Subdoluseps vietnamensis, Le & Nguyen & Phan & Rujirawan & Aowphol & Vo & Murphy & Nguyen, 2021

Le, Manh Van, Nguyen, Vu Dang Hoang, Phan, Hoa Thi, Rujirawan, Attapol, Aowphol, Anchalee, Vo, Thi-Dieu-Hien, Murphy, Robert W. & Nguyen, Sang Ngoc, 2021, A new skink of the genus Subdoluseps Freitas, Datta-Roy, Karanth, Grismer & Siler, 2019 (Squamata: Scincidae) from southern Vietnam, Zootaxa 4952 (2), pp. 257-274 : 263-270

Subdoluseps vietnamensis sp. nov.

( Figs. 3 & 4 )

Holotype. ITBCZ 5842 , adult male, collected from Ho Tram Area , Xuyen Moc District, Ba Ria-Vung Tau Province, Vietnam; coordinates 10°29’38.2” N, 107°27’40.0” E; elevation 11 m asl by Sang N. Nguyen and Vu D.H. Nguyen, on 21 March 2017 ( Fig. 3 ).

Paratypes. Two adult males ITBCZ 5843 and 5844, and one adult female ITBCZ 5856 collected by Sang N. Nguyen and Vu D.H. Nguyen from the same site as the holotype; two adult males, ITBCZ 7038 and 7046, collected by Manh V. Le on 04 June 2020 at Ho Tram Area, Xuyen Moc District, Vietnam, coordinates 10°28’59.8” N, 107°26’03.6” E, elevation 10 m asl; two adult females ITCBZ 7056 and 7059, and one juvenile ITBCZ 7070 , collected by Manh V. Le on 04 June 2020 at La Gi Town , Binh Thuan Province, Vietnam, coordinates 10°42’38.8’’ N, 107°42’10.8” E, elevation 62 m asl ( Fig. 4 ) .

Diagnosis. Subdoluseps vietnamensis sp. nov. is distinguished from its congeners by a combination of the following morphological characters: medium size in adults (SVL up to 48.7 mm); tail length approximately equal to SVL; 27–30 smooth midbody scale rows; dorsal scales not enlarged; 55–57 paravertebral scales; 34–37 axilla-groin scales; 55–62 ventral scale rows; 64–74 subcaudal scales; four supraoculars; frontoparietal single; prefrontals not in contact with one another; two loreal scales; seven supralabials, the fifth below the center of the eye; one anterior and two posterior enlarged temporal scales; ear opening with two lobules on the anterior margin; 9 or 10 smooth subdigital lamellae beneath finger III and 12–15 beneath toe IV; six enlarged precloacal scales; and four distinct black stripes on dorsum.

Description of holotype. Adult male, SVL 46.5 mm; snout short and obtuse; lower eyelid scaly; body rather robust; tail regenerated. Head scales smooth; rostral convex, distinctly visible from above, broader than long (2.0 mm width, 1.0 mm height); a pair of supranasals forming short median suture, touching nasals and anterior loreals laterally, width equal to length (0.7 mm); prefrontals small, quadrangular, widely separated from each other, each touching both loreals; four supraoculars; frontal truncate anteriorly, longer than its distance from tip of snout, shorter than its distance from nuchal (2.0 mm vs. 3.2 mm), longer than wide (1.8 mm width, 2.6 mm length), touching two anterior supraoculars; frontoparietal single, much larger than interparietal, wider than long (3.0 mm width, 1.9 mm length), touching three supraoculars; parietals in contact posteriorly behind the interparietal; interparietal longer than wide (1.1 mm width, 1.6 mm length), with parietal eye visible posterior to center; a pair of nuchals; seven supralabials on both sides, fifth below center of the eye, first larger than the three following, sixth largest; two loreals, anterior (0.6 mm length, 0.6 mm height) slightly higher, the posterior (0.9 mm length, 0.5 mm height) longer; nasal divided, in contact with the first supralabial, rostral, anterior loreal, and supranasal; nostril in center of nasal; eight supraciliaries, first largest; one enlarged anterior temporal in contact with the sixth and the seventh supralabial; two posterior temporals, lower one smaller and overlapping the upper one, the lower temporal in contact with seventh supralabials; six infralabials, first two in contact with postmental; two pairs of chin shields, first pair medially in contact with each other; ear-opening moderately small, the anterior border with two lobules.

