Scincella balluca, Bragin & Zenin & Le & Nguyen & Nguyen & Bobrov & Poyarkov, 2025

Bragin, Andrey M., Zenin, Evgeniy S., Le, Son Xuan, Nguyen, Duc Trung, Nguyen, Tan Van, Bobrov, Vladimir V. & Poyarkov, Nikolay A., 2025, Gold of the highlands: a new ground skink (Reptilia: Squamata: Scincidae: Scincella Mittleman, 1950) from southern Vietnam, Zootaxa 5701 (3), pp. 247-291 : 272-282

Scincella balluca sp. nov.

urn:lsid:zoobank.org:act:

( Figs 3–6 ; Table 3 )

Chresonymy:

Scincella cf. doriae — Poyarkov & Vassilieva (2011: 219, in part).

Scincella doriae (non Lygosoma doriae Boulenger, 1887 )— Neang et al. (2018: 225; in part); Poyarkov et al. (2023: in part); Jia et al. (2024: 117, in part); Pham et al. (2024: 94, in part); Bragin et al. 2025 (201: in part); Jia et al. (2025:1-22, in part; Pham et al. (2025: 325, in part); Nguyen et al. (2025: 271, in part).

Holotype. ZMMU Re-18292 (field no. NAP-15389), adult male, from Ta Dung Mountain within Ta Dung National Park , Dak P’Lao Commune, Bich Khe District, Dak Nong Province, southern Vietnam ( 11.85029°N, 108.02750°E; elevation 1,880 m asl) collected by N.A. Poyarkov and A.M. Bragin on 24 January 2021 .

Paratypes (n = 8). Eight specimens collected from the same locality and with the same collection information as the holotype: five adult males VRTC NAP15328 (field no. NAP-15328), VRTC NAP15329 (field no. NAP-15329), VRTC NAP15330 (field no. NAP-15330), ZMMU Re-18293 (field no. NAP-15331), and VRTC NAP15390 (field no. NAP-15390) ; and three adult females ZMMU Re-18294 (field no. NAP-15321), VRTC NAP15386 (field no. NAP-15386), and ZMMU Re-18295 (field no. NAP-15391) .

Referred materials (n = 24). Nine individuals from Ta Dung Mt., within Ta Dung NP, Dak P’Lao Commune, Bich Khe District, Dak Nong Province, Vietnam ( 11.85029°N, 108.02750°E; elevation 1,880 m asl): VRTC NAP15315 (field no. NAP-15315), VRTC NAP15323–NAP15327 (field nos. NAP-15323 to NAP-15327), VRTC NAP15387 (field no. NAP-15387), VRTC NAP15388 (field no. NAP-15388), and ZMMU NAP15322 (field no. NAP-15322), collected by A.M. Bragin on 7 November 2023; and ZMMU NAP10375 (field no. NAP-10375), ZMMU NAP10488 (field no. NAP-10488), and ZMMU NAP10490 (field no. NAP-10490), collected by N.A. Poyarkov on 24 January 2021. One specimen from Chu Yang Sin Mt., Chu Yang Sin NP, Bong Krang Commune, Lak District, Dak Lak Province, Vietnam ( 12.37935°N, 108.35373°E; elevation 1,710 m asl): VRTC NAP15966 (field no. NAP-15966), and ZMMU NAP02712 (field no. NAP-02712), collected by N.A. Poyarkov on 13 April 2012. 14 specimens from Bidoup Mt. within Bidoup-Nui Ba NP, Lac Duong District, Lam Dong Province,( 12.08000°N, 108.66000°E), collected by N.A. Poyarkov in June 2009: ZMMU Re-13268-NAP00505 (field no. NAP-00505), ZMMU Re-13268-NAP00412 (field no. NAP-00412), and ZMMU Re-13268-NAP01062 (field no. NAP-01062); collected by N.A. Poyarkov in June 2012: ZMMU NAP01419 (field no. NAP-01419), ZMMU NAP01421 (field no. NAP-01421), ZMMU NAP01420 (field no. NAP-01420), ZMMU NAP01331 (field no. NAP-01331), ZMMU NAP01332 (field no. NAP-01332), ZMMU NAP01328 (field no. NAP-01328), and ZMMU NAP01329 (field no. NAP-01329); collected by N.A. Poyarkov in July 2012: ZMMU NAP01715 (field no. NAP-01715), ZMMU NAP01706 (field no. NAP-01706), ZMMU NAP01719 (field no. NAP-01719), and ZMMU NAP01743 (field no. NAP-01743); collected on 3 July 2022: ZMMU NAP12551 (field no. NAP-12551).

Diagnosis. Scincella balluca sp. nov. is distinguished from all other congeners by the following unique combination of morphological characters: (1) slender, medium-sized body, snout-vent length 46.1–57.9 mm; (2) prefrontals generally separated from each other (rarely in contact); (3) infralabials seven; (4) superciliaries seven (rarely eight); (5) two preoculars, two presuboculars, two postoculars, three postsuboculars (rarely four or five postsuboculars); (6) enlarged nuchals absent; (7) supralabials separated from the eye by a row of small scales; (8) tympanum deeply sunk without projecting lobules; (9) midbody scale rows 32 (rarely 30); (10) dorsal scales smooth, slightly enlarged, with 62–66 paravertebral scale rows; (11) 60–67 ventral scale rows (including gulars); (12) upper edge of the dorsolateral longitudinal stripes relatively straight, with six rows of dorsal scales in the middle; (13) enlarged, undivided lamellae beneath finger IV 10–12; (14) enlarged, undivided lamellae beneath toe IV 18–20; (15) two enlarged precloacal scales; (16) dorsal surface of body brown with sparsely scattered irregular black spots; (17) ventral surface of throat, belly, and base of tail golden yellow; (18) hemipenes bilobed with two asymmetrical lobes, longer lobe with regular transverse grooves and with terminal papillae.

