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Pareas berdmorei THEOBALD, 1868

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Higher TaxaPareidae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes)
SubspeciesPareas berdmorei berdmorei THEOBALD 1868
Pareas berdmorei truongsonicus POYARKOV et al. 2022
Pareas berdmorei unicolor (BOURRET 1934) 
Common NamesE: Mengla Snail-eating Snake
Chinese: 勐腊钝头蛇 (Mengla Dun-tou-she) 
SynonymPareas berdmorei THEOBALD 1868
Pareas menglaensis WANG, CHE, LIU, KI, JIN, JIANG, SHI & GUO 2020

Pareas berdmorei unicolor (BOURRET 1934)
Amblycephalus carinatus unicolor BOURRET 1934
Pareas carinatus unicolor — NGUYEN et al. 2009
Pareas berdmorei unicolor — POYARKOV et al. 2022 
DistributionMyanmar, China, Vietnam, Laos, Thailand

Type locality: Mon State, Myanmar

menglaensis (invalid): China (Yunnan); Type locality: Mengla County, Yunnan Province, China, at an elevation of 700 m elevation.

truongsonicus: Laos: Type locality: Nahin District, Khammouan Province, Laos.

unicolor: Cambodia: Type locality: Kampong Speu Province, Cambodia.  
Reproduction 
TypesLectotype: ZSI 8022, adult male (Figs. 6C and 10 in Poyarkov et al. 2022): collected by T. M. Berdmore, designated by Poyarkov et al. 2022. Other specimens: ZSI.
Holotype. YBU 14124, adult female, collected in June 2014.
Paratypes. YBU 14141 and YBU 14142, two adult males from the same locality as the holotype but collected in July 2012 [menglaensis] 
DiagnosisDiagnosis: Pareas berdmorei differs from other members of the genus Pareas by the following combination of morphological characters: maximal total length of 770 mm; frontal scale hexagonal with its lateral sides parallel to the body axis; the anterior pair of chin shields broader than long; loreal and prefrontal not contacting the eye; generally 1 or 2 preoculars; regularly 2 (rarely 1 or 3) suboculars; generally single postocular (rarely 0 or 2); temporals 3 + 4 or 3 + 3; one to three median vertebral dorsal scale rows slightly enlarged; generally 8 (7–9) infralabials; 15 dorsal scale rows, of them 3–13 scale rows at midbody feebly keeled; 162–187 ventrals; 57–89 subcaudals, all divided; dorsum yellow-brown to orange, dark markings on dorsum variable; thin upper postorbital stripes continue to nape often forming elongated dark markings; iris uniform, color varies from beige to bright reddish-orange (Theobald, 1868b; Bourret, 1934; Taylor, 1965; Ziegler et al., 2006; Yang & Rao, 2008; Le et al., 2014; Pham & Nguyen, 2019; Wang et al., 2020; Poyarkov et al. 2022).

Body scalation. Dorsal scales in 15–15–15 rows, slightly keeled in 9 scale rows at midbody, lacking apical pits; vertebral scales in three median rows slightly enlarged; the outermost dorsal scale row not enlarged; ventrals 174 (+ 1 preventral), lacking lateral keels; subcaudals 64; cloacal plate single (Poyarkov et al. 2022).

Head scalation. Rostral not visible from above; single nasal; two internasals, much wider than long, narrowing and slightly curving back laterally (in dorsal view), anteriorly in contact with rostral, laterally in contact with nasal and loreal, posteriorly in contact with prefrontal, not contacting preocular; two large irregular pentagonal prefrontals, much larger than internasals and with a slightly diagonal suture between them, not in contact with eye; the frontal scale hexagonal with the lateral sides parallel to the body axis, longer than wide, smaller than parietals; two preoculars; one subocular; one postocular, not fused with subocular; one loreal in contact with prefrontal, not touching the eye; 7/7 supralabials, 3rd and 5th SL touching the subocular, none of them reaching the eye, 7th SL the largest, elongate; temporals 3 + 4; 8/8 infralabials, 3 pairs of chin shields interlaced, all notably broader than long, no mental groove under chin and throat; anterior chin shields relatively large (Poyarkov et al. 2022).

Coloration. Due to preservation in ethanol for over 150 years, the colors of the holotype have significantly faded, the specimen is uniform light brownish-yellow (Fig. 10A); the present body pattern of the lectotype no longer retains the original characteristics, though the thin dark postorbital stripes are still discernable and faded to orange-brown (Fig. 10B). In the original description, Theobald (1868b: 63) gives the following information on the type coloration: “color is uniform ochraceous, with obsolete traces of vertical bands down the body; two dark lines converge on the nape; <...> belly white”, indicating that the specimen has already significantly faded at the moment of the original description (Poyarkov et al. 2022).

