Ptyctolaemus siangensis, Balan & Das & Boruah & Tillack & Lalronunga & Deepak, 2025

Balan, Amirtha, Das, Abhijit, Boruah, Bitupan, Tillack, Frank, Lalronunga, Samuel & Deepak, Veerappan, 2025, Description of two new species of Ptyctolaemus (Squamata: Agamidae) from northeast India, Vertebrate Zoology 75, pp. 487-516 : 487-516

Ptyctolaemus siangensis sp. nov.

Figures 12 , 13 ; Tables 3 , 4

Chresonymy. Ptyctolaemus aff. gularis – Liu et al. (2021)

Holotype.

WII -ADR 1176 , adult female, from Rottung ( 28.14114°N, 95.1562°E, elevation 390 m a. s. l.), East Siang district, Arunachal Pradesh, India, collected on 22 October 2021 by Bitupan Boruah.

Paratype.

WII -ADR 1210 , adult male, from Pittung ( 28.67146°N, 94.96159°E, elevation 415 m a. s. l.), Upper Siang district, Arunachal Pradesh, India, on 28 October 2021 by Bitupan Boruah ; ZSI -R-29479 , adult male, from Jengging ( 28.53543°N, 95.03106°E, elevation 945 m a. s. l.), Upper Siang district, Arunachal Pradesh, India, on 5 October 2018 by Abhijit Das ; Figure S 2.

Referred specimens.

WII -ADR 2542 , adult female, from Khellong ( 27.0035°N, 92.24502°E, elevation 2955 m a. s. l.), Eaglenest Wildlife Sanctuary, West Kameng district, Arunachal Pradesh, India, on 29 August 2022 by Krishnendu Banerjee ; WII -ADR 465 , adult female, from Potin ( 27.34786°N, 93.8497°E, 580 m a. s. l.), Lower Subansiri district, Arunachal Pradesh, India, on 19 October 2019 by Abhijit Das and Bitupan Boruah .

Description of the holotype.

An adult female, SVL 63.65 mm and TAL 153.95 mm; TAL / SVL ratio 2.42; head distinct from neck, longer than wide ( HW / HL = 0.48), slightly concave on top; rostral scale crescent; snout rounded, longer than orbital diameter ( OD / EN = 0.65); pupil round, scales on the loreal region slightly keeled, surrounded by scales of irregular size and shape; nasal separated from rostral by one scale; canthus rostralis sharp, strongly keeled and consists 13 enlarged scales on each side; keels weak towards the snout; nostrils rounded, slightly laterally positioned, in contact with first supralabials; snout scales irregular in shape and size, series of six enlarged, keeled scales on the snout form an inverted “ Y ” - shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scale on either side is oriented diagonally towards the superciliary ridge; head height at occipital region 9.89 mm; scales on head, snout and interorbital region heterogenous in shape and size; tympanum hidden and covered with smooth scales; neck region with small overlapping scales interspersed with enlarged scales that increase in size towards trunk; three enlarged, keeled, and elevated scales located posterior and horizontal to orbit; scales around orbital region small and irregular in shape; parietal eye is not distinct; gular in males distinct; scales on gular heterogeneous in size and mucronate, feebly keeled, scales in middle region larger than those on anterior and posterior region; three distinct raised gular folds on either side of midline; folds curved towards midline posteriorly (Fig. 7 ); nine supralabials on both sides; seven infralabials on left and eight on right; nuchal crest poorly developed, consisting of 14 conical scales (Tables S 4, S 5).

Mental scale triangular, broader than long, and slightly narrower than the rostral, bordered posteriorly by one infralabial on each side and two enlarged postmentals in contact with the first infralabials; postmentals followed by two small gular scale; four chin shields present on each side, positioned parallel to the infralabials; the anterior portion of the first chin shield contacts the first infralabial, while the remaining part of the first and the subsequent two chin shields separated from the infralabials by one intervening scale row; scales in the anterior gular region feebly keeled.

