Oligodon mouhoti ( Boulenger, 1914 )

David, P., Vogel, G. & van Rooijen, J., 2008, A revision of the Oligodon taeniatus (Günther, 1861) group (Squamata: Colubridae), with the description of three new species from the Indochinese Region, Zootaxa 1965, pp. 1-49 : 23-28

Oligodon mouhoti ( Boulenger, 1914)

( Figs. 15–18)

Simotes [ taeniatus ] var. mouhoti Boulenger, 1914: 70 . – Type locality. Cambodia. Type locality not given in the original description; implicitly Cambodia because the description was based on the specimen depicted by Günther (1864: Pl. 20: Fig. A) that we have identified here. – Holotype, by present identification: BMNH RR 1946.1.3.32 (adult male), from Cambodia (see below). Collected by Henri Mouhot.

Material (25 specimens). – THAILAND. Bangkok Province and region. BMNH 78.2 .14.11 , BMNH 1969.1822 (2 males) , BMNH 63.9 .29.12 , BMNH 97.10 .8.27 , BMNH 1914.5 .11.7 , BMNH 1969.1834 – 1837 (7 females), “ Bangkok ” ; MNHN 1991.1817 (male) , MNHN 1991.1818 (female), “Bang-kok ( Siam)”, now Bangkok . Nakhon Ratchasima Province . BMNH 1969.1827 (male), “Korat”. Nakhon Sawan Province . BMNH 1969.1839 – 1840 (2 females), “Patnampo”, now Pat Namphau , just east of Nakhon Sawan . Phetchaburi Province . BMNH 1969.1833 (female), “ Petchaburi ”, now Phetchaburi ; IRSNB 16553 (male), Khao Nakwang, Nayang subdistrict, Cha-am District ; IRSNB 16554 (female) , MNHN 1999.7635 (male), Ban Salakern, Ban Lat District ; MNHN 1998.0572 (male), Ban Ton Kaet, Kaeng Krachan District . Prachuap Khiri Khan . BMNH 1969.1830 (male), “Huey Sak, Peninsular Siam ”, now Ban Huai Sak (or Ban Huai Sak Bon ) ; BMNH 1969.1832 (female), “Hua Hui”, most likely a lapsus from Hua Hin. No locality . BMNH 1969.1829 (female), “ Siam ” . – CAMBODIA. BMNH RR 1946.1.3.30–31 (2 males) , BMNH RR 1946.1 .3.32 (male; holotype), “ Cambodia ” .

Taxonomic comments. – The BMNH catalogue lists three syntypes for this species, BMNH RR 1946.1.3.30–32, all collected by H. Mouhot in “ Cambodia ”. However, the description of Boulenger (1914) was rather succinct. Boulenger understood the confusion created by Günther (1864), who had mixed specimens with 17 and 19 scale rows. As a consequence, Boulenger (p. 70) proposed a new name for specimens with 17 rows, as follows: “.... with 17 rows of scales and a blackish spot at the base of the tail and another at the end has been figured by Günther (Rept. Brit. Ind., pl. XX. Fig. A). (...) ... a new name (...) for the snake figured in the Reptiles of British India.” In so doing, Boulenger established the type of his description as the sole specimen depicted on Günther’s plate, which indeed has 17 rows and the black spots on the tail. The depicted specimen could have been selected only among four specimens: BMNH RR 1946.1.3.30–32, long regarded as the “ syntypes ”, collected by H. Mouhot in 1860–1861, and possibly another specimen with 17 rows available at Günther’s time, BMNH 1863.9.29.12, from “Bangkok”. A note added by Malcolm Smith at the end of Boulenger’s text (p. 70) mentioned the availability of 25 specimens of Simotes taeniatus var. mouhoti , but this note does not belong to Boulenger’s description and these specimens cannot be considered to be syntypes.