Comparisons: Pareas berdmorei is distinguishable from P. carinatus by the generally larger body size (554.2 ± 76.5 mm vs. 494.3 ± 73.3 mm); by slightly higher number of ventrals (177.3 ± 5.8 vs. 171.4 ± 9.3); slightly higher number of keeled dorsal rows (9.0 ± 2.8 vs. 6.1 ± 3.3); by generally less pronounced dark markings in the nuchal area, thinner postorbital stripes and a more uniform coloration of the iris; from P. nuchalis by prefrontal not contacting the eye (vs. in contact); by the absence of the ring-shaped black blotch on the nape (vs. present); by lower number of ventrals (177.3 ± 5.8 vs. 209.9 ± 5.3); lower number of subcaudals (71.2 ± 7.5 vs. 111.1 ± 6.1); and by the presence of keeled dorsal scale rows (vs. dorsals totally smooth). Morphological comparisons between all species of the subgenus Pareas are detailed in Table 2 and Table S13. Pareas berdmorei can be distinguished from other species of Pareas belonging to subgenus Eberhardtia stat. nov. by having two or three distinct narrow suboculars (vs. one thin and elongated) and by having a hexagonal frontal with its lateral sides parallel to the body axis (vs. subhexagonal) (Tables S13 and S14). (Poyarkov et al. 2022).

Diagnosis (unicolor): Pareas berdmorei unicolor comb. nov. differs from other subspecies P. berdmorei by the following combination of morphological characteristics: body size medium to small (TL 459–576 mm); anterior pair of chin shields slightly longer than broad; loreal and prefrontal not contacting the eye; two (rarely one) suboculars; two (rarely one) postoculars; temporals generally 3 + 3 (rarely 3 + 4); three median vertebral scale rows slightly enlarged; 9 infralabial scales; 15 dorsal scale rows slightly keeled in 3–9 scale rows at midbody; 162–180 ventrals; 57–75 subcaudals, all divided; dorsum uniform yellow-ochre to bright orange lacking distinct dark vertebral spots and transverse dark bands (Figs. 13E and 13F); upper postorbital stripes generally absent or weakly discernable not contacting each other on the nuchal area; ventral scales yellowish to orange, generally immaculate, iris uniform bright orange-red (Figs. 13E and 13F). (Poyarkov et al. 2022).

Body scalation (unicolor). Dorsal scales in 15–15–15 rows, slightly keeled in seven scale rows at midbody, and without apical pits; three median vertebral scale rows slightly enlarged; the outermost dorsal scale row not enlarged; ventrals 164 (+ 2 preventrals), lacking lateral keels; subcaudals 64, all divided; cloacal plate single (Poyarkov et al. 2022).

Head scalation (unicolor). Rostral not visible from above; nasal entire; two internasals, much wider than long, narrowing and slightly curving back laterally (in dorsal view), anteriorly in contact with rostral, laterally in contact with nasal and loreal, posteriorly in contact with prefrontal, not contacting preocular; two large pentagonal prefrontals, much larger than internasals and with a slightly diagonal suture between them, not contacting the eye; single hexagonal frontal scale with its lateral sides parallel to the body axis, frontal longer than wide, smaller than parietals; two preoculars; one subocular; one postocular, not fused with subocular; one loreal in contact with prefrontal, not touching the eye; 7/7 supralabials, 3rd to 5th SL touching the subocular, none of them reaching the eye, 7th by SL the largest, elongate; temporals 3 + 3; 8/8 infralabials, the anterior most in contact with the opposite along midline, bordering mental, anterior 5 pairs of infralabials bordering anterior chin shields; 3 pairs of chin shields interlaced, no mental groove under chin and throat; anterior chin shields relatively large, slightly longer than broad, followed by the two pairs of chin shields that are much broader than long (Poyarkov et al. 2022).

Coloration (unicolor). Due to preservation in ethanol for almost a century, the color pattern has significantly faded; as the consequence the specimen no longer retains the original coloration characteristics. Presently the specimen is uniform dark reddish-brown with no pattern discernable on the ground color (Fig. 11). The original description contains the following information on the type specimen coloration: “the color is light reddish brown, absolutely uniform, without any spots on the body or head, yellower and lighter below” (Bourret, 1934: 15) (Poyarkov et al. 2022).

