Adult male ZMKU R 00959 from Tham Than Lot Noi-Tham Than Lot Yai Nature Trail, Chaloem Rattanakosin National Park, Khao Chot Subdistrict, Si Sawat District, Kanchanaburi Province, Thailand (14.66930°N, 99.29060°E, 526 m a.s.l.), collected by Korkhwan Termprayoon, Akrachai Aksornneam, Natee Ampai, and Siriporn Yodthong on 20 April 2019.

Adult males ZMKU R 00958 and ZMKU R 00960 and adult females ZMKU R 00961–64 bear the same collection site as the holotype.

Cyrtodactylusfluvicavus sp. nov. can be separated from all other species of the brevipalmatus group by the combination of having 11–13 supralabials, 9 or 10 infralabials, 26–30 paravertebral tubercles, 14–18 rows of longitudinally arranged tubercles, 30–39 transverse rows of ventrals, 154–175 longitudinal rows of ventrals, 9–11 expanded subdigital lamellae on the fourth toe, 10–13 unexpanded subdigital lamellae on the fourth toe, 19–22 total subdigital lamellae on the fourth toe; 7–9 expanded subdigital lamellae on the fourth finger, 9–11 unexpanded subdigital lamellae on the fourth finger, 17–19 total subdigital lamellae on the fourth finger; 9–12 total enlarged femoral scales, 8–11 total femoral pores in males; 14 or 15 precloacal pores in males; 14 or 15 enlarged precloacals; enlarged femorals and enlarged precloacals not continuous; proximal femorals less than one-half the size of the distal femorals; small tubercles on forelimbs and flanks; small dorsolateral caudal tubercles and narrow ventrolateral caudal fringe; ventrolateral caudal fringe composed scales of different size; tail circular in cross-section; slightly enlarged unpaired medial subcaudals not posteromedially furrowed; maximum SVL 78.2 mm; three dark transverse body bands (Tables 4–6).

(Fig. 4). Adult male SVL 72.5 mm; head moderate in length (HL/SVL 0.28), width (HW/HL 0.70), depth (HD/HL 0.42), distinct from neck, triangular in dorsal profile; lores concave slightly anteriorly, weakly inflated posteriorly; prefrontal region concave; canthus rostralis rounded; snout elongate (ES/HL 0.42), rounded in dorsal profile; eye large (ED/HL 0.25); ear opening obliquely elongate, small; eye to ear distance greater than diameter of eye; rostral rectangular, divided by a deep furrow, bordered posteriorly by large left and right supranasals and one small azygous internasal, bordered laterally by first supralabials; external nares bordered anteriorly by rostral, dorsally by large supranasal, posteriorly by two smaller postnasals, bordered ventrally by first supralabial; 12R/12L rectangular supralabials, second through seventh supralabials nearly same size as first, then tapering abruptly below eye; 10R/10L infralabials tapering smoothly to just below and slightly past posterior margin of eye; scales of rostrum and lores flat to domed, larger than granular scales on top of head and occiput; scales of occiput intermixed with distinct, small tubercles; superciliaries subrectangular, largest dorsally; mental triangular, bordered laterally by first infralabials and posteriorly by large left and right trapezoidal postmentals contacting medially for 50% of their length posterior to mental; one row of slightly enlarged, elongate sublabials extending posteriorly to sixth(L) and fifth(R) infralabial; gular and throat scales small, granular, grading posteriorly into slightly larger, flatter, smooth, imbricate, pectoral and ventral scales.

Body relatively short (AG/SVL 0.46) with well-defined ventrolateral folds; dorsal scales small, granular interspersed with larger, conical, semi-regularly arranged, weakly keeled tubercles; tubercles extend from occipital region onto base of tail and slightly beyond as paravertebral rows; smaller tubercles extend anteriorly onto nape and occiput, diminishing in size anteriorly; approximately 17 longitudinal rows of tubercles at midbody; approximately 30 paravertebral tubercles; small tubercles on flanks; 34 longitudinal rows of flat, imbricate, ventral scales much larger than dorsal scales; 155 transverse rows of ventral scales; 15 large, pore-bearing, precloacal scales; no deep precloacal groove or depression; and two rows of post-precloacal scales on midline.