Etymology. The specific epithet of the new species is formed from the Latin noun “ ballux,” meaning “grain of gold.” This name is given in reference to the golden coloration of the flanks and the ventral surface of the body in the new species, as well as the glossy surface of the scales, which occasionally shimmer in the sunlight. We propose the following common names for this species: “Golden Ground Skink” in English, “Thằn lằn ánh vàng” in Vietnamese, and “Zolotistyi malyi stsink” (“Золотистый малый сцинк”) in Russian.

Description of the holotype ( Figs. 3–6 ). The holotype is an adult male in a good state of preservation with a 30 mm long mid-ventral incision. The hemipenes of the specimen are partially everted to determine the sex of the specimen and for description. The specimen is preserved in a linear manner (SVL 55.4 mm; TaL 93.3 mm; total length 148.7 mm); snout rounded and acute in dorsal and lateral aspects (EED/END 1.7); nostril with lateral orientation, slightly oval, posterior edge oriented diagonally upward, situated much closer to the snout tip than to the eye (END/SNL 0.75) in the middle of the nasal; head robust, longer than wide (HL2/HW 1.4). Body slender (MBW/SVL 0.17); head widened posteriorly; the border between head and neck and cervical interception in front of the attachment point of forelimbs are poorly visible. Forelimbs and hindlimbs relatively short and stout (FLL/ SVL 0.24; HLL/SVL 0.36), normally developed, each with five digits; tips of digits of adpressed forelimbs and hindlimbs do not meet; adpressed forelimbs do not reach eye; tibia relatively short (TBL 5.1 mm; TBL/SVL 0.09), shorter than femur (FML 6.1 mm; TBL/FML ratio 0.83) ( Fig. 4 H, I ). Digits moderately long, slender, and ending with distinctly visible, sharp, thin, slightly curved, and pointed claws. Subdigital lamellae on manus and pes slightly convex, rounded, and entire; the number of subdigital lamellae (without taking into account claw sheaths): right manus 7–8–10–12–8; right pes 7–9–15–20–12. Relative lengths of digits: left manus IV> III> V> II> I; left pes IV> III> V> II> I. Scales on dorsal and ventral surfaces of the limbs are smooth and imbricate; femoral scales are large with longitudinal orientation. Scales on palmar and plantar regions are a little bit larger than the associated subdigital lamellae and much smaller than scales on ventral surfaces of limbs; rounded, smooth, and slightly convex ( Fig. 4 D, E ). Other measurements and ratios of the holotype are given in Table 3 .

Rostral wider ( 1.7 mm) than long ( 1 mm), in contact with first supralabials, nasals, and frontonasal ( Figs. 4 B, C ; 5 A, B ). A pair of nasals not in contact with each other. Nasal posteriorly in contact with slightly smaller anterior loreal; laterally widely in contact with first supralabial. A large single frontonasal in broad contact with rostral anteriorly and frontal posteriorly; widely in contact with nasals, anterior loreals, and prefrontal laterally. A pair of prefrontals separated by frontal. Prefrontal anteriorly in contact with frontonasal, posteriorly in contact with frontal, first supraocular, and first enlarged superciliaries, and laterally in contact with anterior and posterior loreals. Frontal large, nearly twice longer than wide, irregularly pentagonal with slightly rounded tapering posterior margin, contacting frontonasal and prefrontals anteriorly, in wide contact with first and second supraoculars laterally, and in wide contact with frontoparietals posteriorly. Frontoparietals widely in contact with parietals and interparietal scale posteriorly, contacting frontal and second, third, and fourth supraoculars anterolaterally. Interparietal rhomboid, posteriorly in contact with parietals; parietal eye clearly visible. Parietal anteriorly in contact with frontoparietal, interparietal, and in slight contact with fourth supraocular; laterally touching upper secondary temporal and upper and lower pretemporals; in contact with three (right parietal) and two (left parietal) paravertebral scales posteriorly. Parietal overlapping upper secondary temporal. Enlarged nuchals absent ( Figs. 4 B, C ; 5 A, B ).