Body elongate (AGD/SVL = 0.56); dorsal scales smooth, not larger than lateral and ventral scales, with eight longitudinal rows on the back; 28 midbody scale rows; 71 paravertebral scales; 35 axilla-groin scales; ventral scales smooth, in 55 rows; limbs short (FLL/SVL = 0.18, HLL/SVL = 0.25), pentadactyl, widely separated by ten scales when adpressed; 3, 6, 9, 9, and 7 smooth lamellae beneath fingers I–V, respectively; 4, 7, 13, 13, and 9 smooth lamellae beneath toes I–V, respectively; six enlarged precloacal scales, the two middle ones slightly larger than the others; size of median subcaudal series on the original part of the tail equal to those of its adjacent rows.

Coloration. In life, overall dorsal coloration reddish brown with two dorsolateral bright lines on anterior part of dorsum; each dorsal scale of four central rows with a black spot forming four distinct longitudinal lines on dorsum; ear and surrounding area orange; sides dark brown to black intermixed with white, brown and yellow spots; chest and belly yellow ( Fig. 3 ). In preservation, color fades but the four longitudinal dorsal lines remain distinct; orange and yellow faded to cream or white; overall dorsal and lateral coloration black to dark brown with bright spots on lateral sides; venter cream.

Variation in paratypes (n = 8). Most morphological characters of paratypes agree with those of the holotype. The following main characters vary: (1) midbody scale rows: vary from 27 to 30; (2) paravertebral and ventral scale rows: range from 55 to 57 and from 55 to 62, respectively; (3) axilla-groin scales: range from 34 to 37; (4) and nuchals: range from one to three scales. Table 3 summarizes variation in size and scalation of the type series.

Field notes. All specimens were collected during the daytime, on sandy ground among rotting leaves in Earleaf acacia (Acacia auriculiformis A.Cunn. ex Benth.) plantation, secondary dipterocarp forest, and rubber plantation in lowland coastal areas ( Fig. 5 ). The holotype and paratypes ITBCZ 5843 & 5844 were collected at 15:42, air temperature 30.3 oC, relative humidity 70.2 %; ITCBZ 7038 was collected at 13:30, air temperature 33 oC, relative humidity 75 %; ITBCZ 7046 was collected at 8:54, air temperature 30 oC, relative humidity 80 %; ITBCZ 7056 , 7059 & 7070 were collected at 12:10, air temperature 32 oC, relative humidity 65%. To avoid capture, this species can dive into and stay under loose sand .

Sexual dimorphism. Adult males mainly differ from adult females in body coloration in life and shape of tail base. Males have yellow color on chest and belly (vs. white, cream or yellowish color in females), orange around the ear (vs. dark brown in females), and distinct bright spots on lateral side (vs. pure dark brown or with small bright dots in females). Ventral side of tail base is slightly swollen in males and flat in females ( Figs. 3 , 4A–E ). Juvenile has bright golden color on the dorsum with four clear dorsal longitudinal stripes ( Fig. 4F ).

Distribution. The new species is currently known only from (1) Ho Tram, Xuyen Moc District, Ba Ria-Vung Tau Province and (2) La Gi Town, Binh Thuan Province, southern Vietnam ( Fig. 1 ).

Etymology. The new skink is named after the nation of Vietnam. We recommend “ Vietnam Agile Skink” and “Thằn lằn chân ngắn việt nam” as the common English and Vietnamese names of the new species, respectively.