The drawing in Günther’s plate shows a specimen with a long tail and a single anterior temporal, which excludes the Bangkok specimen (a female with only 29 subcaudals) and BMNH RR 1946.1.3.30 (2 anterior temporals). According to the scalation data and head colour that can be determined from Günther’s plate, we identify without any ambiguity BMNH RR 1946.1.3.32 as the animal depicted on Günther’s plate. This specimens thus stands out as the holotype of Simotes [ taeniatus ] var. mouhoti Boulenger, 1914 .

Two other specimens with 19 dorsal scale rows collected by Henri Mouhot are referable to Oligodon taeniatus (see above). The confusion between Oligodon taeniatus and O. mouhoti has been discussed above.

Taylor (1965: 781) mentionned, under the name Oligodon taeniatus , specimens from Pattani Province and Songkhla Province, in southern Peninsular Thailand. We did not examine these specimens and we cannot assign them to any species. Nevertheless, the pattern as described by Taylor does not agree with that of Oligodon mouhoti .

Diagnosis. – A species of the genus Oligodon , characterized by: (1) an average size for the group, up to about 340 mm in total length; (2) deeply forked hemipenes, not spinose but bearing two large papillae; (3) 17 dorsal scale rows at midbody, 15 before vent; (4) 14–16 maxillary teeth, the last two strongly enlarged; (5) full complement of head scales, rarely including a presubocular; (6) 8 (rarely 7) supralabials; (7) anal plate single; (8) the presence of two dark longitudinal paravertebral stripes edging a pale (yellow in life) vertebral stripe, and two narrower dorsolateral stripes; (9) two large rounded, dark brown or black blotches on the upper surface of the tail, one at its base, the other one near the tip; (10) five major markings on upper head surface: one anterior across the snout, one small longitudinal, frontal marking, two central, oblique streaks directed posteriorly downwards, and one broad, arrow-shaped nuchal blotch; and (11) base of oblique central streaks reaching the ventral scales in all examined specimens.

Oligodon mouhoti differs from all other species of the group by the combination of (1) 17 scale rows at midbody, (2) the presence of a pattern similar to that of Oligodon taeniatus , namely two dark, conspicuous paravertebral and two dorsolateral stripes, and (3) two dorsal blotches on the upper surface of the tail, which are present in all examined specimens.

Campden-Main (1969) discussed the differences between O. taeniatus and O. mouhoti . This author rightly referred specimens with 19 DSR to O. taeniatus and those with 17 rows plus a pair of blotches on the upper tail surface to O. mouhoti . Campden-Main also noticed differences in the length of the oblique streaks behind the corner of the mouth. According to Campden-Main (1969), the lower end of each streak reaches ventral scales in O. mouhoti , whereas it stops short of ventrals in O. taeniatus . Our data do not agree fully with this statement. The streaks do reach a ventral scale in 55 out of 105 specimens (52.4% in O. taeniatus ). In O. mouhoti , the streaks reach a ventral scale in all examined specimens. This character should not be considered to be fully diagnostic to separate these two species.

Description and variation (based on Campden-Main [1969] and 25 examined specimens). – Morphology. Body rather elongated but not especially thin; head short, thick, barely distinct from the poorly defined neck; snout projecting forward of the lower jaw, long, amounting to 28.0–32.4 % (x = 29.5 %, s = 1.8) of HL, or 1.6–2.1 (x = 1.8, s = 0.2) times as long as diameter of eye; eye rather small, with a round pupil; tail rather short, thick, tapering.

Maximal total length known is 339 mm ( SVL 277 mm, TaL 62 mm) for a male ( BMNH 1969.1827 ). The largest examined female is 311 mm ( SVL 270 mm, TaL 41 mm; BMNH 1969.1833 ). In our sample, males reach a larger size than females. Ratio TaL/TL: 0.122 –0.185, with a strong sexual dimorphism (see below) .

Dentition. 14–16 maxillary teeth (x = 15.0, s = 0.7), the last two strongly enlarged and blade-like.

Body scalation. DSR: 17–17–15, without exception; scales small, ovoid, all smooth.

VEN: 145–163 (plus 1–2 preventrals), slightly angulate; SC: 29–43, paired (with a strong sexual dimorphism); anal plate entire.