Four supraoculars, the second being the largest, decreasing in size in both directions. Scales on the lateral aspect of the head bearing small pits, scattered all over their surface ( Fig. 4 С). Nostrils with lateral orientation, slightly oval, posterior edge oriented diagonally upward, located in the middle of nasal. Nasal undivided. Postnasals absent. Anterior loreal roughly triangular, and posterior loreal roughly quadrangular, with posterior loreal wider than anterior loreal; anterior loreal anteriorly in contact with nasal and frontonasal, posteriorly in contact with posterior loreal and prefrontal, and laterally in contact with second supralabial. Posterior loreal anteriorly in contact with anterior loreal and prefrontal, posteriorly in contact with first enlarged superciliaries and two preoculars, and laterally in contact with second and slightly touching third supralabials. Two preoculars, the upper one smaller than the lower one; two presuboculars. Anterior presubocular located between lower preocular, the upper edges of third and fourth supralabials, and posterior presubocular, on the upper edge bordered by a row of small scales separating it from the eye. Posterior presubocular located between anterior presubocular and the upper edges of fourth and fifth supralabials, separated from postsuboculars by a row of two small scales. The upper eyelid bordered by seven superciliaries and nine ciliary scales; superciliary and ciliary rows not broken.An enlarged scale located between the first two superciliaries, upper preocular, and the first two ciliary scales. Lower eyelid with fourteen ciliary scales; the scales covering lower eyelid small, slightly quadrangular, tightly adjacent, non-overlapping. Lower eyelid bearing elongated rectangular, horizontally oriented transparent window (PDD 0.6 mm). The upper edge of the transparent window is separated by one row of small eyelid scales from the lower edge of ciliaries. Seven supralabials, gradually increasing in size, with the sixth supralabial being the largest; fifth supralabial located below the center of the eye; while fourth, fifth, and sixth supralabials separated from the lower edge of the eye by presuboculars, postsuboculars, and a row of small scales. Two postoculars; upper one three times larger than lower one, anteriorly in contact with the last superciliar and last supraocular, posteriorly in contact with upper pretemporal, and laterally in contact with lower postocular and last ciliary scale; lower postocular anteriorly in contact with upper one and the small scales, separating it from eyelid, posteriorly in contact with upper and lower pretemporals, and laterally in contact with upper postsubocular. Three postsuboculars, where the upper one is the smallest, posteriorly in contact with lower pretemporal, laterally in contact with middle postsubocular; middle postsubocular in contact with lower pretemporal and primary temporal posteriorly and with lower postsubocular laterally; lower postsubocular located between the upper edges of fifth and sixth supralabials, middle postsuboculars, and a row of small scales under lower eyelid. One large rhomboid primary temporal anteriorly in contact with lower pretemporal, two postsuboculars and sixth supralabial, posteriorly in contact with upper and lower secondary temporals, and seventh supralabial. Two secondary temporals, the upper one is larger than the lower one. Parietal and lower secondary temporal overlap with upper secondary temporal. Secondary temporals anteriorly in contact with parietal, lower pretemporal, primary temporal and seventh supralabial, posteriorly in contact with, upper and lower tertiary temporals and upper postsupralabial. Two equal-sized elongated postsupralabials posteriorly to the seventh supralabial. Four scale rows separate postsupralabials and the anterior edge of the ear opening. Ear opening large, tympanum deeply sunk, not covered with scales, with no projecting ear lobule on the anterior edge of ear opening ( Fig. 4 B, C ; 5 A, B ).

Six infralabials, of which the fifth being the largest. Mental scale wider than longer, its posterior margin concave. Anterior postmental single, large, nearly three times the length of mental, laterally postmental widely in contact with first and second infralabials on both sides. The first pair of chinshields medially contact each other, laterally in contact with the second and the third infralabials. The second pair of chinshields in contact with the fourth infralabials and slightly in touch with the third infralabials, separated by one subequal rhomboid gular scale. The third pair of chinshields touching the fourth and widely in contact with the fifth infralabials, separated by three subequal rhomboid gular scales ( Figs. 4 A ; 5 C ).

Dorsal scales imbricate, smooth, and glossy. Scalation predominantly homogeneous, although the vertebral scales are slightly enlarged and broader than smaller cycloid scales on flanks, starting downwards from the dorsolateral stripes. Enlarged nuchals absent. Six full and half on each side midbody dorsal scale rows (0.5–6–0.5) located between dark dorsolateral stripes. The paravertebral scale series is composed of 63 scales. Scales around the midbody in 32 rows. Scales on lateral surface of neck and limbs much smaller and more or less similar in shape to those on body flanks. Midventral scale series composed of 62 scales when counted from the first pair of chinshields (including gulars) to precloacal scales. Medial pair of precloacal scales enlarged; left enlarged precloacal overlapped right one; two enlarged precloacals overlapped outer smaller scales. Tail complete; tail scales smooth, imbricate; all equal in shape except subcaudals, which are slightly widened (one and a half times larger than scales of vertebral row) ( Figs. 4 H, I ; 5 ).

The hemipenes ( Fig. 4 F, G ) are deeply forked with two asymmetrical lobes. The outer lobe is three times longer than the inner lobe. Lobes well-developed, rounded, with lateral orientation. When fully everted, the long lobe curves forward and outward before rounding inward. The long lobe slightly widens towards the apex. The body of the longer lobe has regular transverse grooves on the dorsolateral surface, which are shallow and rounded at the top, and ends with low, huddled terminal papillae (according to Nguyen et al. (2018); or unpaired terminal awl (according to Vergilov et al. (2017), and Vergilov & Zlatkov (2024)). Other calcified structures, ornamentation, and cup-shaped or spiny structures on lobes and truncus surface absent. The truncus slightly widens from its base to the bifurcation point. Sulcus spermaticus directed ventrally, narrow, poorly visible, and covered by folds of truncus and lobes. The folds of the lobes exhibit prominent fleshy extensions surrounding the sulcus openings at the tips of each hemipenial branch. Total length of hemipenis (from the base to the top of the longer lobe): 8.0 mm; length of truncus: 2.2 mm; length of the long lobe: 5.8 mm; length of the short lobe: 1.9 mm; width of the long lobe at the narrowest point: 1.0 mm; width of the long lobe at the widest point: 1.7 mm; width of the short lobe: 1.3 mm; width of truncus in its middle point: 1.4 mm.

Coloration in life ( Fig. 3 ). The dorsal surface of the body is dark brown with irregularly scattered black spots, more concentrated on the sides. The dorsal scales have a golden olive border along the lateral edges. The head is slightly darker, with fine scattered dark speckling extending from the snout to the nape. The limbs are yellowbrown, densely covered with deep brown speckles. The dorsolateral stripe starts at the snout, passing over the nasal and loreals, is interrupted at the eye, and continues immediately behind it, running along the flanks above the limbs and extending to the base and a little further along the tail, where it abruptly ends. The dorsolateral stripe is black, narrow, approximately two to three scales wide, and lacks white spots but has rare golden strokes and spots; along the dorsal edge there is a golden border the width of half a scale; the lower edge is framed by the golden yellow coloring of the flanks. On the flanks, closer to the lower edge, the dark coloration changes to bright golden yellow, forming a gradient rather than a sharp border. The flanks have large black spots, ending on the belly. The ventral surface of the body is bright golden-yellow, most intense on the throat and belly, extending to two-thirds of the tail. The limbs have the same golden yellow color on the ventral surface. The ventral surface of the head and the last third of the tail are yellowish-white and grayish-white with scattered dark speckles along the margins of the chinshields and the edges of the ventral tail scales; the ventral surface of the palms and feet is yellowish gray-olive.

