Oligodon bivirgatus, Qian & Qi & Shi & Lu & Jenkins & Mo & Li, 2021

Qian, Tianyu, Qi, Shuo, Shi, Jingsong, Lu, Yuyan, Jenkins, Robert W. G., Mo, Yanni & Li, Pipeng, 2021, A new species of Oligodon H. Boie in Fitzinger, 1826 (Squamata: Colubridae) from Hainan Island, China, Zootaxa 4933 (3), pp. 403-421 : 408-417

Oligodon bivirgatus sp. nov.

Figures 2–5

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Holotype: SYNU 1907027 , adult female, collected on 13 July 2019 by Tianyu Qian and Minghong Huang from Shangxi Nature Reserve (18.834167° N, 110.130833° E; 319 m a.s.l.), Hainan Province, China.

Paratype: SYNU 1808001 , adult female, collected on 17 August 2018 by Pipeng Li, Tianyu Qian and Minghong Huang from the same valley as the holotype (18.833611° N, 110.130556° E; 317 m a.s.l.) .

Etymology. The specific name comes from Latin words “ bi -” (double) and “ virgatus ” (striped), refers to this species has a dorsal color pattern made of two distinct dorsal stripes. The common name is recommended to read “Double Striped Kukri Snake” in English while it is “ Aäṁn'ḃ (Shuāng Xiàn Xiǎo Tóu Shé)” in Chinese.

Diagnosis. Oligodon bivirgatus sp. nov. can be distinguished from its congeners known to occur in Southern China and mainland Southeast Asia by having the following combination of characters: (1) eight maxillary teeth; (2) nasal divided; (3) absence of a loreal; (4) single preocular and two postoculars; (5) seven supralabials, third and fourth touching the orbit, sixth excluded from the lip; (6) seven infralabials, anterior four contacting chin shields; (7) internasals separate from prefrontals; (8) single anterior and two posterior temporals; (9) anal plate divided; (10) 15/15/15 dorsal scale rows; (11) dorsum reddish-brown in life, with two distinct narrow dark stripes, two dorsolateral lines are faintly visible; and (12) ventral surface reddish in life, edge cream with irregular dark blotches.

Description of holotype. Body slender, TL 465 mm, TaL 61 mm, SVL 404 mm; tail robust, tapering and quite short, Tal/TL ratio 13.1%; head short, HL 16.8 mm, HW 9 mm, slightly flattened, HH 6.3 mm, neck moderately marked; snout elongate, SnL 5.1 mm, SnL/HL ratio 30%.

Head scalation. Details of head scalation are shown in Figure 3 . Head scalation includes single rostral, two internasals, two prefrontals, two supraoculars, single frontal, and two parietals from dorsal view. Rostral shield large, thick, in contact with first supralabial, nasal and internasals posteriorly, curved onto upper snout surface, well visible from above; internasals in narrow contact, separated by a median suture; prefrontals sub-rectangular, width greater than length, separated by a suture; suture between internasals about equal to that between prefrontals; frontal large, pentagonal, posterior portion pointed, contacting parietal; supraoculars sub-rectangular, length greater than width distinctly, anterior narrower; parietals large, suture between parietals slightly shorter than length of frontal; nasal vertically divided, posterior part distinctly smaller, nostrils open in anterior part of nasal; loreal absent; pupil round, ED 2.2 mm, IO 5.4 mm; 1/1 vertically elongate, rectangular preocular; 2/2 rectangular postoculars; 1/1 anterior temporals, sub-rectangular, twice longer than wide, 2/2 posterior temporals, upper one smaller; 2 pair of chin shields, anterior pair elongate, the length is one third of the width, posterior pair sub-rectangular; SL 7/7, 1 st and 2 nd contacting nasal, 2 nd contacting internasal, 2 nd and 3 rd contacting preocular, 3 rd and 4 th contacting orbit, 4 th and 5 th contacting lower postocular, 6 th excluded from the lip, 5 th and 7 th barely distinguishable in size; IL 7/7, 1 st pair in contact with each other, 1 st– 4 th contact with anterior chin shields, 4 th largest, touching posterior chin shields.

Body scalation. Dorsal scale rows 15/15/15, all smooth; vertebral scales similar to other dorsal scales in shape and size; ventral scales 173, angulate laterally; anal plate divided; subcaudals 37, all paired, terminal caudal scale forming a tip.

