laterally angulated. Anal plate single. SC 43, all divided.
Head scalation. Rostral thick, curved onto upper snout surface, well visible from above, separating internasals by about one third of their length. Rostral width 2.6 mm, rostral height 2.1 mm. Nasals vertically divided. Nostril large, piercing top of middle of nasal. Internasals in broad contact, shorter than prefrontals. Prefrontals subrectangular, distinctly wider than long. Length of suture between internasals shorter than length of suture between prefrontals. Frontal pentagonal, 1.5 times as long as wide (frontal length 4.8 mm, frontal width 3.3 mm); 1/1 supraoculars, distinctly longer than wide; SL 8/8, 2nd and 3rd in contact with LOR, 4th and 5th in contact with orbit. LOR 1/1, distinctly longer (1.8 mm) than high (0.7 mm). PreOc 1/1, tall and narrow; no PreSubOc. PosOc 2/ 2, the upper one larger. Tem 1+2 on each side. Mental width 1.9 mm, mental length 1.2 mm. IL 8/8, 1st pair in contact behind mental, IL 1 to 4 in contact with anterior chin shields. First pair of chin shields distinctly longer than 2nd pair.
Dentition. Thirteen MT, curved backwards, sharp, the two posterior ones enlarged, kukri-like. Hemipenes. The hemipenes in situ reach the 18th SC.
Coloration in life. Dorsal surface of head grayish brown as the dorsum, but paler on the sides of the snout and rostral. Four chevron marks pointing frontwards on the head and neck. Chevrons blackish brown, somewhat paler grayish brown in their center, edged by darker pigmentation. Anteriormost chevron with its apex at the level of the posterior edge of the rostral, covering part of the internasals, prefrontals and frontal, and descending through the eye to cover part of the 5th and 6th SL. Second chevron with its tip in the middle of the frontal, covering part of the frontal, parietals, temporals and descending behind the mouth angle to the ventrals. Third chevron with its anterior tip on the parietals, covering part of the parietals and the nape. Fourth chevron smallest, located midway between the third chevron and the first dorsal blotch. Dorsum surface grayish brown, with all dorsal scales finely but densely dotted with blackish brown. A series of 21 blackish brown blotches on dorsum, somewhat paler grayish brown in their center, edged by darker pigmentation, 2 or 3 DSR long and 5 or 6 DSR broad, i.e. covering the vertebral scale row and 2 or 3 adjacent rows. First blotch located at 14 scales behind parietals. An irregular blackish transversal zig-zag separates chevrons. Some irregular blackish marks on lower flanks under each chevron. Five similarly colored blotches above tail. No dorsal stripes. Ventral surface of head uniform cream. Belly cream with numerous subrectangular dark grayish brown blotches increasing in density posteriorly. Underside of tail cream with some subrectangular dark grayish brown blotches anteriorly. Iris light golden brown, speckled with black.
Variation. Table 1 presents the main meristic and morphometric characters for the holotype and the paratype. The largest known specimen is the holotype. The relative tail length (TaL/TL) for the female paratype is 11.6 %, i.e., slightly shorter than in the male. The paratype’s frontal is 1.4 times as long as wide (frontal length 4.2 mm, frontal width 2.9 mm). In the paratype, the DSR reduction from 17 to 15 occurs above the 131st VEN by fusion of rows 4 and 5 on the left side and fusion of rows 3 and 4 on the right side. The most noticeable difference between the holotype and the paratype is the dorsum color pattern (see Figs. 5 and 7). Contrary to the male holotype, the female paratype does not show dorsal dark blotches but well-defined white rings bordered by a black line, in a number that is comparable to the number of blotches in the male holotype. Excluding the similarly colored chevron on the nape, the dorsum displays 22 such rings and the tail 4. These rings do not fully encircle the body as they do not reach the ventrals. The posterior rings are less contrasted than the anterior ones. The color of the iris in life is the same as in the holotype.
Distribution and natural history. Oligodon saiyok sp. nov. is currently known only from its type locality in Sai Yok District (Figs. 8 and 9). Both individuals were found active at night (18.00 and 20.00 respectively) in a Buddhist temple at the entrance of a cave on a limestone hill. They were rather aggressive when caught.
Other reptiles we found in syntopy at the type locality include Cyrtodactylus cf. peguensis (Boulenger) and C. tigroides Bauer, Sumontha & Pauwels, 2003, Dixonius hangseesom Bauer, Sumontha, Grossmann, Pauwels & Vogel, 2004, Gekko gecko (Linnaeus) and G. nutaphandi Bauer, Sumontha & Pauwels, 2008 (Gekkonidae), and Trimeresurus kanburiensis Smith (Viperidae). Syntopic amphibians we observed included Duttaphrynus melanostictus (Schneider) (Bufonidae), Kaloula pulchra Gray, Micryletta inornata lineata (Taylor) (Microhylidae) and Polypedates megacephalus Hallowell (Rhacophoridae). A color pattern dimorphism similar to the one observed in Oligodon saiyok sp. nov. has been documented for O. purpurascens by van Rooijen et al. (2011). The blotched pattern provides a cryptic coloration in the leaf litter, while the conspicuous ringed pattern suggests a mimicry of an aposematic signal, as noted by van Rooijen et al. (2011); these latter authors did not mention any link between the pattern observed and the sex of the individuals.
Etymology. The specific epithet is an invariable noun in honor of the administrative district where the typelocality lies. We suggest the following common names: Ngu Ngod Sai Yok (Thai), Sai Yok Kukri Snake (English), Oligodon de SaÏ Yok (French), and Sai Yok Kukrinatter (German).
description: Published as part of Sumontha, Montri, Kunya, Kirati, Dangsri, Siriwat & Pauwels, Olivier S. G., 2017, Oligodon saiyok, a new limestone-dwelling kukri snake (Serpentes: Colubridae) from Kanchanaburi Province, western Thailand, pp. 316-328 in Zootaxa 4294 (3) on pages 317-319, DOI: 10.11646/zootaxa.4294.3.2, http://zenodo.org/record/844788