Coloration in preservative ( Fig. 4 ).After four years in ethanol, the dorsal surfaces faded to dark grayish-brown, with the golden-brown speckling becoming less distinct. The dorsolateral stripes remain well-defined but appear darker and more contrasting against the paler body. The stripe also acquired a subtle, contrasting light border along its upper edge. The head scales darkened significantly, with the original fine speckling becoming more prominent, especially on the sides of the ventral surface. The parietal eye became more visible. The limbs, previously yellowbrown, now appear dull brown with less contrast between the speckles and the background coloration. The flanks and venter lost their bright lemon-yellow hue, becoming pale, almost whitish tone with a faint grayish hue. The flanks and ventral surface of the head, neck, trunk, and tail faded to an off-white or light gray. Black spots on the ventral surfaces of the head, neck, and tail became more contrasting. The palmar surfaces of the forelimbs and hindlimbs, fingers, and toes became pale gray, and the contrast between dorsal and ventral coloration is reduced.

Variation. The paratypes are similar to the holotype in most morphometric and meristic characters, with the following character variations: (1) PVSR and VSR: 62–66 and 60–67, respectively; (2) MBSR from 30 to 32; (3) the prefrontals are generally separated, rarely touching each other; (4) superciliaries generally seven, but in ZMMU Re-18295—eight; (5) postsuboculars generally three, but in VRTC NAP15329 posterior postsubocular, in ZMMU Re-18293 middle postsubocular, and in ZMMU Re-18294 posterior and middle postsuboculars are divided into two smaller scales, increasing the total number of postsuboculars to four in VRTC NAP15329 and ZMMU Re-18293 and to five in ZMMU Re-18294; (6) ciliars from 9 to 12; (7) FL4 and TL4: 10–12 and 18–20, respectively.Although there are no sexual differences in coloration, males are generally larger (SVL), have greater absolute tail length (TaL/SVL), proportionally longer (HL1, 2), broader (HW), and more robust (HD) heads, relatively wider (MBD) bodies, slightly larger eyes (ED) and tympana (TD), and longer forelimbs (FLL) and hindlimbs (HLL) than females. Other minor variations are summarized in Table 3 .

There is no sexual dimorphism in coloration. In juveniles, the golden yellow coloration of the body is not expressed. Only the belly is golden, but not as bright as in adults, and the golden yellow coloration of the sides of the body is represented by separate golden spots on a dark brown background, more intense in the area of the acetabulum and groin cavities.

Comparisons. Scincella balluca sp. nov. can be readily distinguished morphologically from other congeners from Indochina; the diagnostic characters are summarized in Tables 4–5 .

In our phylogenetic analysis, Scincella balluca sp. nov. is closely related to S. baraensis , from which it can be distinguished by a fewer number of dorsal scale rows between the dorsolateral stripes (6 vs. 8), fewer paravertebral scale rows (62–66 vs. 66–70), and by the absence of nuchals (vs. present), and the absence of projecting ear lobules (vs. present).

The new species was previously confused with S. doriae (originally described from northern Myanmar) in two published records from Bidoup-Nui Ba NP ( Poyarkov & Vassilieva 2011; Neang et al. 2018). However, the new species can be readily distinguished from the latter (n = 4; data on the type series of S. doriae from Boulenger 1887b, 1890 and Ouboter 1986) by having generally fewer paravertebral scale rows (62–66 vs. 66–76), fewer ventral scale rows (60–67 vs. 70–79), a greater number of subdigital lamellae on toe IV (18–20 vs. 16–18), higher number of scales around midbody (32 (rarely 30) vs. 26–28), and by the absence of enlarged nuchal scales (vs. present).