Forelimbs moderate in stature, relatively short (ForL/SVL 0.14); granular scales of forearm slightly larger than those on body, interspersed with large tubercles; palmar scales rounded, slightly raised; digits well-developed, relatively short, inflected at basal interphalangeal joints; digits narrower distal to inflections; subdigital lamellae wide, transversely expanded proximal to joint inflections, narrower transverse lamellae distal to joint inflections; claws well-developed, claw base sheathed by a dorsal and ventral scale; 8R/8L expanded and 10R/10L unexpanded lamellae beneath the fourth finger; hind limbs larger and thicker than forelimbs, moderate in length (TibL/SVL 0.16), covered dorsally by granular scales interspersed with moderately sized, conical tubercles dorsally and posteriorly and anteriorly by flat, slightly larger, subimbricate scales; ventral scales of thigh flat, subimbricate, larger than dorsals; subtibial scales flat, imbricate; one row of 5R/6L enlarged pore-bearing femoral scales not continuous with enlarged pore-bearing precloacal scales, terminating distally at knee; proximal femoral scales smaller than distal femorals, the former forming an abrupt union with much smaller, rounded, ventral scales of posteroventral margin of thigh; plantar scales flat; digits relatively long, well-developed, inflected at basal interphalangeal joints; 9R/9L wide, transversely expanded subdigital lamellae on fourth toe proximal to joint inflection extending onto sole, and 11R/11L unexpanded lamellae beneath the fourth toe; and claws well-developed, claw base sheathed by a dorsal and ventral scale.

Tail original, 97.6 mm long (TL/SVL 1.34), 5.2 mm in width at base, tapering to a point; sub-circular or nearly round in cross-section; dorsal scales flat, square bearing tubercles forming paravertebral rows and small tubercles forming a dorsolateral longitudinal row; slightly larger, posteriorly directed, semi-spinose tubercles forming narrow but distinct ventrolateral caudal fringe; larger scales of ventrolateral fringe occur at regular intervals; medial subcaudals slightly enlarged but not paired, distinctly enlarged single medial subcaudals absent; subcaudals, larger than dorsal caudals; base of tail bearing hemipenial swellings; 3R/2L conical postcloacal tubercles at base of hemipenial swellings; and postcloacal scales flat, imbricate.

(Fig. 5). Ground color of the head, body, limbs, and tail brown; faint, diffuse mottling on the top of the head; thin, dark brown postorbital stripe; ventral portion of lores and suborbital region dark brown; nuchal band faint, bearing two dark-colored posterior projections; paired dark brown paravertebral blotches on nape; three wide faint irregularly shaped body bands edged in dark brown between limb insertions; band interspaces bearing irregularly shaped dark-colored markings; dark-colored speckling on limbs and digits; digits bearing pale-colored bands; eight wide dark-colored caudal bands separated by seven pale-colored bands; first six dark-colored and seven pale-colored caudal bands encircle tail; all ventral surfaces beige, generally immaculate; iris orange-gold in color.

(Fig. 5). Individuals of the type series are very similar in overall coloration and pattern. TL and TW of complete original tails (ZMKU R 00959–00960, ZMKU R 00963–00964) are 79.7–97.6 mm (mean 91.4 ± 8.2 mm; N = 4) and 4.0–5.2 mm (mean 4.5 ± 0.5; N = 4), respectively. The posterior one-third of the tail of ZMKU R 00958 is regenerated (TL 72.0 mm, TW 4.9 mm); that of ZMKU R 00962 is missing (TL 83.8 mm, TW 4.4 mm); and that of ZMKU R 00961 is broken one-third of the way passed the base and nearly all of the broken section is regenerated (TL 73.6 mm, TW 4.07 mm). Regenerated tail sections lack a color pattern. ZMKU R 00963–64 have seven dark-colored and six pale-colored caudal bands as opposed to eight and seven bands, respectively, in the holotype. ZMKU R 00958, ZMKU R 00960, ZMKU R 00962, ZMKU R 00964 are slight less boldly marked than the holotype. Meristic and morphometric differences are listed in Table 5.

