Raorchestes monolithus, Boruah & Deepak & Das, 2025

Boruah, Bitupan, Deepak, V. & Das, Abhijit, 2025, Revision of bush frogs, Raorchestes and Philautus (Amphibia: Anura: Rhacophoridae) from the northeast Indian biodiversity hotspot with description of thirteen new species, Vertebrate Zoology 75, pp. 517-625 : 517-625

Raorchestes monolithus sp. nov.

Figure 37; Tables 1, 2, S 12

Holotype.

WII-ADA 1634 , an adult male collected by BB on 21 July 2022, from 1.5 km northeast of Pumdunlong village ( 25.50014°N, 94.00156°E, elevation 1496 m a. s. l.), Senapati District, Manipur, India .

Paratypes.

Five adult males ( WII-ADA 1632 , WII-ADA 1633 , WII-ADA 1635 – WII-ADA 1637 ) collected along with the holotype from the same locality .

Diagnosis.

Small sized Raorchestes, SVL 17.9–20.6 mm in male; female unknown; head wider than long ( HL / HW = 0.89–0.97); snout rounded, its length equal to or slightly less than eye length ( SL / EL = 0.89–1.0); snout length equal to inter-upper eyelid width; tympanum indistinct; nostril equally positioned between eye and snout tip; internarial distance greater than upper eyelid width ( UEW / IN = 0.67–0.89); a broad light brown and anteriorly diffused patch present on groin and a large whitish patch ventral to it; single crossbar on tibia and thigh.

Description of the holotype.

Adult male with vocal sac, 20 mm in SVL; head length nearly equal to width ( HL / HW = 0.97); snout rounded in dorsal view and lateral view, slightly protruding lower jaw in ventral view, snout length less than half of head length ( SL / HL = 0.38) and equal to eye length ( SL / EL = 1); nostril oval, laterally positioned, nearly equidistant between eye and snout tip ( NS / EN = 0.92); internasal distance less than inter-upper eyelid distance (INS/ IUE = 0.84) and greater than upper eyelid width ( UEW /INS = 0.76); inter upper eyelid distance greater than upper eyelid width ( UEW / IUE = 0.64); eye length less than half of the head length ( EL / HL = 0.38); loreal region slightly concave, canthal ridge rounded; tongue cordiform; vomerine teeth absent; choanae round; pair of internal slit like openings on lower jaw; symphysial knob present on lower jaw; tympanum round, touches supratympanic fold, tympanic diameter one third of eye length ( HTYD / EL = 0.32); supratympanic fold distinct; external large subgular vocal sac present; trunk length nearly half of SVL ( AG / SVL = 0.44).

Forelimb slender; forearm slightly shorter than hand length ( FAL / HAL = 0.91); third finger longest, relative length of fingers = I <II = IV <III; finger with rounded disc, disc width of finger III and IV greater than tympanic diameter; discs with circum-marginal groove; subarticular tubercles large and rounded, lower subarticular tubercles on finger III and IV indistinct; palmar tubercle indistinct; fine granular nuptial pad on first finger; webbing between fingers absent.

Hindlimb slender; thigh longer than tibia ( TBL / TL = 0.89); thigh length nearly half of SVL ( TL / SVL = 0.47); tibia length less than half of SVL ( TBL / SVL = 0.42) and nearly equal to foot length ( FOL / TBL = 0.94); fourth toe longest, relative length of toes = I <II <V <III <IV; toe with rounded disc, disc width of toe IV widest and wider than tympanic diameter; disc with circum-marginal groove; subarticular tubercles round, proximal subarticular tubercles on the outer three toes indistinct; supernumerary tubercles absent; inner metatarsal tubercle elongated, outer metatarsal tubercle absent; webbing slight, not reaching second subarticular tubercle of the fourth toe.

Skin on dorsal aspect of head smooth, upper eyelid and below inter-upper eyelid space shagreened; tubercles on upper eyelid and posterior part of the head barely visible; two tubercles posterior to angle of jaw on each side; few tubercles scattered on dorsum and dorsal aspect of limbs, tubercles on anterior dorsum prominent than that of posterior dorsum; flank with distinct tubercles scattered; flank ventro-laterally granular; throat and chest nearly smooth, granules barely visible; abdomen granular; ventral aspect of thigh indistinctly granular; tibia smooth.