Scincella balluca sp. nov. differs from other Indochinese congeners by the following combination of characteristics: from S. alia by having more midbody scale rows (30–32 vs. 26–28), fewer ventral scale rows (60–67 vs. 66–76), more dorsal scale rows between the dorsolateral stripes (6 vs. 4), more subdigital lamellae on toe IV (10–12 vs. 7–10) and toe IV (18–20 vs. 11–13), fewer number of presuboculars (2 vs. 3), and by absent of nuchals (vs. present); from S. apraefrontalis by bigger size (SVL 46.1–57.9 mm vs. 36.1 mm), by having more midbody scale rows (30–32 vs. 18), more paravertebral scale rows (62–66 vs. 52), more ventral scale rows (60–67 vs. 50), more dorsal scale rows between the dorsolateral stripes (6 vs. 4), more infralabials (6 vs. 5), more subdigital lamellae on toe IV (18–20 vs. 8–9), by absent of nuchals (vs. present) and by the presence of prefrontals (vs. absent); from S. auranticaudata by smaller head (SEL 4.8–11 mm vs. 11.1–13.2 mm), by having fewer midbody scale rows (30–32 vs. 34–36), paravertebral scale rows (62–66 vs. 67–74), by absent of nuchals (vs. present) and by the hemipenis with asymmetrical lobes (vs. the hemipenis with symmetrical lobes); from S. badenensis by having fewer midbody scale rows (30–32 vs. 32–36), paravertebral scale rows (62–66 vs. 67–71), ventral scale rows (60–67 vs. 68–74), by absent of nuchals (vs. present), and by non-overlapping limbs (vs. limbs overlapped); from S. darevskii by smaller body size (SVL 46.1–57.9 mm vs. 88.6 mm), by having more midbody scale rows (30–32 vs. 28), fewer supraoculars (4 vs. 5), infralabials (6 vs. 7), and by absent of nuchals (vs. present); from S. devorator by relatively shorter forelimbs (FLL/SVL 0.22–0.27 vs. 0.32–0.33) and hindlimbs (HLL/SVL 0.33–0.37 vs. 0.40–0.42), by having fewer midbody scale rows (30–32 vs. 28–30), by absent of nuchals (vs. present) and by different dorsal coloration pattern (irregularly shaped dark spots vs. two silver grey stripes with irregular spots forming middorsal stripes); from S. fansipanensis by having greater number of superciliaries (7–8 vs. 5–6), postsuboculars (3–5 vs. 2), midbody scale rows (30–32 vs. 22–24), ventral scale rows (60–67 vs. 58–64), dorsal scale rows between the dorsolateral stripes (6 vs. 4), subdigital lamellae on toe IV (10–12 vs. 7–9) and toe IV (18–20 vs. 10–12), and by absent of nuchals (vs. present); from S. honbaensis by having greater number of midbody scale rows (30–32 vs. 28), fewer ventral scale rows (60–67 vs. 73), subdigital lamellae on toe IV (10–12 vs. 15–16) and toe IV (18–20 vs. 21), and by absent of nuchals (vs. present); from S. monticola by having larger number of midbody scale rows (30–32 vs. 23–25), subdigital lamellae on toe IV (10–12 vs. 8–10) and toe IV (18–20 vs. 10–12), dorsal scale rows between the dorsolateral stripes (6 vs. 4), postoculars (2 vs. 1), fewer paravertebral scale rows (62–66 vs. 65–74), and by absent of nuchals (vs. present); from S. melanosticta by having fewer number of midbody scale rows (30–32 vs. 34–37) and dorsal scale rows between the dorsolateral stripes (6 vs. 8); from S. monticola by having larger number of midbody scale rows (30–32 vs. 23–25), subdigital lamellae on toe IV (10–12 vs. 8–10) and toe IV (18–20 vs. 10–12), dorsal scale rows between the dorsolateral stripes (6 vs. 4), postoculars (2 vs. 1), fewer paravertebral scale rows (62–66 vs. 65–74), and by absent of nuchals (vs. present); from S. nigrofasciata by having fewer number of paravertebral scale rows (62–66 vs. 69–74), primary temporals (1 vs. 2), by absent of nuchals (vs. present) and by different dorsal coloration pattern (irregularly shaped dark spots vs. 5–7 dark vertebral stripes); from S. ouboteri by fewer number of enlarged precloacals (2 vs. 4), postoculars (1 vs. 2), primary temporals (1 vs. 2), greater number of postsuboculars (3–5 vs. 2), by absent of nuchals (vs. present), and by different dorsal coloration pattern (irregularly shaped dark spots vs. black vertebral stripe); from S. ochracea by having fewer primary temporals number (1 vs. 2), by absent of nuchals and projecting ear lobules (vs. present) and by different dorsal coloration pattern (irregularly shaped dark spots vs. dark vertebral stripe); from S. reevesii by having fewer primary temporals number (1 vs. 4), fewer dorsal scale rows between the dorsolateral stripes (6 vs. 8), and by absent of nuchals (vs. present); from S. rara by having subdigital lamellae in one row (vs. two rows of subdigital lamellae), greater number of midbody scale rows (30–32 vs. 24), paravertebral scale rows (60–67 vs. 53), subdigital lamellae on toe IV (18–20 vs. 11), and by absent of nuchals (vs. present); from S. rufocaudata by having fewer number of paravertebral scale rows (60–67 vs. 67–69), dorsal scale rows between the dorsolateral stripes (6 vs. 10), primary temporals (1 vs. 2), and by different dorsal coloration pattern (irregularly shaped dark spots vs. 1–3 dark vertebral stripes); from S. rupicola by having fewer midbody scale rows (30–32 vs. 33–36), paravertebral scale rows (62–66 vs. 68–73), ventral scale rows (60–67 vs. 63–69), dorsal scale rows between the dorsolateral stripes (6 vs. 8), and by absent of nuchals (vs. present); and from S. truongi by having greater number of midbody scale rows (30–32 vs. 28), subdigital lamellae on toe IV (18–20 vs. 13–15), preoculars (2 vs. 1) postsuboculars (3–5 vs. 2), fewer number of postoculars (1 vs. 2), primary temporals (1 vs. 2), and by absent of nuchals and projecting ear lobules (vs. present).

The new species Scincella balluca sp. nov. appears to possess a unique hemipenial morphology—deeply bifurcated hemipenes with asymmetrical lobes ( Fig. 4F,G )—distinguishing it from all other known Vietnamese Scincella species for which hemipenial descriptions are available: from S. baraensis with unforked hemipenes with a single lobe, and from S. alia , S. badenensis , S. melanosticta , S. nigrofasciata , S. reevesii , and S. rupicola with deeply bifurcated hemipenes with two symmetrical lobes.