Comparisons. Subdoluseps vietnamensis sp. nov. differs morphologically from other species of the Lygosoma s.l. in Asia as follows: For Subdoluseps , S. vietnamensis sp. nov. differs from S. herberti , S. malayana , S. purthi , and S. samajaya by having a single frontoparietal scale (vs. paired) ( Grismer 2019; Karin et al. 2018; Sharma 1977; Smith 1916). In addition, it differs from S. herberti by having a smaller adult size (maximum SVL = 48.7 mm vs. 54.0 mm), presence (vs. absence) of nuchal scales (1–3 vs. 0), and smooth dorsal scales (vs. dorsal with 5 strong keels) ( Smith 1916); from S. malayana by having a smaller adult size (maximum SVL = 48.7 mm vs. 65.4 mm), more supralabials (7 vs. 6) with the fifth below the center of the eye (vs. the fourth below the center of the eye), smooth dorsal scales (vs. dorsal with 3–5 strong keels) ( Grismer et al. 2019); from S. purthi by having a smaller adult size (maximum SVL = 48.7 mm vs. 67.0 mm), fewer midbody scale rows (27–30 vs. 32–34), and more paravertebral scale rows (55–57 vs. 50) ( Sharma 1977); from S. samajaya by having a smaller adult size (maximum SVL = 48.7 mm vs. 70.1 mm), fewer paravertebral scale rows (55–57 vs. 60 or 61), and smooth dorsal scales (vs. dorsal with 5 strong keels) ( Karin et al. 2018).

Subdoluseps vietnamensis sp. nov. is phenotypically most similar to S. bowringii and S. frontoparietale but can be distinguished from both based on a combination of characters. The new species differs from S. bowringii by having a single frontoparietal scale (vs. paired) ( Geissler et al. 2011; Smith 1935; this study), tail length approximately equal to SVL (vs. tail longer than SVL) (mean TL/SVL = 1.04 vs. 1.27 [ Smith 1935; this study]), and fewer subcaudal scales (64–74 vs. 76–81) (this study); from S. frontoparietale by having a tail length approximately equal to SVL (mean TL/SVL = 1.04 vs. tail longer than SVL, mean TL/SVL = 1.24 [ Taylor 1962; this study, Table 4]), fewer subcaudal scales (64–74 vs. 78–80) [ Taylor 1962; this study]), fewer axilla-groin scales (34–37 vs. 39–42) (this study), four distinct longitudinal black stripes on dorsum (vs. six distinct black stripes) ( Taylor 1962; this study), and absence (vs. presence) of bright dorsolateral band extending from eye to tail base ( Taylor 1962; this study, Fig. 6 ).

From genus Lygosoma s.s., Subdoluseps vietnamensis sp. nov. differs from L. isodactylum , L. siamensis , L. tabonorum , and L. quadrupes (Linnaeus) by having supranasals in contact with each other (vs. not in contact) ( Geissler et al. 2011, Heitz et al. 2016, Siler et al. 2018) and from L. corpulentum by having smaller adult size (maximum SVL = 48.7 mm vs. 170.0 mm), frontoparietal scale single (vs. paired), and fewer midbody scale rows (27–30 vs. 36–40) ( Smith 1921; Geissler et al. 2011).

For the genus Riopa , Subdoluseps vietnamensis sp. nov. differs from R. albopunctata , R. anguinua , R. goaensis , R. guentheri , R. popae Shreve , and R. punctata (Gmelin) by having frontoparietal scales single (vs. paired) ( Geissler et al. 2012; Sharma 1976; Smith 1935); from R. lineata and R. lineolata by having fewer paravertebral scale rows (55–57 vs. 104–110 in R. lineata [ Smith 1935] and 78–93 in R. lineolata [ Siler et al. 2018]); and from R. vosmaeri by having hind-limb with 5 (vs. 4) toes (Gray 1939; Seetharamaraju et al. 2009).