Colouration in life.

Dorsal aspect of head and dorsum pale yellowish brown, becoming paler towards flank when compared to dorsal side; irregular white spots on both upper and lower jaws; supratympanic fold pale yellow; lower arm pale yellow; faint crossbar on forearm; similar crossbar on thigh and tibia; faint brown stripe on groin, anteriorly diffused and directing antero-dorsally; enlarged pale white patch below the brown stripe on groin; pale white patch on thigh near groin; faint white patches on axilla; disc on finger and toe yellow; chin and gular region pale yellowish; irregular white mottling on abdomen and ventral aspect of thigh.

Colouration in preservative.

Dorsally pale brown; upper eyelid dark grey; greyish brown patch on posterior part of head; loreal region slightly darker; slightly dark brown irregular patches on dorsum above forelimb insertion, middle and posterior part of dorsum; dorsal aspect forelimb and hindlimb slightly paler than dorsum; brown cross bar on forearm and base of the hand; similar single crossbar on each tibia; cross bar on thigh faint; base of feet and toe with faint crossbars; on ventral aspect of head, trunk and limbs cream coloured with brown speckling.

Morphological variation.

Detailed morphological variations are provided in Table S 12; dorsal brown patches vary among type series; tubercles on head, upper eyelid and dorsum much pronounced, crossbars on limbs prominent, and dorsal colour darker in WII-ADA 1635 than holotype and other paratypes; WII-ADA 1633 has distinct tubercles on head and upper eyelid.

Morphological comparison.