Coloration of holotype. In life: Dorsal surface of head reddish-brown as dorsum, but paler on snout and rostral. Three pointing forward chevrons on head and neck. Chevrons maroon, somewhat paler maroon in the mesial, edged by darker pigmentation. The first chevron with its apex at the level of the posterior edge of the rostral, covering part of internasals, prefrontals, supraoculars and frontal, and descending through the eye to cover 3 rd– 5 th SL. The apex of the second chevron starts at the middle of head and covers the posterior part of frontal, extending to neck on both sides of the head, through parietals, upper anterior temporals, two posterior temporals, and descending behind the head, covering part of 7 th SL and 7 th IL. The third chevron, with its anterior tip on the suture of parietals is connected to the second chevron in the middle, forming an arrow, this arrow gradually widens and extends from parietals to the nape. The two edges of this arrow extend to dorsal as two narrow dark stripes, ending at the tip of tail. At the beginning of dorsal stripes, there are small blotches at the lateral of neck, about 3 rows scale rows behind head. The dorsal stripes are about 1/3 scale wide, covering 6 th and 10 th scale rows; another two dashed lines are faintly visible on the flanks. Ventral surface of head cream with black spots on the anterior portion of 1 st, 3 rd– 6 th SL, anterior chin-shields, other small spots at the midline of the gular scales. Belly is coral-red with its edge cream and black blotches irregularly distributed on each side. The blotches are small on the body, at intervals of one or two ventral scales, sometimes continuous, 95 on left and 100 on right. Ventral surface of the tail shows the same pattern as the belly. On the tail, the blotches become denser and no more intervals at the end 10 pairs of subcaudals, 27 on left and 25 on right. Iris bicolored, upper part light yellow, lower part brown, matching the dorsal pattern; pupil round, black with golden edge.

In preservative: The dorsal color became paler and, eventually, totally grey. The head mark and the dorsum stripe remained maroon. The coral belly faded to white, black blotches on belly lightened and, as a consequence, reduced in size.

Skull. The description of the skull of Oligodon bivirgatus sp. nov. is based on the three dimensional (3D) reconstructed model of the holotype (SYNU 1907027, Figure 5 ) and paratype (SYNU 1808001). Dorsally, the skull of Oligodon bivirgatus sp. nov. is roughly oval in shape. Nasal bones are slender and triangularly shaped, bilateral nasal bones fused at the posterior 2/3 part. The anterior part of the maxilla (in front of the ectopterygoid process) presents as lamella shaped. Dorsal-lateral ridge conspicuously ranges throughout the maxilla. Maxilla bears eight maxillary teeth on each side: two small normal teeth and six blade-like teeth, increasing in size posteriorly (the rearmost one largest), not separated by any diastema. The cutting edge of the blade-like teeth bulges posteriorly. Thus, the blade teeth look quite similar to the kukri knives. In contrast to most colubrid snakes, a small empty tooth position (one diastema in size) presents on the rostral tip of the ventral edge of the maxilla, which forms a small round-cornered process with the anterior part of the maxilla.

Septomaxilla quite wide and flat. The conchal process of septomaxilla slightly curved posteriorly. Vomer quite robust and short. The anterior tip of vomer is rounded and bunt. The ascending process of premaxilla is quite short and considerably slanted anteriorly, barely contacting the nasals near the rostral bottom tip of the vertical laminae. The palatine is lamellar, the choanal process of palatine is quite slender, round cornered and ventrally curled. The maxilla process of palatine is round and bunt, slightly ventrally curved. One section of small vacuity (approximately two palatine teeth in distance) presents at the tip of the ventral edge of the rostral, which form a small round-corner process in the anterior part of palatine. Ectopterygoid quite short, thick and robust, the angular surface to the maxilla is spanner-shaped. Postorbital slender, rostrally curved and elongated, not contacting the frontal.

Supratemporal bone is slender and triangular; the quadrate-connecting surface takes up about 3/4 the length of the total supratemporal. The anterior and posterior tip are slightly sharp in shape.

Quadrate bone triangular, roughly perpendicular to the mandible, the angular surface to the supratemporal is quite wide and the one to mandible is thick and robust.

Mandible: Compound bone quite slender and prominently curved ventrally. A prearticular crest is prominent and rounded. Two large oval foramina nutricia on the labial side of the dental bone.

