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Pareas geminatus DING, CHEN, SUWANNAPOOM, NGUYEN, POGARKOV & VOGEL, 2020

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Higher TaxaPareidae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
Subspecies 
Common NamesE: Twin Slug snake
Chinese: 伯仲钝头蛇 (Bó Zhòng Dùn Tóu Shé) 
SynonymPareas geminatus DING, CHEN, SUWANNAPOOM, NGUYEN, POGARKOV & VOGEL 2020
Pareas hamptoni — VOGEL 2010
Pareas hamptoni — TEYNIÉ & DAVID 2010 [partim]
Pareas geminatus — LIU & RAO 2021 
DistributionChina (Yunnan), Thailand (Chiang Mai), N Laos

Type locality: Jiangcheng County (21.207556° N, 94.020056°E; alt. 2,280 m elevation), Yunnan Province, China.  
Reproduction 
TypesHolotype. CIB118021, Adult male, collected by Ding Li on 21 May 2006.
Paratypes (n=5). Adult females, CIB118022 and CIB118023, collected from Jiangcheng County (22.603453 N, 101.882167 E; alt. 1,272 m a.s.l.), Yunnan Province, China; adult male, MNHN 0171S, collected from Houaphanh Province, Laos (no exact locality data); subadult male, ZMMU R-16695, collected from Long Tien, Xaisomboun Province, Laos; adult female, QSMI 1013, collected from Tak Province (approx. 16.425833 N, 99.000000 E; alt. 1,160 m a.s.l.), Thailand.
Other specimens: AUP 00176, ZMMU R-16477, ZMMU R-16478 (from Doi Inthanon NP, Chiang Mai Province, Thailand), KIZ 
DiagnosisDiagnosis. Pareas geminatus sp. nov. differs from all congeners by the combination of the following morphological characters: a slender, yellow-brown, medium-sized snake (total length 566 mm); one or two anterior temporals; loreal not contacting the eye; prefrontal contacting the eye; one preocular; slightly enlarged median vertebral row; usually 7 (6–8) supralabials; 8 infralabial scales; 3–5 scale rows slightly keeled at midbody; 170–188 ventrals lacking lateral keels; 75–91 subcaudals, all divided; slightly billowing vertical dark bars on the trunk; two slight thin black postorbital stripes starting from lower and upper edges of postorbital scales; lower postorbital stripe reaching the anterior part of seventh supralabial, not continuing to the lower jaw and chin; the left and right upper postorbital stripes merge forming a black nuchal collar.

Colouration. In preservative, dorsal surface head black, two black spots behind each eye and above the angle of the mouth respectively on each side of head; ventral surface of head uniformly yellowish. Dorsal surface body yellowish-brown, with about 56 dark faint bands and a few tiny black spots on each scale of the back; the black bands tapering downward on the sides of body and tail, sometimes crossing the vertebral; ventral surface body and tail pale with very sparse small black spots concentrating laterally, tail tip black.

Variation. Morphometric and meristic data for the type series are provided in Table 4 and Fig. 4. Paratypes generally agree with the holotype in scalation features. Some variation in body coloration is observed among specimens from China, Laos and Thailand. The topotype specimens from Jiangcheng County, Yunnan Province, China, vary in the degree of development of dark markings on dorsum, neck and dorsal surfaces: in some darker-colored specimens dark cross-bands on dorsum comprise two scales in width, and dark markings in nuchal area connect to dark brown spot covering almost all dorsal surfaces of the head (Fig. 4A), while in other specimens the dark patch on head abruptly terminates at the posterior edge of parietals, separated from much weaker nuchal dark markings by a light-orange collar (Fig. 4B). The adult male AUP-00176 is uniform reddish- brown dorsally, orange-yellow ventrally, with weak dark markings in nuchal area and on the dorsal surface of the head, and very weak almost indiscernible dorsal cross-bands (Fig. 4C). The characteristic dark postocular streaks are prominent in all specimens examined (Figs. 3, 4A–C) but the AUP-00176 (Fig. 4D). Iris reddish in life in all specimens.