Head scalation. Rostral thick, curved onto the upper snout surface, well visible from above, separating internasals by up to one half of their length; nasals subrectangular, about 1.6–2.0 times as long as high, vertically divided, with the posterior part distinctly smaller than anterior one; nostril crescentic, piercing middle of the nasal just forward of the division; internasals subrectangular, in broad contact, much shorter than prefrontals; prefrontals subrectangular, much wider than long; frontal hexagonal, ogive-like pointing backwards, 1.30–1.45 times as long as wide (x = 1.40, s = 0.05); an undivided supraocular on each side, much longer than wide, as wide as prefrontals; two very large, subtriangular parietals, much longer than the frontal, in broad contact; 1/1 small, elongate subrectangular loreal scale in 18 specimens, absent on both sides in 5 out of 23 specimens, and missing on one side of a sixth specimen, about 1.1–1.5 times as long as high, in broad contact with the nasal; 8/8 supralabials (7/ 7 in only 1/ 23 specimens), 1 st SL small, 2 nd and 3 rd in contact with loreal in all specimens, 4 th and 5 th entering orbit in all specimens, 6 th and 7 th largest; 1/1 preocular, high and narrow in all examined specimens; a small presubocular present (in 33/46 occurrences) or absent (13/46); 2/2 small postoculars in all examined specimens; 1/1 (in 44/ 46 specimens) or 2/2 (in 2/46) elongated anterior temporals, 2/ 2 posterior temporals; 9/9 (in 13/ 23 specimens), 9/10 (in 2/23) or 10/10 (in 8/23), first pair in contact, IL 1–4 (in 14/ 23 specimens) or 1–5 (9/23) in contact with anterior chin shields, 5 th IL the largest.

Colour and pattern in alcohol and in life. The upper surface is brownish-grey or greyish-tan, with dorsal scales finely edged with dark brown (same in life); from the nape up to the tip of the tail, a conspicuous yellow, tan or light brown vertebral stripe, wider than in O. taeniatus , edged on each of its side with a wider dark greyish-brown or tan blackish-brown paravertebral stripe (ochre brown in life); both paravertebral stripes are scattered or intersected with small black or dark brown irregular spots every 4 or 5 scales; an irregular dark brown stripe, narrower than paravertebral stripes, extends on each side on DSR 3–4 from the neck to the vent; these dorsolateral stripes are more or less regular or scattered with dark dots but are present in all specimens. The tail is similar to the upper body surface, with a wide and conspicuous vertebral stripe (not reaching tail tip), edged on each side with another diffuse brownish-grey stripe; two large, dark or blackish-brown vertebral blotches, more or less hexagonal or butterfly shaped, reaching down to the middle of the lateral surface of the tail; the first blotch is located at the level of subcaudals 1–5, its anterior tip reaching the level of the anal plate; the posterior blotch, much smaller than the anterior one, extends on 15–10 subcaudals before the tail tip; a faint, narrow dark brown lateral stripe on each side at the limit with subcaudals.

The head is brownish-grey or greyish-brown, darker than body; supralabials paler than upper head surface, cream more or less finely variegated with dark brown (same in life); five major markings above, as follows: a broad transversal dark brown marking on the snout (reddish-brown in life), just in front of eyes, extends downwards obliquely backwards across the eye down to SL 6–7; a short, narrow, arrow shaped, longitudinal streak on the frontal; on each side, a large, oblique dark brown or blackish-brown marking, not in contact on the top of the head, extends onto frontal, anterior part of parietals and posterior temporals, side of neck side behind corner of the mouth, then downwards, reaches in all examined specimens the corresponding ventral; lastly, a conspicuous, dark brown, heart-shaped, nuchal blotch, pointing forward with two short posterior branches in between which starts the vertebral stripe. Infralabials, chin and throat uniformly creamish-yellow or pale ochre brown; sometimes infralabials with a few dark brown spots.