Dentition. Maxillary teeth 8/8 (2+6); palatine teeth 4/4 (3/4); dentary teeth 13/11 (11/10); pterygoid teeth: asymmetry in number, 9/4 (8/4), degenerated in size, significantly smaller than the ones on the palatomaxillary arch and dental bones.

Variation. Morphological traits and pholidosis of two type specimens are listed in Table 4. The paratype matches most characters of the holotype, but there are little differences between them.

Scalation. The internasals are not in contact with the posterior part of nasal in holotype ( SYNU 1907027 ), but contacting in the paratype ( SYNU 1808001 ) .

Coloration. There are two differences in dorsal coloration on head between the paratype (SYNU 1808001) and the holotype (SYNU 1907027): 1. (Paratype) The tip of the second chevron on head is in the middle of frontal and in contact with first chevron, a gap is formed in back of the middle, but no contact and divided posterior portion in holotype; 2. (Paratype) The third chevron commences at the posterior end of parietals with a blunt tip. The condition of the third chevron in the holotype differs in that it commences at the middle of the parietals and forms a sharp angle.

Comparisons. Oligodon bivirgatus sp. nov. share similar scale patterns with O. ornatus , but differs from the latter by having different dorsal coloration (longitudinal stripes vs. crossbars in O. ornatus ), and ventral coloration (wide red band vs. narrow red line in O. ornatus ). The dorsal coloration of O. bivirgatus is also similar with O. pseudotaeniatus , but this new species can be distinguished from the latter by having 15/15/15 dorsal scale rows (vs. 17/17/ 15 in O. pseudotaeniatus ), a divided anal plate (vs. entire in O. pseudotaeniatus ), absence of a loreal (vs. present in O. pseudotaeniatus ), a larger count of 173–176 ventrals (vs. 137–156 in O. pseudotaeniatus ), and smaller count of 8 maxillary teeth (vs. 15 in O. pseudotaeniatus ). Additional morphological comparative data of Oligodon bivirgatus sp. nov. and 41 recognized Oligodon species occurred in mainland Southeast Asia are shown in Table 5.

By having 15/15/15 dorsal scale rows, Oligodon bivirgatus sp. nov. can be distinguished from its congeners occurring in mainland Southeast Asia having different numbers of MSR: O. albocinctus (19), O. annamensis (13), O. barroni (17), O. catenatus (13), O. cattienensis (17), O. chinensis (17), O. cinereus (17), O. condaoensis (17), O. cruentatus (17), O. culaochamensis (17 or 19), O. deuvei (17), O. eberhardti (13), O. fasciolatus (21 or 23), O. formosanus (19 or 17), O. joynsoni (17), O. lipipengi (19), O. macrurus (17), O. mcdougalli (13), O. melanozonatus (17), O. moricei (17), O. mouhoti (17), O. nagao (17 or 15), O. ocellatus (19), O. pallidocinctus (17), O. planiceps (13), O. saintgironsi (17 or 18), and O. taeniatus (19).

By having a divided nasal, Oligodon bivirgatus sp. nov. can be distinguished from its congeners occurring in mainland Southeast Asia having an entire nasal scale: O. catenatus , O. cattienensis , O. eberhardti , O. erythrorhachis , O. hamptoni , O. lacroixi , O. lungshenensis , O. melanozonatus , O. planiceps , and O. torquatus .

By having a divided anal plate, Oligodon bivirgatus sp. nov. can be distinguished from its congeners occurring in mainland Southeast Asia having an entire anal plate: O. albocinctus , O. annamensis , O. barroni , O. cattienensis , O. chinensis , O. cinereus , O. condaoensis , O. culaochamensis , O. deuvei , O. fasciolatus , O. formosanus , O. inornatus , O. joynsoni , O. kampucheaensis , O. lipipengi , O. macrurus , O. moricei , O. mouhoti , O. nagao , O. ocellatus , and O. pallidocinctus .

By the absence of a loreal, Oligodon bivirgatus sp. nov. can be distinguished from its congeners occurring in mainland Southeast Asia having one loreal or two: O. albocinctus , O. barroni , O. cattienensis , O. chinensis , O. cinereus , O. condaoensis , O. cruentatus , O. culaochamensis , O. deuvei , O. dorsalis , O. eberhardti , O. fasciolatus , O. formosanus , O. inornatus , O. jintakunei , O. joynsoni , O. kampucheaensis , O. lipipengi , O. melaneus , O. moricei , O. mouhoti , O. nagao , O. ocellatus , O. pallidocinctus , O. planiceps , O. saintgironsi , and O. torquatus .