For remaining Asian species of the Lygosoma s.l. that were not confirmed by Freitas et al. (2019), Subdoluseps vietnamensis sp. nov. differs from L. boehmei Ziegler, Schmitz, Heidrich, Vu & Nguyen , L. opisthorhodum Werner , L. singha (Taylor) , and L. veunsaiensis Geissler, Hartmann & Neang by having frontoparietal scale single (vs. paired) ( Geissler et al. 2012; Werner 1910; Ziegler et al. 2007); from L. angeli (Smith) by having a smaller adult size (maximum SVL = 48.7 mm vs. 100.0 mm) and fewer paravertebral scale rows (55–57 vs. 107–115) ( Smith 1937; Geissler et al. 2011); from L. haroldyoungi (Taylor) by having a smaller adult size (maximum SVL = 48.7 mm vs. 136.0 mm), fewer paravertebral scale rows (55–57 vs. 141–145), and fewer midbody scale rows (27–30 vs. 38–42) [ Taylor 1962; Geissler et al. 2011]; from L. kinabatanganensis Grismer, Quah, Duzulkafly & Yambun by having a smaller adult size (maximum SVL = 48.7 mm vs. 141.0 mm), fewer paravertebral scale rows (55–57 vs. 98), and fewer midbody scale rows (27–30 vs. 42) ( Grismer et al. 2018); from L. koratense Smith by having a smaller adult size (maximum SVL = 48.7 mm vs. 105.0 mm) and fewer midbody scale rows (27–30 vs. 32–34) [ Smith 1935]; and from L. bampfyldei Bartlett , L. peninsulare Grismer, Quah, Duzulkafly & Yambun , and L. schneideri Werner by having fewer paravertebral scale rows (55–57 vs. 81–85 in L. bampfyldei [ Grismer et al. 2018], 87 in L. peninsulare [ Grismer et al. 2018], and 95 in L. schneideri [ Grismer et al. 2018]).

Figures

FIGURE 1. Map showing the type localities of Subdoluseps vietnamensis sp. nov. (site 5) and S. frontoparietale (site 16) and other examined samples of S. bowringii. Vietnam: 1, Ngu Hanh Son District, Da Nang City; 2, Cu Lao Cham Island, Quang Nam Province; 3, Hon Ba, Khanh Hoa Province; 4, La Gi Town, Binh Thuan Province; 5, Ho Tram, Xuyen Moc District, Ba Ria- Vung Tau Province; 6, Nui Lon Mountain, Ba Ria-Vung Tau Province; 7, Con Dao Island, Ba Ria-Vung Tau Province; 8, Suoi Ngo, Tan Chau District, Tay Ninh Province; 9, Ba Den Mountain, Tay Ninh Province; 10, Lo Go-Xa Mat, Tay Ninh Province; 11, Hon Chong, Kien Giang Province; 12, Nam Du Island, Kien Giang Province; 13, Phu Quoc Island, Kien Giang Province; Cambodia: 14, Phnom Sruoch, Kampong Speu District, Khampong Speu Province; 15, Che Teal Chrum, Pursat Province; Thailand: and 16, Muak Lek District, Saraburi Province.

FIGURE 3. Holotype of Subdoluseps vietnamensis sp. nov., ITBCZ 5842.A, general view, in life (photo by Sang N. Nguyen); B&C, line drawing of lateral and dorsal views of head (drawn by Manh V. Le).

FIGURE 4. Paratypes of Subdoluseps vietnamensis sp. nov. in life. A, ITBCZ 5843, adult female (photo by Sang N. Nguyen); B, ITBCZ 7038, adult male; C, ITBCZ 7046, adult male; D, ITBCZ 7056, adult female; E, ITBCZ 7059, adult female; F, ITBCZ 7070, juvenile (photos by Manh V. Le).

FIGURE 5. Habitats of Subdoluseps vietnamensis sp. nov. from southern Vietnam. A&B, earleaf acacia plantation and dipterocarp forest on the sandy soil in Ho Tram area, Xuyen Moc District, Ba Ria-Vung Tau Province, respectively; C, rubber plantation in La Gi Town, Binh Thuan Province (Photos by Manh V. Le).

FIGURE 6. Examined specimens of Subdoluseps frontoparietale from its type locality in Thailand.A, Holotype FMNH 178262 (photo by Joshua Mata and Alan Resetar [Field Museum, Chicago, USA]); B, ZMKU R 00705; C, ZMKU R 00706, in life; D, ZMKU R 00707, juvenile (photos by Attapol Rujirawan).