Raorchestes monolithus sp. nov. differs from R. andersoni by position of nostril equidistant from eye and snout tip (vs. nostril much closer to snout tip than eye), absence of yellowish band on inter-upper eyelid space (vs. a pale yellow band between eyes followed by two more bands at least in some individuals); it differs from R. annandalii by snout length being equal to inter-upper eyelid width (vs. snout length greater than inter-upper eyelid width); it differs from R. barakensis sp. nov. by absence of bony projection on humerus (vs. a bony projection present on humerus protruding ventrally), scattered tubercles on dorsum (vs. dense spinules on dorsum); it differs from R. boulengeri sp. nov. by absence of “) (” on dorsum (vs. present), by presence of spinules on head, upper eyelids and dorsum sparsely (vs. spinules comparatively dense); it differs from R. cinerascens nov. comb. by presence of single crossbar on thigh and tibia (vs. three crossbars on thigh and tibia); it differs from R. dibangensis sp. nov. by head being wider than its length (vs. head length equal to its width), by inter-upper eyelid being width equal to eye length (vs. inter-upper eyelid width less than eye length), nostril being equidistant between eye and snout tip (vs. nostril closer to snout tip than eye); it differs from R. dulongensis by presence of nuptial pad on first finger of males (vs. nuptial pad absent), tympanum indistinct (vs. tympanum distinct), “) (“ marking on dorsum absent (vs. a dark “) (“ marking on dorsum present); it differs from R. garo by dorsal colour pattern, absence of dark patch on dorsum, absence of white bar on inter-upper eyelid space, and absence of mid dorsal line (vs. dorsal colour in R. garo variable, enlarged dark patch on dorsum may be present, mid dorsal line may be present, white bar on interorbital space may be present), by presence of a brown patch and pale white patch below it on groin (vs. dark brown enlarged patch with whitish or yellowish patches on groin), and by absence of dark patch on lateral aspect of thigh (vs. dark brown patch with or without yellow spots present on lateral aspect of thigh); it differs from R. hekouensis and R. malipoensis by its larger body size in males, SVL 17.9–20.6 mm (vs. SVL 16.1–17.5 mm in males of R. hekouensis and SVL 14.6–17.7 mm in males of R. malipoensis ), tympanum indistinct (vs. tympanum distinct), and “ X ” shaped mark absent on dorsum (vs. distinct “ X ” shaped marking on dorsum); it differs from R. hillisi by larger body size in males, SVL 17.9–20.6 mm (vs. SVL 15.9–17.7 mm in males), by head being wider than long (vs. head longer than wide), by snout length being equal to or slightly less than eye length (vs. snout length longer than eye length), tympanum indistinct (vs. tympanum distinct), absence of dark stripes on dorsum (vs. a dark “) (“ shaped marking on dorsum); it differs from R. huanglianshan by snout length equal to or slightly less than eye length (vs. snout length greater than eye length), tympanum indistinct (vs. tympanum distinct), absence of dark marking on inter-upper eyelid space (vs. a brown triangular marking on inter-upper eyelid space), and by absence of “ X ” mark on dorsum (vs. a dark “ X ” mark on dorsum); it differs from R. jadoh and R. jakoid by snout length equal to inter-upper eyelid width (vs. snout length greater than inter-upper eyelid width), by nostril being equidistant between snout tip and eye (vs. nostril closer to snout tip than eye), and thigh length being greater than tibia length (vs. thigh length less than tibia length); it differs from R. kempiae by snout length being equal to inter upper eyelid width (vs. snout length greater than inter-upper eyelid width), inter-upper eyelid width being equal to eye length (vs. inter upper eyelid width smaller than eye length); it differs from R. lawngtlaiensis sp. nov. by inter upper eyelid width being equal to eye length (vs. inter upper eyelid width greater than eye length), internarial distance being greater than upper eyelid width (vs. internarial distance equal to upper eyelid width); it differs from R. leiktho by larger body size in adult males, SVL 17.9–20.6 mm (vs. SVL 15.7–15.8 mm); it differs from R. longchuanensis by smaller body size in males, SVL 17.9–20.6 mm (vs. SVL 21.4–23.9 mm in males), by inter upper eyelid width being equal to eye length (vs. inter upper eyelid width greater than eye length), tympanum indistinct (vs. distinct); it differs R. mawsynramensis sp. nov. by dorsal skin smooth with few scattered spinules on it (vs. dense spinules on dorsum), absence of “) - (“ on dorsum (vs. present), marking absent on inter-upper eyelid space absent (vs. present); it differs from R. menglaensis by head being wider than long (vs. head longer than wide), snout length being equal to or slightly less than eye length (vs. snout length longer than eye length) ,, no “ X ” shaped marking on dorsum (vs. a “ X ” marking on dorsum present), tympanum indistinct (vs. tympanum distinct); it differs from R. mindat by absence of black and white patches on groin (vs. enlarged black and white patches present on groin), by absence of white patches on lateral aspect of thighs (vs. enlarged white patches on lateral aspect of thighs); it differs from R. narpuhensis sp. nov. by presence of brown patch with white crown shaped patch below it on groin (vs. groin yellowish without dark or light patches), and by position of nostril equidistant from eye and snout tip (vs. nostril closer to snout tip than eye); it differs from R. nasuta sp. nov. by rounded snout (vs. acute snout), by head being wider than long (vs. head longer than its width), and snout length being equal to inter-upper eyelid width (vs. snout length being greater than inter upper eyelid width); it differs from R. orientalis sp. nov. by scattered tubercles on dorsum (vs. dense spinules on dorsum), darker stripes on dorsum barely visible or absent (vs. concave dorsal stripes distinct); it differs from R. parvulus by absence of inter-upper eyelid bar and stripes on dorsum (vs. bar or triangular mark between upper eyelids and “) (“ mark on dorsum present), tympanum indistinct (vs. tympanum distinct); it differs from R. rezhakhani by absence of concave stripes on dorsum (vs. a “) (“ or “) - (“ mark on dorsum), by presence of single crossband on thigh and tibia (vs. three crossbands on thigh and tibia); it differs from R. shillongensis by absence of stripe or blotch on dorsum (vs. dorsal colour variable, distinct or indistinct “) (“ mark or dark hourglass shaped mark may be present); it differs from R. tytthus nov. comb. by position of nostril equidistant from eye and snout tip (vs. nostril closer to snout tip than eye), by snout length being equal to eye length (vs. snout length longer than eye length), absence of “) (“ marking on dorsum (vs. a “) (“ mark on dorsum); it differs from R. yadongensis by inter-upper eyelid width being slightly less than or equal to eye length (vs. inter-upper eyelid width greater than eye length), absence of triangular mark between upper eyelids (vs. distinct dark triangular marking between upper eyelids), tympanum indistinct (vs. tympanum distinct). Detailed morphological comparison with other congeneric species included in this study is provided in Table 1.

Acoustics.

The calls of R. monolithus sp. nov. were recorded in Pumdunlong, Manipur on 21 July 2022 at 18: 50 hrs at an ambient temperature of 21.6 ° C. The call description is based on 70 calls from two individuals ( WII-ADA 1634 and WII-ADA 1635 ). The calls are single type, non-pulsatile (Fig. 31 ) and are emitted in groups (5–13 calls per call group). In each call group, the amplitude peaks after the initial 1–3 calls. The mean call duration is 22.01 ± 16.07 ms (12–29 ms) with a call rise time of 1 ms and call fall time of 18.52 ± 4.62 (11–28 ms). The intercall interval is 164.78 ± 25.14 ms (118–285 ms). The mean dominant frequency is 3470.51 ± 59.77 Hz (3316.1–3531.4 Hz). A detailed comparison of advertisement calls with those of the congeners is presented in Table 2.

Phylogenetic relationship and genetic divergence.

Raorchestes monolithus sp. nov. is sister to R. shillongensis and R. jadoh with strong nodal support ( UFB 100 , PP 1.0; Figs 2 , 3 ). The genetic divergence with other congeners included in this study is 3.9–8.6 % in the 16 S, 11.8–18.2 % in the cyt b and 6.5–13.8 % in the COI genes (Table S 7 A – C).

Etymology.

This species is named after the “monoliths” located in Willong Khullen village in Manipur State, 4 km southwest from the type locality of this species.

Suggested common name.

Willong-Khullen bush frog.

Distribution and natural history.

Raorchestes monolithus sp. nov. is known only from its type locality and around Willong Khullen Village in Manipur (Fig. 19 B ). Calling individuals were recorded between 18: 00–20: 00 hrs on shrubs and small woody vegetation at perch heights of ~ 2 m. Calling aggregations were recorded in secondary forests at various degradation state (Fig. 33 D ). We observed breeding aggregation of Hyla annectans ( Jerdon, 1870) in the same habitat in temporary water puddles.

Figures

Figure 2. A, B Maximum likelihood tree inferred from the concatenated data set (16 S, cyt b, COI and RHO) for Raorchestes species from northeast India, Indo-Burma and Indo-China. Outgroups are not shown in this tree. Numbers at the internal branches represent ultrafast bootstrap values (UFB). Values below 50 are not shown. Scale bar: substitutions per site.

Figure 3. A, B Bayesian tree inferred from the concatenated data set (16 S, cyt b, COI and RHO) for Raorchestes species from northeast India, Indo-Burma and Indochina. Outgroups are not shown in the tree. Numbers at the nodes represent posterior probability (PP) value. Values <0.5 are not shown. Scale bar: substitutions per site.

Figure 19. Distribution of Raorchestes species in northeast India. A Raorchestes garo and three others closely related new species; B Raorchestes kempiae, R. shillongensis, R. mindat and three new species. Type localities are denoted with stars.

Figure 31. Comparative spectrograms and oscillograms illustrating representative calls of three species of Raorchestes. A, B Oscillograms, C spectrogram, D power spectrum. The call marked with an arrow on top in A is expanded in B.

Figure 33. Habitat at the type localities of Raorchestes species in northeast India. A Lowland forest stream at the type locality of R. lawngtlaiensis sp. nov. in Ngengpui WLS; B landscape view of Mehao WLS from Abango, type locality of R. dibangensis sp. nov. in Abango; C. hill stream and riparian habitat at the type locality of R. shillongensis in Malki, Shillong; D landscape view of the hills at Pumdunlong, the type locality of R. monolithus sp. nov. at Willong Khullen Village; E landscape view of hills and lowland areas at Khonoma, the type locality of R. khonoma sp. nov.; F forest cover at Bompu, Eaglenest WLS at the type locality of R. eaglenestensis sp. nov.; G hill stream and forest cover at Abor hills, habitat of R. magnus sp. nov.; H landscape view of Abor hills and adjacent lowland areas, habitat of R. arunachalensis sp. nov.

Figure 37. Raorchestes monolithus sp. nov. A Dorsal and B ventral view of holotype (WII-ADA 1634) in preserved condition. C Dorsal and D ventral view of paratype (WII-ADA 1635) in preserved condition. E Holotype in life; F paratype (WII-ADA 1637) in life. Scale bar = 10 mm.