From other Asian congeners, Scincella balluca sp. nov. further differs by the following combination of characteristics: from S. barbouri (Stejneger) , by fewer midbody scale rows (30–32 vs. 24–26), paravertebral scale rows (62–66 vs. 68–79), ventral scale rows (60–67 vs. 70–80), greater number of subdigital lamellae on toe IV (18–20 vs. 14–17), and by its dorsal color pattern (irregularly shaped black spots vs. five indistinct lines); from S. boettgeri by more subdigital lamellae on toe IV (18–20 vs. 15–16); from S. chengduensis (Jia, Ren, Jiang, & Li) by fewer primary temporals (1 vs. 2), midbody scale rows (30–32 vs. 23), more subdigital lamellae on finger IV (10–12 vs. 8–9), and on toe IV (18–20 vs. 10–12), and by its dorsal color pattern (irregularly shaped black spots vs. two longitudinal stripes formed by contiguous, irregularly shaped black maculation); from S. dunan (Koizumi, Ota & Hikida) by more subdigital lamellae on toe IV (18–20 vs. 13–17), and by its dorsal color pattern (irregularly shaped black spots vs. dorsolateral stripes broken by light spots); from S. formosensis by greater number of midbody scale rows (30–32 vs. 26–30), paravertebral scale rows (62–66 vs. 53–65), fewer subdigital lamellae on toe IV (18–20 vs. 14–17), and by non-overlapping limbs (vs. limbs overlapped); from S. huanrenensis (Zhao & Huang) by a greater TD/PDD ratio (1.66–3.33 vs. 0.61–1.14); from S. liangshanensis (Jia, Gao, Wu, Ren, Jiang & Wu) by having a greater number of midbody scale rows (30–32 vs. 23–27) and the number of subdigital lamellae on toe IV (18–20 vs. 10–15), and fewer paravertebral scale rows (62–66 vs. 69–80), the number of primary temporals (1 vs. 2), and the absence of nuchals (vs. present); from S. potanini by a greater TD/PDD ratio (1.66–3.33 vs. 0.79–1.25), more midbody scale rows (30–32 vs. 24–27), subdigital lamellae on toe IV (18–20 vs. 10–12), fewer paravertebral scale rows (62–66 vs. 62–80), and by different dorsal coloration pattern (irregularly shaped dark spots vs. vertebral black stripe); from S. przewalskii (Bedriaga) by having more supraoculars (4 vs. 3) and more subdigital lamellae on toe IV (18–20 vs. 17); from S. punctatolineata (Boulenger) by a larger body size (46.1–57.9 vs. 37.8), and more subdigital lamellae on finger IV (10–12 vs. 9) and on toe IV (18–20 vs. 15); from S. schmidti (Barbour) by the absence of nuchals (vs. present); from S. tsinlingensis (Hu & Zhao) by a greater TD/PDD ratio (1.66–3.33 vs. 0.80– 1.14), greater number of subdigital lamellae on toe IV (18–20 vs. 13–16), and fewer ventral scale rows (60–67 vs. 83–98); from S. victoriana (Shreve) by having smooth scales on dorsum and tail (vs. keeled); from S. vandenburghi (Schmidt) by greater number of midbody scale rows (30–32 vs. 28), fewer paravertebral scale rows (62–66 vs. 69), and fewer subdigital lamellae on toe IV (18–20 vs. 14); and from S. wangyuezhaoi (Jia, Gao, Huang, Ren, Jiang & Li) by having a greater number of midbody scale rows (30–32 vs. 27–30), a greater number of subdigital lamellae on toe IV (18–20 vs. 14–15), fewer primary temporals (1 vs. 2), and the absence of nuchals (vs. present).

Distribution. The new species is currently known from three high-elevation localities in southern Vietnam ( Fig. 1 ): Ta Dung Mt. in Ta Dung NP ( Dak Nong Province), Chu Yang Sin Mt. in Chu Yang Sin NP ( Dak Lak Province), and Bidoup Mt. in Bidoup-Nui Ba NP ( Lam Dong Province). These sites are situated at elevations ranging from approximately 1,600 m (western slope of Chu Yang Sin Mt.) to 2,200 m asl (Bidoup Mt. summit). Given the ecological similarity of the adjacent montane areas, it is likely that the new species’ distribution extends further, potentially encompassing additional highland ridges across the Langbian Plateau at elevations above 1,600 m asl.

Natural history notes. At the type locality on Ta Dung Mt. ( Dak Nong Province), the new species inhabits high-elevation montane cloud elfin forests at elevations between 1,760 and 1,980 m asl. These forests are composed of trees from the families Fagaceae Dumort. , Lauraceae Juss. , and Magnoliaceae Juss. , characterized by a thick leaf litter layer, numerous fallen logs, and small, slow-flowing streams with sandy or clay beds. Notably, the presence of this species indicates a distinct ecological transition from lower-elevation polydominant evergreen tropical forests dominated by Dipterocarpaceae Blume and Fagaceae (including Lithocarpus spp. Blume, Castanopsis spp. (D. Don) Spach, and Quercus sp. L.) to high-elevation evergreen elfin forests dominated by the trees of the families Fagaceae , Lauraceae , and Magnoliaceae . During the survey period at Ta Dung Mt., air temperatures ranged from 20–22°C at daytime, while at night temperatures dropped to 16.5–18°C. Both air and soil humidity levels remained consistently high, reaching up to 98%, primarily during twilight hours between 16:00 h and 20:00 h. Individuals were observed while actively foraging within the leaf litter, among rocks, and around dense root systems. Notably, another skink species, Sphenomorphus cf. yersini Nguyen, Nguyen, Nguyen, Orlov & Murphy inhabits the high-canopy polydominant forests at lower elevations but it was never observed above ca. 1,800 m asl. Similarly, the new species was not recorded at lower elevations, and to date it was not recorded in the same biotope with Sphenomorphus cf. yersini . At the type locality, Scincella balluca sp. nov. was found in sympatry with other reptile species, including Gonyosoma iadinum Poyarkov, Bragin, Idiiatullina, Tran, Le , David & Nguyen ( Colubridae ), Trimeresurus vogeli David, Vidal & Pauwels ( Viperidae ), and Cyrtodactylus ziegleri Nazarov, Orlov, Nguyen & Ho ( Gekkonidae ).

In Chu Yang Sin NP, Dak Lak Province, the new species inhabits montane polydominant evergreen forests that transition into montane thickets and elfin forest formations at the summits of ridges along the southwestern slopes of Chu Yang Sin Mt. at elevations above 1,600 m asl. These forests begin at the upper boundary of pine woodlands and are characterized by the presence of intermittent cascading streams and a well-developed leaf litter layer. The tree canopy is dominated by species from the families Fagaceae ( Lithocarpus , Quercus ), Elaeocarpaceae D.Don ( Elaeocarpus L.), Theaceae Juss. , Lauraceae , Araliaceae Juss. , and Rutaceae Juss. , with the presence of Dacrycarpus imbricatus (Lamb.) De Laub. and Fokienia hodginsii (Dunn) A. Chev. The understory is composed of Lyonia annamensis (Gagnep.) H. S. Lo and dense, low thickets of bamboos from the genus Bambusa Schreb. ( Tordoff et al. 2004; Poyarkov et al. 2014). During the observation period, diurnal temperatures ranged from 21– 24°C, while nocturnal temperatures varied between 17.5 and 21°C. In the afternoon, clouds frequently descend from the summit, occasionally bringing brief but heavy rainfalls that typically cease by twilight. A single specimen was encountered in late April at 18:00, while actively foraging through the litter composed of leaves and conifer needles. At Chu Yang Sin Mt., Scincella balluca sp. nov. was recorded in sympatry with Cyrtodactylus ziegleri ( Gekkonidae ).

In Bidoup-Nui Ba NP, Lam Dong Province, Scincella balluca sp. nov. inhabits the summit, slopes, and surrounding ravines of Mount Bidoup at elevations ranging from 1,900 to 2,200 m asl. This area is characterized by a topography with gentle slopes and is covered by montane cloud elfin forests with the dark-coniferous pine forests at lower elevations. These forests are distinguished by high humidity due to persistent fog, a dense layer of mosses and ferns, a closed canopy, and a well-developed leaf litter layer. The forest is dominated by the tree species belonging to the families Fagaceae ( Lithocarpus spp. , Castanopsis spp. , Quercus spp. ), Eleaocarpaceae ( Elaeocarpus spp. ), Lauraceae ( Neolitsea sp. (Blume) Koidz., Machilus sp. Nees), Magnoliceae ( Magnolia sp. L.), Fabaceae ( Archedendron sp. (Benth.) G. P. Lewis), Melastomataceae Juss. ( Melastoma sp. L.), Illiciaceae R. Br. ( Illicium sp. L.), Aquifoliaceae R. Br. ( Ilex sp. L.), Rutaceae ( Euodia sp. Blume), and Rubiaceae ( Lasianthus sp. Jack, Psychotria sp. L.). Due to the dense leaf litter layer, the herbaceous stratum is poorly developed, consisting mainly of tussock-forming grasses (families Cyperaceae Juss. , Gesneriaceae Lindl. , Violaceae Martinov ) and ferns ( Kuznetsov et al. 2006). Skinks were observed to be active in the leaf litter during daytime and twilight hours from early July to late August. At Bidoup Mt., Scincella balluca sp. nov. was found in sympatry with other reptile species, including Cyrtodactylus bidoupimontis Nazarov, Poyarkov, Orlov, Phung, Nguyen, Hoang & Ziegler ( Gekkonidae ), Calamaria strigiventris Poyarkov, Nguyen, Orlov & Vogel ( Calamariidae ), and Fimbrios klossi Smith ( Xenodermidae ). As observed at the type locality, in both Chu Yang Sin NP and Bidoup-Nui Ba NP, the new species is confined to evergreen or mixed evergreen-coniferous forests at elevations above 1,700 m asl. At lower elevations, below 1,700 m asl, within mixed and coniferous forests, it appears to be ecologically replaced by Sphenomorphus cf. yersini . In both Chu Yang Sin and Bidoup-Nui Ba NPs, the two species were never observed in sympatry, further suggesting altitudinal segregation between them.

Conservation status. The species currently holds no known value for local communities as a source of traditional medicine or food. Field observations indicate that it is relatively abundant within its known range and is frequently encountered, often representing one of the most dominant herpetofaunal species in the surveyed habitats. Nevertheless, Scincella balluca sp. nov. appears to be restricted to undisturbed primary montane habitats on mountain summit ecosystems that, while formally protected within national parks, are among the most susceptible to agricultural encroachment and habitat degradation in Vietnam ( Orlov & Ananjeva 2007; Poyarkov et al. 2021, 2023). The primary threat to the species is likely to be habitat modification through the destruction or alteration of high-elevation evergreen and elfin forest communities. Given the limited knowledge regarding its actual distribution, population trends, and potential threats beyond the currently surveyed sites, S. balluca sp. nov. should be provisionally assessed as Data Deficient (DD) under the IUCN Red List criteria ( IUCN 2025). Further field surveys and ecological studies are essential to delineate its geographic range and evaluate its conservation status more accurately.