Cyrtodactylusfluvicavus sp. nov. is currently known from the type locality at Tham Than Lot Noi-Tham Than Lot Yai Nature Trail in Chaloem Rattanakosin National Park, Si Sawat District, Kanchanaburi Province, western Thailand (Fig. 1).

The specific epithet fluvicavus comes from the Latin fluvius, meaning stream, river, or flow and the Latin cavus, meaning hollow or hole and refers to a landmark cave in the Chaloem Rattanakosin National Park which has a stream that flows through it.

Cyrtodactylusfluvicavus sp. nov. is the sister species to a clade composed of ten lineages in a phylogenetic sequence of C. sp.9, C. sp.10, Cyrtodactylusuthaiensis sp. nov., C. sp.11, C.interdigitalis, C.cf.ngati1, C.cf.ngati2, C.ngati3, and the sister lineages C.ngati4 and C.ngati (Fig. 2). Cyrtodactylusfluvicavus sp. nov. differs from those lineages by an uncorrected pairwise sequence divergence of 9.55–12.13% and from all members of the brevipalmatus group by 11.61–20.26% (Table 2). It differs categorically from C.elok by having as opposed to lacking paravertebral tubercles and femoral pores, and by having 14–18 as opposed to 4–7 longitudinal rows of tubercles. It differs from C.brevipalmatus, C.interdigitalis, C.ngati, C.ngati3, C.rukhadeva, and C. sp.9 in having statistically significant different mean values of the morphometric characters of AG, HumL, ForL, FemL, TibL, HL, HW, HD, EE, ES, EN, EL and IN (Table 6). It differs further from C.brevipalmatus, C.interdigitalis, C.ngati, C.ngati3, C.rukhadeva, and C. sp.9 in having statistically significant different mean values of the meristic characters of SL, PVT, LRT, VS, VSM, TL4E, TL4T, FL4E, FL4U, FL4T, FS, PCS, and BB. Statistically significant and discrete differences between Cyrtodactylusfluvicavus sp. nov. and all other species and populations are presented in Tables 4–6.

All individuals were found in karst forests bearing mixed deciduous and dry evergreen trees amidst rocky streams and a nearby waterfall (Fig. 6). This area is surrounded by agricultural fields and residential areas. Specimens (N = 7) were collected at night (1900–2100 h) during the dry season (April) on the tree trunks or palm tree leaves (57.1%; N = 4), twigs of shrubs (14.3%; N = 1), karst walls (14.3%; N = 1), and a wooden bridge (14.3%; N = 1) at 526 m elevation with a temperature of 31.9 °C and relative humidity of 56.9%. The holotype (ZMKU R 00959) and two specimens (ZMKU R 00960, ZMKU R 00962) were found on tree trunks ≤ 100 cm above ground level. One specimen (ZMKU R 00964) was found on a palm tree branch approximately 50 cm above the ground. Another specimen (ZMKU R 00963) was found on the twig of a shrub. Another specimen (ZMKU R 00961) was found on a karst wall approximately 3 m above the ground, and another (ZMKU R 00958) on a wooden bridge over a stream. Given these observations, this species appears to be an arboreal habitat generalist. The new species was found to co-occur with two other species of gekkonid lizards, Cyrtodactylusmonilatus Yodthong, Rujirawan, Stuart, Grismer, Aksornneam, Termprayoon, Ampai & Aowphol, 2022 and Dixoniussiamensis (Boulenger, 1899).