Comparisons (unicolor): Pareas berdmorei unicolor comb. nov. differs from P. b. berdmorei by slightly lower number of ventrals (162–180 [average 173.6 ± 5.1] vs. 166–186 [average 178.10 ± 5.19]), by generally lower number of keeled dorsal scale rows (3–9 [average 6.8 ± 1.9] vs. 5–13 [average 9.6 ± 2.2]), and by uniform orange to beige coloration lacking dark markings and transverse bands (vs. present) and brighter orange-red coloration of iris (vs. golden-bronze to orange). Pareas berdmorei unicolor comb. nov. differs from P. b. truongsonicus ssp. nov. described below by slightly smaller total length (459–576 mm [average 516.3 ± 42.5 mm] vs. 488–637 mm [average 587.0 ± 67.6]), by a lower number of ventrals (162–180 [average 173.6 ± 5.1] vs. 167–187 [average 179.5 ± 9.6]), by lower number of keeled dorsal scale rows (3–9 [average 6.8 ± 1.9] vs. 13), and by uniform orange to beige coloration lacking dark markings and transverse bands (vs. dark markings present) and brighter orange-red coloration of iris (vs. off-white to golden). For the detailed comparisons of the three subspecies of Pareas berdmorei see Table S12 (Poyarkov et al. 2022).

Diagnosis (truongsonicus): Pareas berdmorei truongsonicus ssp. nov. differs from other subspecies of P. berdmorei by the combination of the following morphological characters: maximal total length of 637 mm; anterior pair of chin shields as long as broad; loreal and prefrontal not contacting the eye; one subocular; one postocular; temporals 3 + 4; three median vertebral scale rows slightly enlarged; 9 infralabial scales; 15 dorsal scale rows keeled in 13 scale rows at midbody; 167–187 ventrals; 66–80 subcaudals, all divided; dorsum light brown with distinct dark-brown vertebral spots and 68–71 transverse dark bands, and with dense brownish-gray mottling covering dorsal, lateral and ventral surfaces of body and head (Figs. 13G–13H); upper postorbital stripes discernable, contacting each other on the nuchal area forming a clear Y-shaped pattern; ventral scales yellowish-white with dense brownish mottling, iris uniform off-white to golden (Figs. 13G–13H) (Poyarkov et al. 2022).

Body scalation (truongsonicus). Dorsal scales in 15–15–15 rows, the medial 13 scale rows slightly keeled at midbody, all dorsal scales lacking apical pits; three median vertebral scale rows enlarged; outermost dorsal scale row not enlarged; ventrals 187 (+ 1 preventral), all lacking lateral keels; subcaudals 66; cloacal plate single (Poyarkov et al. 2022).

Head scalation (truongsonicus). Rostral not visible from above; nasal single; internasals two, much wider than long, narrowing and slightly curving back laterally (in dorsal view), anteriorly in contact with rostral, laterally in contact with nasal and loreal, posteriorly in contact with prefrontal, not contacting preocular; two large irregular pentagonal prefrontals, much larger than internasals and with a slightly diagonal suture between them, not contacting the eye; the single frontal scale hexagonal with the lateral sides parallel to the body axis, longer than wide, smaller than parietals; one preocular; one subocular; one postocular, not fused with subocular; one loreal in contact with prefrontal, not touching the eye; 7/7 supralabials, 3rd to 5th SL touching the subocular, none of them reaching the eye, 7th SL the largest, elongate; temporals 3 + 4; 9/9 infralabials, the anterior most in contact
with the opposite along the midline, bordering mental, anterior 5 pairs of infralabials bordering the anterior chin shields; 3 pairs of chin shields interlaced, no mental groove under chin and throat; anterior chin shields relatively large, as long as broad, followed by two pairs of chin shields that are much broader than long (Poyarkov et al. 2022).

Coloration (truongsonicus). In life, dorsal surfaces of the head brownish with numerous marbled markings and dense brownish mottling (Fig. 13H). Head with two lateral postorbital stripes: the lower one is thick dark-brown line continuing from the middle of the eye onto the anterior part of the last supralabial; the upper one is a slightly thinner dark line running from postocular backwards to the dorsal scales on the neck (Fig. 12D). The upper postorbital stripes from the both sides of the body meet each other in the nape area forming a dark Y-shaped pattern (Fig. 13H). Lateral and ventral surfaces of the head marked with a dense brown dusting and larger dark spots (Figs. 12D and 12E). Dorsal surfaces light-brown with ca. 68 faint vertical dark brown bands. Ventral surfaces of the head, body and tail yellowish-cream with dense brown dusting. Iris uniform off-white, pupil black. In preservative: After two years of storage in ethanol the general coloration pattern has not changed (Fig. 12); yellowish tint in the coloration of dorsum, the head and eyes have faded becoming grayish-brown; other coloration features remain unchanged (Poyarkov et al. 2022).