By having eight maxillary teeth, Oligodon bivirgatus sp. nov. can be distinguished from its congeners occurred in mainland Southeast Asia having a larger or smaller number of maxillary teeth: O. albocinctus (10–12), O. barroni (10–13), O. chinensis (9–10), O. cinereus (10–12), O. condaoensis (11–13), O. cruentatus (14–16), O. culaochamensis (9–10), O. deuvei (12–15), O. fasciolatus (9–10), O. formosanus (10–11), O. inornatus (10–11), O. joynsoni (11–12), O. kampucheaensis (11), O. lipipengi (11), O. macrurus (13), O. melaneus (7), O. moricei (12), O. mouhoti (14–16), O. nagao (9–10), O. ocellatus (10), O. pallidocinctus (10–12), O. planiceps (10), O. pseudotaeniatus (15), O. rostralis (6), O. saintgironsi (10–12), O. taeniatus (14–17), and O. torquatus (15–16).

By having a dorsal coloration of longitudinal stripes, Oligodon bivirgatus sp. nov. differs from its congeners occurred in mainland Southeast Asia having a dorsal coloration of crossbars or blotches: O. albocinctus , O. annamensis , O. barroni , O. cattienensis , O. chinensis , O. culaochamensis , O. erythrorhachis , O. fasciolatus , O. formosanus , O. jintakunei , O. joynsoni , O. kampucheaensis , O. lipipengi , O. melanozonatus , O. nagao , O. ocellatus , O. pallidocinctus , O. rostralis , and O. saintgironsi .

Distribution and natural history. The new species is currently known only from Shangxi NR, Hainan, China. Both specimens were found at the same site in a stream of tropical lowland evergreen forest ( Figure 6A ). Snakes were observed about 19:30 hr–20:00 hr at night, so we believe that Oligodon bivirgatus sp. nov. is nocturnal. The paratype (SYNU 1808001) was found swimming in the slow stream, but crawled quickly when disturbed. The holotype (SYNU 1907027) was found on rock bank covered with moss along the stream ( Figure 6B ). O. bivirgatus sp. nov. are found to be sympatric with its congener O. formosanus , while the latter are larger in body size and more common in Shangxi NR. The other sympatric reptile species include Hebius boulengeri (Gressitt, 1937) , Bungarus multicinctus Blyth, 1861 , Trimerodytes percarinatus (Boulenger, 1899) , Goniurosaurus hainanensis Barbour, 1908 , Tropidophorus hainanus Smith, 1923 , Sphenomorphus incognitus (Thompson, 1912) and Sphenomorphus tonkinensis Nguyen, Schmitz, Nguyen, Orlov, Böhme and Ziegler, 2011 .

Figures

FIGURE 2. Type specimens of Oligodon bivirgatus sp. nov. in preservative. (A, B) Holotype SYNU 1907027; (C, D) Paratype SYNU 1808001. Photographed by Jingsong Shi and Shuo Qi. Scale bar equals 20 mm.

FIGURE 3. In life head scalation photos and drawings of Oligodon bivirgatus sp. nov. (Holotype SYNU 1907027, adult female). (A, D) Dorsal view; (B, E) Lateral view; (C, F) ventral view. Photographed and illustrated by Tianyu Qian. Scale bar equals 5 mm.

FIGURE 4. Oligodon bivirgatus sp. nov. in life (Holotype, SYNU 1907027), dorsal (A) and ventral (B) views. Images not to scale.

FIGURE 5. Three-dimensional CT reconstruction of the skull (A–C), lower jaw (D) and maxilla (E) of Oligodon bivirgatus sp. nov. (holotype, DOI: 10.12112/R.0001), implemented by Yemao Hou and Jingsong Shi. A–C, dorsal view, palatal view and lateral view of the skull; D, labial (d1) and lingual (d2, horizontal mirror) view of the lower jaw; E, lingual (e1) and dorsal (e2) view of the maxilla, double magnified.

FIGURE 6. Habitat of Oligodon bivirgatus sp. nov. in Shangxi Nature Reserve, Hainan, China. A: lowland evergreen forest; B: the microhabitat.