Habitus slender, slightly compressed, dorsal scales keeled, imbricate, and posteriorly pointed; mid-dorsal scale row strongly keeled, enlarged scales appearing discontinuously; lateral scales heterogeneous, mostly smaller than the dorsal, feebly keeled, imbricate, and interspersed with enlarged, strongly keeled scales; 89 dorsal scales ( VTSR); 87 scales around midbody; 132 ventral scales, larger than lateral scales and approximately equal to the enlarged dorsal scales, strongly keeled, imbricate, posteriorly pointed.

Limbs are slender, moderate sized, dorsal surface covered in strongly keeled, imbricate scales; lower arm length slightly longer than the upper arm length ( UAL / LAL = 0.94); femur length slightly longer than the crus length (femur / crus = 1.03); scales on dorsal surface of the forelimbs strongly keeled, uniform and imbricate; scales on ventral side of the forelimbs relatively smaller, feebly keeled; relative length of digits: IV > III > II > V > I; scales on dorsal side of the hindlimb slightly enlarged, keeled and imbricate; scales on ventral side of the hindlimb smaller than the dorsal, slightly keeled and imbricate; relative length of toes: IV > III > V > II > I; 30 / 30 subdigital lamellae under fourth toe and bicarinate.

Tail length more than twice of SVL, rounded, slightly compressed laterally, broader at the base, gradually tapering towards tip, covered with regularly arranged strongly keeled, imbricate and homogeneous scales.

Diagnosis.

A moderate-sized lizard, SVL 66.90–77.68 mm in male (n = 2) and SVL 58.03–66.62 mm in female (n = 3), TAL 157.56–189.96 mm in male (n = 2) and 140.75–153.95 mm in female (n = 3). Snout scales irregular in shape and size with an inverted Y-shaped pattern. Nuchal crest poorly developed with 14–24 conical scales. Body slightly compressed, scales at the trunk heterogeneous in size, smaller than the dorsal, slightly keeled, oriented backwards, 89–114 dorsal scales ( VTSR), 86–105 rows of scales around midbody and 132–148 ventrals. Mental broader than long, postmentals medially separated by a single small gular scale, anterior region of the first chin shield contacts the first infralabial, gular with three distinct raised gular folds on either side of midline excluding the base, gular scales heterogeneous in size, feebly keeled, scales in middle region larger than those on anterior and posterior region.

Comparison.

Ptyctolaemus siangensis sp. nov. can be distinguished from Ptyctolaemus collicristatus by having relatively smaller SVL / TAL ratio 0.41–0.45 (vs. 0.47–0.56; Table 3 ), gular region with dark blue with white lines vs bright yellow medially with greenish-yellow and dark brown laterally; differs from Ptyctolaemus gularis by gular region with dark blue with white lines (vs. pale-brown or pale-bluish green or pale-yellowish green; three to four broad dark-blue stripes; Fig. 13 ); differs from Ptyctolaemus chindwinensis by relatively fewer scales on the nuchal crest 18–24 (vs. 26–29), gular region with dark blue with white lines vs bright yellow with two horizontal parallel black stripes (Fig. 13 ).

Morphological variation.

Details of morphometric and meristic variation among the type series are presented in Table S 3 – S 4. The paratypes ( WII ADR 1210, ZSI -R-29479 ) closely resemble the holotype in overall morphology, with the following distinctions. Paratype WII ADR 1210 has three scales posteriorly connected to the first pair of chin shield; series of seven enlarged, keeled scales on the snout form an inverted “ Y ” - shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scale on either side is oriented diagonally towards the superciliary ridge; paravertebral region rusty brown coloured varied from that of holotype in preservation; ventral region with dark creamish brown to dark brown colours bordering the flank region; scattered dark brown spots on the mental region. Paratype ZSI -R-29479 has two scales posteriorly attached to the first pair of chin shield; scattered dark brown spots on the mental region; series of seven enlarged, keeled scales on the snout form an inverted “ Y ” - shaped pattern, with the first three anterior scales aligned along the midline and pointed posteriorly, posterior to the third scale, two scales on either side is oriented diagonally towards the superciliary ridge; ventral part of the thigh and tail with distinct brown patch scattered.

Colouration in life.