The venter is creamish-yellow or greyish-yellow (cream anteriorly, then bright pink red or coral red in life), with, on most ventral scales, an irregular black subrectangular blotch near one or both tips; lower tail surface as venter, with subrectangular blotches in the anterior half of the tail, uniform behind.

Hemipenis (in situ). – The hemipenis is very similar to that of Oligodon taeniatus but longer; it is forked opposite the 7 th SC and reaches SC 18–19. On its proximal third it is covered with calyces and a few faint folds; the distal parts are smooth. The very long papillae, all smooth, are present as in O taeniatus .

Sexual dimorphism. – Clearly present in the three following characters: (1) difference in the ratio TaL/ TL: males: 0.172 –0.185 (x = 0.180, s = 0.004); females: 0.122 –0.131 (x = 0.127, s = 0.004); (2) difference in the number of ventrals: males: 145–152 (x = 148.0, s = 2.5); females: 154–163 (x = 157.8, s = 3.1); (3) difference in the number of subcaudals: males: 39–43 (x = 40.8, s = 1.1); females: 29–33 (x = 31.0, s = 1.4).

Distribution. – Thailand. Centre and east of the country, in provinces or region of Bangkok, Nakhon Ratchasima (Khorat), Nakhon Sawan (Pat Namphau, east of Nakhon Sawan), Phetchaburi (Ban Salakern, Ban Lat District; Ban Ton Kaet, Kaeng Krachan District; Khao Nakwang, Cha-am District; Phetchaburi, Muang District), and Prachuap Khiri Khan (Ban Huai Sak; Hua Hin) ( Taylor, 1965 [as O. taeniatus ]; Nabhitabhata et al., 2004 [as O. taeniatus ]; Pauwels et al., 2003; examined material). – Cambodia. No precise locality ( Saint Girons, 1972). Reading H. Mouhot (1864a –b) does not provide any clue because this naturalist travelled Cambodia from East to West.

As stated above, Taylor (1965: 781) mentioned specimens of “ Oligodon taeniatus ” from Pattani Province (Na Pradoo) and Songkhla Province (Songkhla), in southern Peninsular Thailand. These provinces were again listed by Nabhitabhata et al. (2004) in the account of O. taeniatus sensu Smith (1943) . On the basis of the short description of their pattern, these specimens do not agree with Oligodon mouhoti .

The occurrence of this species in Vietnam is questionable. It has been cited from this country only by Campden-Main (1970), from Thu Dau Mot, Province of Bình Duong, and by Nguyên et al. (2005), from Nam Dà, Province of Dak Nông. Campden-Main’s specimen could not be traced in the collections of the USNM (S. Gotte, pers. comm., 20 December 2007), but we received pictures of another Vietnamese specimen of “ O. mouhoti ”, USNM 166984 (Bien Hoa, Province of Dong Nai) that is actually a typical Oligodon deuvei spec. nov. (see below). Because there are only two, unverified records of Oligodon mouhoti in Vietnam, we delete for the present time this species from the snake fauna of this country.

Biology. – This small species is terrestrial, rather secretive and both diurnal and nocturnal. It is not uncommon. As far as is known, its biology is quite similar to Oligodon taeniatus . Taylor (1965: 780) collected specimens under piles of recently cut grasses. In Phetchaburi, specimen IRSNB 16553 was seen in mid afternoon on a sandy path near a rice field; specimen MNHN 1998.0572 was collected at night on a road in secondary forest. Two other specimens were caught inside a house, either by day (IRSNB 16554) or at night (MNHN 1999.7635) ( Pauwels et al., 2003). A wild caught specimen imported through the pet trade laid in a night of June 2005 two eggs, measuring 2.6 x 0.9 and 2.8 x 0.9 cm. The eggs were stuck together.

Discussion. – Oligodon mouhoti is the sole member of the group of O. taeniatus to display the twin blotches on the upper tail surface, these being present in all examined specimens. We came across other specimens with 17 dorsal scale rows but with a rather, often conspicuous vertebral stripe and usually no tail blotches. An analysis of their variation shows that they are referable to a distinct species, which we describe here as: