Sphenomorphus striatafaucium, Quah & Grismer, 2025

Sphenomorphus striatafaucium sp. nov.

Bornean Stripe-throated Skink

http://zoobank.org/ urn:lsid:zoobank.org:act:18BD42EB-B34B-488B-BDFA-2BF2455DC1DA

( Figs. 2 View FIGURE 2 & 3 View FIGURE 3 )

Sphenomorphus stellatus View in CoL : Bacon 1967: 67–71; Inger et al. 2001: 183; Malkmus et al. 2002: 283; Das 2004: 7, 2006: 13, 2010: 250; Grismer 2011: 670 (in part); Karin et al. 2016: 408; Bauer & Das 2024: 40.

Holotype. Adult male FMNH 138554 from near Nanga Tekalit on the Mengiong River , Kapit District, Third Division, Sarawak, Malaysia (estimated GPS coordinates N 1.90196, E 112.57299, 29 m in elevation) collected by Mr. F.W. King on 14 December 1962. GoogleMaps

Diagnosis. Sphenomorphus striatafaucium sp. nov. can be separated from all other species of Sphenomorphus by having the unique combination of a SVL of 57.4 mm; head, body, and supracaudal scales smooth; frontal scale undivided; prefrontals in broad contact; parietals in contact posterior to interparietal; parietals not divided; six scales bordering the parietals; four nuchals; four supraoculars; two loreals; anterior loreal not divided; loreals in contact with supralabials; postnasal groove absent; eight superciliaries; superciliary row not interrupted by fourth supraocular; lower eyelid scales large, no enlarged, clear, central disc; seven or eight supralabials; six infralabials; three pairs of chinshields; one primary temporal scale; two secondary temporals; upper secondary temporal large; no subtemporals; 24 midbody scale rows; 62 paravertebrals; paravertebrals not wider than other dorsals; 66 ventrals; two enlarged precloacals; 15 scales around tail at level of tenth subcaudal; first five rows of anterior subcaudals divided; subcaudals enlarged; 19 subdigital lamellae on fourth toe; 12 subdigital lamellae on fourth finger; no wide, dark, vertebral or lateral stripes or blotches; top of head unpatterned; absence of dark transverse subcaudal bars on original portion of tail; absence of thin, dark, dorsal caudal bands; distinct vertical rows of three or four white spots with dark dorsal and ventrolateral borders along original tail; labial margins edged with black; distinct series of dark obliquely oriented longitudinal stripes on the chin and throat which fade in the pectoral region. Note that these characters are based on a single specimen, which may render some of these characters not truly diagnostic and other characters not listed here as diagnostic with the acquisition of additional material in the future ( Table 1 View TABLE 1 ).

Description of holotype ( Table 1 View TABLE 1 ). Adult male, SVL 57.4 mm ( Fig. 2 View FIGURE 2 & 3 View FIGURE 3 ); tail broken, remaining portion 19.0 mm; head moderately sized, subtriangular, distinct from neck; snout slightly pointed, semicircular in dorsal and lateral profile; head scales large, smooth ( Fig. 3A–C View FIGURE 3 ); HL 8.9 mm; HW 7.2 mm; head somewhat depressed, HH 5.4 mm; rostral wider than tall, in contact with first supralabials and nasals laterally, frontonasal dorsally; frontonasal undivided, wider than long, in contact with nasal and anterior loreal laterally, prefrontals posteriorly; prefrontals in medial contact, contacting loreals and first superciliaries and frontal posteriorly; frontal subtriangular, in point contact with first superciliaries but contacting first and second supraoculars laterally and frontoparietals posteriorly; four supraoculars, first subtriangular, second rectangular, third rectangular, fourth hemispherical; frontoparietals paired, in medial contact, each in contact with second, third and fourth supraoculars laterally and parietals and interparietal posteriorly; interparietal somewhat diamond-shaped, eyespot present posteriorly; parietals in medial contact posterior to interparietal, contacting upper supratemporal laterally and nuchals posteriorly; six scales bordering posterolateral margins of parietals, four of them nuchals; seven (R), eight (L) supralabials, 4 th and 5 th largest and below eye, 2 nd and 3 rd not keeled; nostril in lower part of nasals; nasals large, in contact with first supralabials ventrally, anterior loreal posteriorly; no deep postnasal groove; two rectangular, undivided loreals similar in size contacting supralabials; posterior loreal in contact with second and third supralabials ventrally on left, second supralabial on right, preoculars posteriorly, first superciliary and frontonasal dorsally; two preoculars, lower much larger than upper; eight (R,L) superciliaries not interrupted by fourth supraocular; two presuboculars; lower eyelid bearing large scales and lacking enlarged, clear, central disc; post-temporal in ventral contact with primary temporal and posterior contact with parietal; upper secondary temporal contacts parietal; subtemporals absent; three postsuboculars, first two contacting fifth and sixth supralabials; one postsupraocular; one primary temporal, two secondary temporals; two tertiary temporals; two postsupralabials; six (R,L), infralabials, first two contacting postmental, first smaller than second, not elongate; mental large, hemispherical; postmental large, single; three pairs of large chinshields, first two pairs in broad contact with supralabials; second pair separated by a gular scale, third pair separated by three gulars; external ear opening large, vertically ovoid, vertical diameter of TD 1.2 mm, horizontal diameter 1.1 mm, lacking anterior lobules; tympanum deeply recessed.

Body scales smooth, cycloid, imbricate; dorsals larger than ventrals and flank scales; 62 paravertebral scale rows not intermittently interrupted by smaller scales, not wider than adjacent dorsals; 24 longitudinal scale rows around midbody; 66 ventrals; two damaged enlarged, medial, precloacals not overlapping lateral precloacals; supracaudals smooth, 15 scale rows at 10 th subcaudal; subcaudals larger than dorsal caudals ( Fig. 3D View FIGURE 3 ), somewhat transversely elongate, larger than lateral caudals, first five anterior rows divided; limbs moderately robust, in contact when adpressed; palmar and plantar scales low, rounded; single row of supradigitals; 12 (R,L) smooth, subdigital lamellae on fourth finger; 19 (R, L) weakly keeled, subdigital lamellae on fourth toe. Other measurements recorded (all in mm): AG = 30.8, SNL = 4.1, SFL = 19.8, STL = 10.0, ED = 2.8, ET = 4.1, FIL ± 10.4, HIL ± 13.5.

Colouration in preservation ( Fig. 2 View FIGURE 2 & 3 View FIGURE 3 ). The colouration of the specimen has remained largely the same as when it was first reported by Bacon (1967), except for some fading after 62 years of storage. The dorsum, flanks, dorsal surfaces of head and tail have a nearly immaculate bronze base colouration. It appears there is a very faint, light vertebral stripe that would have been more prominent in-life but has now almost completely faded. The supralabials and infralabials are beige and bordered with darker bronze barring which gives the lips a spotted appearance. The bronze barring also borders the similarly beige-coloured mental, postmental, and chin shields and runs along the sutures of those scales. The barring then extends as a series of distinct obliquely oriented, dark-bronze stripes between the scale rows of the throat which fade in the pectoral region. The pectoral, abdominal and underside of the tail beige with faint stippling that is most prominent on the precloacal region. The dorsal surfaces of the limbs are bronze with white spots, while the ventral colouration is beige, and the base of the feet and underside of the toes are dark-brown. Along the sides of the bronze-coloured tail are distinct vertical rows of three or four white spots with dark dorsal and ventrolateral borders. The underside of the tail is beige with dark speckling that is most prominent along the border of the subcaudals.

Comparison. Given that the intraspecific ranges and means of meristic characters will vary with the acquisition of additional material we present these as tentative diagnostic characters. We place more weight on the categorical characters given that they do not vary intraspecifically. Sphenomorphus striatafaucium sp. nov. can be distinguished from other members of the S. stellatus group by its unique colour pattern of possessing bold, dark oblique stripes along its chin and throat, and the absence of any dark markings on top of the head ( Table 2 View TABLE 2 ). It can be further differentiated from S. stellatus by the presence of labial sutures edged in black (vs. absent in S. stellatus ) and fewer lamellae on fourth toe (19 vs. 20–26). From S. praesignis , it can be differentiated by its lower number of midbody scale rows (24 vs. 26–29), absence of dark transverse subcaudal bars, thin dark dorsal caudal bands, and large dark anterolateral trunk spots (vs. presence of all three characters in S. praesignis ). Sphenomorphus striatafaucium sp. nov. can be further distinguished from S. phuquocensis by the absence of a postnasal groove (vs. present in S. phuquocensis ) and higher number of paravertebral scales (62 vs. 56). The new species can be further distinguished from S. preylangensis by its potentially fewer number of infralabials (6 vs. 7) and absence of dark transverse subcaudal bars and thin dark dorsal caudal bands (vs. presence of both characters in S. preylangensis ) ( Table 2 View TABLE 2 ; Fig. 4 View FIGURE 4 ).

Sphenomorphus striatafaucium sp. nov. can be further differentiated from other members of the genus found in Borneo by a suite of morphological characters in addition to its unique chin and throat colour pattern of bold, dark oblique stripes. The fewer number of supraoculars in S. striatafaucium sp. nov. (4) differentiates it from S. cyanolaemus (6 or 7), S. haasi (6), S. kinabaluensis (5 or 6), S. maculicollus (7), S. multisquamatus (6 or 7), S. murudensis (6), S. sabanus (6 or 7) and S. tanahtinggi (5). The prefrontals in contact in S. striatafaucium sp. nov. also differentiates it from S. crassus , S. maculicollus and S. tenuiculus that all have separated prefrontals. The presence of enlarged precloacal scales in the new species also differentiates it from S. alfredi . The fewer number of midbody scale rows in S. striatafaucium sp. nov. (24) also differentiates it from S. alfredi (26–30), S. crassus (32), S. cyanolaemus (37–42), S. haasi (41 or 42), S. kinabaluensis (32–38), S. maculicollus (35–36), S. multisquamatus (40–49), S. murudensis (30–32), S. sabanus (38–42), S. tanahtinggi (40–42) and S. tenuiculus (26). The fewer number of ventral scale rows in S. striatafaucium sp. nov. (66) further differentiates it from S. crassus (72), S. cyanolaemus (78–94), S. haasi (93–98), S. kinabaluensis (73–91), S. maculicollus (84), S. multisquamatus (83–101), S. sabanus (71–91) and S. tenuiculus (68). Sphenomorphus striatafaucium sp. nov. also has more paravertebral scale rows than S. tenuiculus (62 vs. 57), but fewer than S. maculicollus (62 vs. 79) and S. tanahtinggi (62 vs. 76–79). The fewer number of supraciliaries in S. striatafaucium sp. nov. (8) also differentiates it from S. buettikoferi (9), S. cyanolaemus (12–16), S. haasi (13 or 14), S. multisquamatus (12–16) and S. sabanus (14–17). Sphenomorphus striatafaucium sp. nov. also has more supralabials S. maculicollus (7 vs. 6) but fewer than S. tanahtinggi (7 vs. 8 or 9). The new species also has more infralabials than S. cyanolaemus (7 vs. 6), S. maculicollus (7 vs. 6) and S. multisquamatus (7 vs. 5). Sphenomorphus striatafaucium sp. nov. also has more subdigital lamellae on the fourth toe than S. alfredi (19 vs. 7–12), S. murudensis (19 vs. 16) and S. tanahtinggi (19 vs. 16 or 17), but fewer than S. buettikoferi (19 vs. 21–23), S. shelfordi (19 vs. 28 or 29) and S. tenuiculus (19 vs. 21–24). The texture of the subdigital lamellae that is keeled in S. striatafaucium sp. nov. also differentiates it from S. maculicollus , S. multisquamatus and S. shelfordi that possess smooth subdigital lamellae. Finally, the absence of a dark dorsolateral stripe differentiates the new species from S. alfredi , S. crassus , S. cyanolaemus , S. shelfordi , S. tanahtinggi and S. tenuiculus ( de Rooij 1915; Inger 1958; Inger & Hosmer 1965; Bacon 1967; Inger et al. 2001; Malkmus et al. 2002; Karin et al. 2016).

Etymology. The specific epithet “ striatafaucium ” is derived from the combination of the words “ striatus ” and “ faucium ” which is Latin for stripe and throat, respectively, in reference to the prominent striped markings on the chin and throat of the holotype.

Distribution ( Fig. 5 View FIGURE 5 ). This species is only known from the site of its collection near Nanga Tekalit on the Mengiong River, Kapit District, Third Division, Sarawak, Malaysia (estimated GPS coordinates N 1.90196, E 112.57299, 29 m in elevation) ( Bacon, 1967).

Natural history. Nothing is known about the natural history of this species because no natural history observations were reported associated with its collection ( Bacon, 1967). Based on what is known about the ecology of other members of the S. stellatus group, the new species is most likely diurnal, terrestrial, scansorial or partially arboreal ( Grismer, 2011). Sphenomorphus stellatus , S. annamiticus and S. preylangensis have all been observed on tree trunks and sheltering in tree cavities and exfoliating bark. All three species have also been found under debris in the leaf litter indicating their terrestrial proclivities ( Grismer et al., 2019).

Conservation status. It is presently unknown how widespread the species is in Borneo as nothing is known about this species except for the type locality. As such, we recommend listing the species as Data Deficient (DD) ( IUCN, 2024).