Dorsal and lateral colour variable (Fig. 13 ). Head pale-brown or dark-brown with intermixed pale-yellow scales, some scales with golden yellow keel; three light bands on dorsal surface of head, first concaved, second one diffused and third on interorbital space continuing to supraciliary scales; these bands varies from pale-brown to pale-greenish; lateral sides of head brown to dark-brown, paler towards lips; alternative dark-brown and pale-brown / pale-green streaks radiating from eyes; a dark streak from eye directing towards angle of jaw; lateral side of neck and trunk pale-yellowish brown to pale-green with dark-brown reticulation; lateral side of trunk may be rusty brown without reticulation in some individuals; dorsal surface of back brown with enlarged dark-brown or rusty brown patches; limbs on top dark-brown with pale-brown narrow irregular lines; tail with alternative broad dark-brown and comparatively pale-brown patches on dorsal surface; mental and ventral region creamish brown with ground colour on gular very pale-brownish white or bluish white with three broad dark-blue stripes separated by narrow light lines.

Colouration in preservatives.

Dorsal and lateral head light rusty brown; greyish cross band on interorbital region; nostril and labials greyish speckled; radiating lines around the orbit dark greyish; an oblique streak from posterior margin of orbit indistinct greyish color; lateral region of neck and body greyish colored; paravertebral region same as head; thigh and upper arm rusty brown; crus and lower arm with greyish blotches; digits with dark bands; mental light brownish cream to cream towards the gular with speckles; gular on the midline creamish white with dark streaks on the inner side of folds; ventral side of forelimb, hindlimb and body brownish cream with speckles throughout; tail rusty brown with greyish patch and indistinct light bands (Fig. 12 ).

Sequence divergence.

Ptyctolaemus siangensis sp. nov. has high genetic divergence with its sister species P. gularis 13.9–16.0 %. With other members of the genus, P. siangensis sp. nov. has 23.8–26.3 % genetic difference (Table 5 ).

Etymology.

The specific epithet is a toponym derived from the name of the river “Siang” in the state of Arunachal Pradesh.

Common name.

Siang green fan-throated lizard

Natural history and distribution.

The holotype was found roosting on a branch of a small tree around two metres above the ground, alongside a fast-flowing hill stream at Rottung. One individual was recorded along roadside vegetation in Potin (Fig. 11 C ). This species is currently known from west of Siang River and north of Brahmaputra valley in Arunachal Pradesh. We recorded the species at Rottung, Mouling National Park to Tuting in Adi hills, Potin to Eaglenest Wildlife Sanctuary in the western Arunachal Pradesh, Nameri Tiger Reserve in Assam. In addition, the published sequence from Medog, China is nested within P. siangensis samples. Thus, this species also occurs in Medog, China. The report of P. gularis from Royal Manas National Park, Bhutan ( Das et al. 2016) is most likely of P. siangensis sp. nov. but requires further verification.

Figures

Figure 7. Gular fold arrangement in males of the three species of Ptyctolaemus found in India. Ptyctolaemus gularis A WII - ADR 3477, B WII - ADR 3180, C WII - ADR 3482, D WII - ADR 1436; P. siangensis sp. nov., E WII - ADR 1210, F ZSI - R- 29479, G WII - ADR 1176, H WII - ADR 2542 and P. namdaphaensis sp. nov., I WII - ADR 3283, J WII - ADR 3178, K. WII - ADR 3061, L ZSI - R- 29481. Scale bar = 10 mm.

Figure 11. Habitat of Ptyctolaemus species in northeast India. A, B Habitat of P. gularis in Shillong, Khasi Hills, Meghalaya; C habitat of P. siangensis sp. nov. at Potin, Arunachal Pradesh; D habitat of P. namdaphaensis sp. nov. at Kamala valley, Namdapha Tiger Reserve, Arunachal Pradesh.

Figure 12. Holotype of P. siangensis sp. nov. (WII - ADR 1176) in preserved condition. A Dorsal, B ventral and C lateral views of the body and D – E lateral, dorsal and ventral views of the head. Scale bar = 10 mm.

Figure 13. Ptyctolaemus siangensis sp. nov. showing variation in gular and / or body colouration; A, B Male (ZSI - R- 29479) from Adi hills, Arunachal Pradesh; C, D female (WII - ADR 465) from Potin, Arunachal Pradesh; E, F an uncollected male from Nameri National Park, Assam.