Figures

FIGURE 1. Distribution of the genus Scincella in Vietnam. Figures with a dot indicate the type localities of the corresponding species. Coordinates and references of the localities are provided in Table 7. Localities: Scincella balluca sp. nov. (yellow): 1—Ta Dung Mt., Ta Dung NP, Dak Nong (type locality, this study), 2—Chu Yang Sin NP, Dak Lak, 3—Bidoup-Nui Ba NP, Lam Dong, 4—Nui Ba Mt. (Langbian Mt.)., Lam Dong; S. alia: 5—Chieu Lau Thi Mt., Ha Giang (type locality), 6—Tay Con Linh Mt., Ha Giang; S. apraefrontalis: 7—Huu Lien NR, Lang Son (type locality), 8—Pu Hoat NR, Nghe An; S. auranticaudata: 9—Ta Kou Mt., Binh Thuan (type locality); S. badenensis: 10—Ba Den Mt., Tay Ninh (type locality); S. baraensis: 11—Ba Ra Mt., Binh Phuoc (type locality), 12—Bu Gia Map NP, Binh Phuoc, 13—Ma Da NR, Dong Nai; S. darevskii: 14—Tuan Giao, Dien Bien (type locality); S. devorator: 15—Yen Tu Mt., Quang Ninh (type locality), 16—Ba Vi NP, Ha Noi; 17—Copia NR, Son La, 18—Xuan Lien NR, Thanh Hoa; S. cf. doriae: 19—Ba Na-Nui Chua NR, Da Nang, 20—Ma Da NR, Dong Nai; S. fansipanensis: 21—Fansipan Mt., Lao Cai (type locality); S. honbaensis: 22—Hon Ba Mt., Hon Ba NR, Khanh Hoa (type locality); S. cf. melanosticta: 23—Phong Nha-Ke Bang NP, Quang Binh, 24—Kon Chu Rang NR, Gia Lai, 25—Hoa Tam, Dong Hoa, Phu Yen, 26—Hoa Thinh, Tay Hoa, Phu Yen, 27—Langbian Pl. (no exact locality), Lam Dong, 28—Con Dao NP, Ba Ria-Vung Tau; S. monticola: 29—Muong Nhe NR, Dien Bien, 30—Phia Oac-Phia Den NP, Cao Bang, 31—Mau Son Mt., Lang Son; S. nigrofasciata: 32—Dak Nong UNESCO Global Geopark, Dak Nong, 33—Nam Nung NR, Dak Nong, 34—Bu Gia Map NP, Binh Phuoc, 35—Bao Loc, Lam Dong, 36—Thi Vai Mt., Ba Ria-Vung Tau, 37—Dinh Mt., Ba Ria-Vung Tau; S. ouboteri: 38—Ngoc Son-Ngo Luong NR, Hoa Binh (type locality); S. ochracea: 39—Muong Nhe NR, Dien Bien, 40—Sop Cop NR, Son La; S. rara: 41—Buon Luoi, Gia Lai (type locality); S. reevesii: 42—Vi Xuyen, Ha Giang, 43—Phia Oac-Phia Den NP, Cao Bang, 44—Bai Tu Long NP, Quang Ninh, 45—Cat Ba NP, Hai Phong, 46—Chi Linh, Hai Duong, 47—Cao Pha, Son La, 48—Nam Dong NR, Thanh Hoa, 49—Ben En NP, Thanh Hoa, 50—Ky Anh, Ha Tinh; S. rufocaudata: 51—Buon Luoi, Gia Lai (type locality), 52—Tam Dao NP, Vinh Phuc, 53—Phong Nha-Ke Bang NP, Quang Binh, 54—Sao La NR, Thua Thien-Hue, 55—Nam Giang, Phuoc Son, Quang Nam, 56—Kon Plong, Kon Tum, 57—Chu Mom Ray NR, Kon Tum, 58—Kon Ka Kinh NP, Gia Lai; 59—K’Bang, Gia Lai, 60—Ea Kao, Dak Lak, 61—Con Dao NP, Ba Ria-Vung Tau; S. rupicola: 62—Ta Cu Mt., Binh Thuan; S. truoingi: 63—Sop Cop NR, Son La (type locality).

FIGURE 3. Holotype of Scincella balluca sp. nov. (ZMMU Re-18292, male) in life. Photograph by A.M. Bragin.

FIGURE 4. Holotype of Scincella balluca sp. nov. (ZMMU Re-18292, adult male) in preservative. A. Ventral view of head; B. Dorsal view of head; C. Right lateral view of head; D. Ventral view of left forelimb; E. Ventral view of left hindlimb; F. Ventral view of right hemipenis, partially everted, the black line indicates the sulcus spermaticus; G. Dorsal view of right hemipenis, partially everted, not to scale; H. Dorsal view of body; I. Ventral view of body. Scale bars: A–C = 3 mm; D, E = 3 mm; F, G = 1.5 mm; H, I = 20 mm. Photographs by A.M. Bragin.

FIGURE 5. Head scale nomenclature and their positional relationship and size illustrated for the adult male Scincella balluca sp. nov. (holotype, ZMMU Re-18292). A. Left lateral view; B. Dorsal view; C. Ventral view. Terminology is modified from Ouboter (1986), Grismer et al. (2019), and Bragin et al. (2025). AL—anterior loreal, C—ciliary, Cs—chinshield; F—frontal, FN—frontonasal, FP—frontoparietal, IF—infralabial, IP—interparietal, LST—lower secondary temporal, LPT—lower pretemporal, LPSL—lower postsupralabial, M—mental, N—nasal, P—parietal, PF—prefrontal, PL—posterior loreal, PM— postmental, PR—preocular, PRS—presubocular, PT—primary temporal, PSO—postsubocular, PO—postocular, R—rostral, SC—superciliaries, SL—supralabial, SO—supraocular, TT—tertiary temporal, UPT—upper pretemporal, UPSL—lower postsupralabial, UST—upper secondary temporal, and *—small scales separating supralabials from the lower eyelid. Illustration by A.M. Bragin.

FIGURE 6. The type specimens of Scincella balluca sp. nov. in life A. Ventral view of male (paratype, VRTC NAP15390); B. Lateral body view of male (holotype, ZMMU Re-18292); C. Lateral body view of female (paratype, ZMMU Re-18295); D. Lateral body view of juvenile (VRTC NAP15324). Scale bars: A = 10 mm; B–D = 20 mm. Photographs by A.M. Bragin.