Variation (truongsonicus): Measurements and scalation features of the subspecies Pareas berdmorei truongsonicus ssp. nov. (n = 4) are presented in Table S11. The two specimens examined in our study have a very similar coloration with the two specimens from Phong Nha-Ke Bang N. P. (ZFMK 82890 and VNUH 15.6.’05-1) reported by Ziegler et al. (2006); this population is geographically close (ca. 50 km direct distance; see Fig. 1C) to the loaclity of the new subspecies in Kim Hoa Commune, Tuyen Hoa District, Quang Binh Province. However, the members of the type series of the new subspecies have slightly lower number of ventral and subcaudal scales as compared to the specimens reported in Ziegler et al. (2006): VEN 187 vs. 167–177; SC 66–73 vs. 78–80. We also report on a population from Xe Pian N.P.A., Champasak Province, Laos (Fig. 1B) which agrees well with the specimens examined in our study in coloration (Fig. 13G); the morphological or genetic data on this population is lacking. Therefore, in this study we tentatively assign the specimens from Phong Nha-Ke Bang N.P. and from Xe Pian N.P.A. to P. cf. b. truongsonicus ssp. nov.; the taxonomic status of this population has to be clarified in the future (Poyarkov et al. 2022).

Comparisons (truongsonicus): In our sample of four specimens Pareas berdmorei truongsonicus ssp. nov. differs from P. b. berdmorei by slightly higher of number of ventrals (187 vs. 166–186 [178.10 ± 5.19]), by slightly higher number of keeled dorsal scale rows (13 vs. 5–13 [9.60 ± 2.20]); by the dense brownish mottling and bigger brown spots on dorsal, lateral, and ventral surfaces of the head and body (vs. ventral surfaces immaculate, lateral and dorsal surfaces with sparse dusting); and by uniform off-white to golden color of iris (vs. golden-bronze to orange). The new subspecies differs from P. b. unicolor comb. nov. by slightly larger maximal total length (622–637 mm vs. 459–576 mm [516.3 ± 42.5 mm]), by a generally higher number of ventrals (187 vs. 162–180 [173.6 ± 5.1]), by a higher of number keeled dorsal scale rows (13 vs. 3–9 [6. 8 ± 1.9]); by the presence of dark markings on dorsum and ventral surfaces, including the dark transverse bands and brownish mottling (vs. uniform orange to beige coloration lacking dark markings), and by off-white to golden coloration of iris (vs. bright orange-red color of iris). Detailed comparisons of the three subspecies of Pareas berdmorei are presented in Table S12 (Poyarkov et al. 2022).

Diagnosis (menglaensis). (1) prefrontal separating from orbit; (2) three chin-shield pairs, anterior pair smaller than other two; (3) 9–13 rows of mid dorsal scales keeled; (4) three rows of mid dorsal scales enlarged; (5) single loreal, not bordering orbit; (6) two preoculars, 2–3 suboculars, single postocular; (7) 9–11 temporals (3+3+3, 3+4+4, or 3+4+3); (8) seven supralabials, not bordering orbit; (9) 7–8 infralabials; (10) 3–5 maxillary teeth; (11) cloaca undivided; (12) dorsal scales in 15 rows throughout; (13) 176–177 ventral scales; (14) 65–79 subcaudals, paired (Wang et al. 2020).

Comparison (menglaensis). Pareas menglaensis sp. nov. can be distinguished from P. carinatus by 11 rows of dorsal scales strongly keeled at mid-body (vs. 3–5 rows feebly keeled), from P. nuchalis by prefrontal separated from orbit (vs. prefrontal bordering orbit), and from all other species of Pareas by two or three distinct narrow suboculars (vs. one thin elongated subocular) (Wang et al. 2020). 
CommentSynonymy: Poyarkov et al. 2022 revalidated P. bermorei from the synonymy of P. carinatus and synonymized P. Pareas menglaensis with P. berdmorei.

Distribution: see map in Poyarkov et al. 2022: Fig. 1. 
EtymologyTheobald (1868b) named his new species in honor of British naturalist Captain Thomas Matthew Berdmore (1811–1859), who was the collector of the type specimens.

The new subspecies name “truongsonicus” is a Latin toponymic adjective in nominative singular, adopting the masculine gender of the genus name Pareas, and is given in reference to the Truong Son (Annamite) Mountain Range in Vietnam and Laos, where the new subspecies occurs (Poyarkov et al. 2022).

P. menglaensis was named after the type locality, Mengla County, Yunnan, China. 
References
  • Poyarkov NA, Nguyen TV, Pawangkhanant P, Yushchenko PV, Brakels P, Nguyen LH, Nguyen HN, Suwannapoom C, Orlov N, Vogel G. 2022. An integrative taxonomic revision of slug-eating snakes (Squamata: Pareidae: Pareineae) reveals unprecedented diversity in Indochina. PeerJ 10: e12713 - get paper here
  • Wang P, Che J, Liu Q, Li K, Jin JQ, Jiang K, Shi L, Guo P 2020. A revised taxonomy of Asian snail-eating snakes Pareas (Squamata, Pareidae): evidence from morphological comparison and molecular phylogeny. ZooKeys 939: 45-64 - get paper here
 
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