Comparisons. Comparative morphological information of species considered to be diagnostic in the genus Pareas is summarized in Table 5. The new species is easily distinguishable from the P. margaritophorus group [including P. andersonii, P. margaritophorus, P. macularius, and P. modestus] by pale brown body coloration with bands (vs uniform dark grey or with bicoloured dots); from the P. carinatus group [including P. carinatus, P. nuchalis, and P. menglaensis] by the frontal scale shape subhexagonal with the lateral sides converging posteriorly (vs hexagonal with the lateral sides parallel), the anterior pair of chin shields longer than broad (vs broader than long), the prefrontal contacting eye (vs not in contact), and one or two anterior temporals (vs usually three); from P. monticola by the loreal not contacting the eye (vs usually contacting), the absence of a presubocular (vs present), 3–5 slightly keeled dorsal scale rows at midbody (vs all smooth), and the eye separated from the labials by a subocular scale (vs 4th or 4th–5th supralabials touching the eye); from P. boulengeri by the loreal not contacting the eye (vs usually contacting), 3–5 slightly keeled dorsal scale rows at midbody (vs usually all smooth), a single row of enlarged vertebral scales (vs vertebrals not enlarged), and a higher number of subcaudals 75–91 (vs 63–78); from P. chinensis by a single row of enlarged vertebral scales (vs 3 rows) and a higher number of subcaudals 75–91 (vs 69–76); from P. stanleyi by the loreal not contacting the eye (vs usually contacting), the supralabials not touching the eye (vs in contact with the eye), a lower number of keeled dorsal scales at midbody 3–5 (vs 13), a single row of enlarged vertebral scales (vs not enlarged), a higher number of ventrals 170–188 (vs 151–160), and a higher number of subcaudals 75–91 (vs 48–60).
Comparisons of Pareas geminatus sp. nov. with other members of the P. hamptoni group appear to be the most pertinent. The new species differs from P. atayal by 3–5 medial dorsal scale rows slightly keeled at midbody (vs 5–9 strongly keeled scales), a single row of enlarged vertebral scales (vs 3 rows), and the iris colour reddish (vs yellow); from P. iwasakii by 8 infralabials (vs 9–11) and a lower number of ventrals 170–188 (vs 189–194); from P. komaii by a lower number of keeled dorsal scales at midbody 3–5 (vs 9– 13), a single row of enlarged vertebral scales (vs 3 rows), and a higher number of subcaudals 75– 91 (vs 60–76); from P. mengziensis by the pale brown coloration of dorsum with indistinct darker crossbars (vs solid black marking on back of head extending to dorsum), a single row of enlarged vertebral scales (vs 3 rows), and a higher number of ventrals 170–188 (vs 167– 173); from P. nigriceps by a slightly higher number of subcaudals 75–91 (vs 73–77) and indistinct transverse bands on the body (vs distinct); from P. vindumi by the absence of a presubocular (vs presence), 7 supralabials (vs 6), a single row of enlarged vertebral scales (vs not enlarged), a higher number of subcaudals 75–91 (vs 61), and dark collar and cross bands on body present (vs absent); from P. formosensis by 3–5 dorsal scale rows at midbody keeled (vs all smooth) and a single row of enlarged vertebral scales (vs 3 rows); and finally from its sister species, P. hamptoni, by 3–5 dorsal scale rows at midbody slightly keeled (vs 5–9 scales strongly keeled), a lower number of ventrals 170–188 (vs 185–195) and a lower number of subcaudals 67–91 (vs 91–99).
Moreover, the new species differs from the two species described from northern Vietnam (Eberhardtia tonkinensis Angel, 1920, type locality: Tam Dao NP., Vinh Phuc Province, Vietnam) and from Hainan Is. of China (Amblycephalus carinatus hainanus Smith, 1923, type locality: Hainan) that are currently considered junior synonyms of P. hamptoni. Both of these species have completely smooth dorsal scale rows, which agrees with the diagnosis of P. formosensis and distinguishes them from the new species (3–5 slightly keeled dorsal scale rows at midbody in Pareas geminatus sp. nov.). As we demonstrate below, based on the analysis of topotypic material from northern Vietnam and Hainan, Eberhardtia tonkinensis Angel, 1920 and Amblycephalus carinatus hainanus Smith, 1923 have to be considered junior synonyms of P. formosensis. 
Comment 
EtymologyThe specific epithet “geminatus” is a Latin adjective in nominative singular (masculine gender) derived from the Latin “geminus”, for “twin”, “double”, and is given in reference to the similarity in morphology of the new species to its sister taxon, P. hamptoni, with which it was confused for a long time. 
References
  • Ding, Li; Zening Chen, Chatmongkon Suwannapoom, Tan Van Nguyen, Nikolay A. Poyarkov, & Gernot Vogel 2020. A new species of the Pareas hamptoni complex (Squamata: Serpentes: Pareidae) from the Golden Triangle. TAPROBANICA 9 (2): 174–193
  • Liu S, Rao D 2021. A new species of the genus Pareas (Squamata, Pareidae) from Yunnan, China. ZooKeys 1011: 121-138 - get paper here
  • Teynié, A. & David, P. 2010. Voyages Naturalistes au Laos: Les Reptiles. Éditions Revoir, Nohanent, 315 pp
  • Vogel, Gernot 2010. ON THE DISTRIBUTION OF Pareas hamptoni (BOULENGER, 1905) IN THAILAND (SERPENTES: PAREATINAE). Russ. J. Herpetol. 17 (3): 219 – 222 - get paper here
 
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