Raorchestes arunachalensis, 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 arunachalensis sp. nov.

Figure 41; Tables 1, 2, S 12

Chresonymy.

Ixalus tuberculatus — Annandale (1912): 7, 17

Ixalus annandalei — Annandale (1912): 7, 16 (spelling error)

Raorchestes annandalii — Ohler et al. (2018): 282, 286

Holotype.

An adult male ( WII-ADA 1553 ) collected by BB on 17 June 2022 from Rengging village ( 28.14136°N, 95.27059°E, elevation 470 m a. s. l.), East Siang District, Arunachal Pradesh, India .

Paratype.

An adult male ( WII-ADA 1554 ) collected along with holotype from the same locality .

Referred material.

Two adult females ( WII-ADA 676 , WII-ADA 677 ) and four subadult males ( WII-ADA 491 , WII-ADA 678 , WII-ADA 680 and WII-ADA 681 ) collected by BB and AD on 17 October 2019 from Potin ( 27.34786°N, 93.84970°E, elevation 580 m a. s. l.), Lower Subansiri District, Arunachal Pradesh ; one subadult ( WII-ADA 1712 ) collected by BB on 29 October 2021 from Balek village ( 28.06245°N, 95.27216°E, elevation 520 m a. s. l.), East Siang District, Arunachal Pradesh ; two adult males ( WII-ADA 1308 and WII-ADA 1327 ) collected by BB and AD on 12 May 2022 near Deban ( 27.49662°N, 96.38949°E, elevation 380 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; two adult males ( WII-ADA 1336 , WII-ADA 1345 ) collected by BB VJ and AD on 13 May 2022 from Motijheel trail ( 27.48690°N, 96.33134°E, elevation 660 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; two adult males ( WII-ADA 1551 and WII-ADA 1552 ) collected by BB on 16 June 2022 from Rottung ( 28.14113°N, 95.15619°E, elevation 390 m a. s. l.), East Siang District, Arunachal Pradesh ; two adult males ( WII-ADA 1549 and WII-ADA 1550 ) collected by BB, KB and DSG on 29 June 2022 near Sessa ( 27.10079°N, 92.53770°E, elevation 1030 m a. s. l.), West Kameng District, Arunachal Pradesh ; four adult males ( WII-ADA 1704 – WII-ADA 1707 ) collected by BB on 8 August 2022 near Mehao nallah ( 28.15436°N, 95.90596°E, elevation 930 m a. s. l.), Mehao Wildlife Sanctuary, Lower Dibang Valley District, Arunachal Pradesh ; one adult male ( WII-ADA 3203 ) collected by RNV and SD on 2 May 2023 from Deban ( 27.49284°N, 96.38569°E, elevation 490 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; one adult male ( WII-ADA 3215 ) collected by RNV and SD on 10 May 2023 from Hornbill ( 27.53810°N, 96.44037°E, elevation 660 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; one adult male ( WII-ADA 3250 ) collected by AD, RNV, SD and JDG on 25 May 2023 from 70 mile ( 27.38734°N, 96.78273°E, elevation 870 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; one adult male ( WII-ADA 3265 ) collected by AD, RNV, SD and JDG on 29 May 2023 from Kamala Valley ( 27.46148°N, 96.42758°E, elevation 650 m a. s. l.), Namdapha Tiger Reserve, Arunachal Pradesh ; one subadult ( WII-ADA 2537 ) collected by KB on 27 August 2022 from Sessni ( 27.04747°N, 92.41797°E, elevation 1260 m a. s. l.), West Kameng District, Arunachal Pradesh ; one subadult ( WII-ADA 2548 ) collected by KB on 28 August 2022 from Khellong ( 27.01314°N, 92.41408°E, 800 m a. s. l.), West Kameng District, Arunachal Pradesh .

Diagnosis.

A medium sized Raorchestes, SVL 19.6–26.3 mm in adult males and SVL 22.3–27.7 mm in adult females; vomerine teeth absent; snout rounded to subovate in dorsal view; nostril closer to snout tip than eye; inter-upper eyelid width less than eye length; nuptial pad present on first finger in males; numerous tubercles on head, dorsum and limb intermixed with spinules; prominent bluntly conical tubercles on upper eyelid; a broad dark brown “ X ” marking on dorsum extending to groin; broad dark brown crossbars on forelimb and hindlimb.

Description of the holotype.

Holotype well preserved except for an incision on underside of right thigh. Medium sized Raorchestes , adult male with vocal sac, 24.8 mm in SVL; head length nearly equal to width ( HL / HW = 0.97); snout sub-oval in dorsal view, truncated in lateral view, slightly protruding beyond lower jaw in ventral view; snout slightly depressed dorsally at internarial region; snout length less than eye length ( SL / EL = 0.81); canthus rostralis distinct, obliqued; loreal region slightly concave; narial region protruding; nostril oval, laterally positioned and obliquely oriented; nostril equidistant between eye and snout tip; internarial distance less than inter-upper eyelid width ( IN / IUE = 0.85) and equal to upper eyelid width; eye moderate in size, less than half of head length ( EL / HL = 0.45); tympanum distinct, rounded less than one fourth of eye length; supratympanic fold distinct; vomerine teeth absent; choanae rounded; tongue posteriorly notched; trunk dorso-ventrally flattened, its length nearly half of snout-vent length ( AG / SVL = 0.49).

Forelimbs slender, forearm length nearly equal to hand length ( FAL / HAL = 0.94); relative length of fingers = FI <FII <FIV <FIII; fingers with rounded disc; disc on fourth finger widest and wider than tympanic diameter ( HTYD /FIVD = 0.63); circum-marginal groove present on discs; palmar tubercles indistinct; subarticular tubercles distinct and rounded, proximal subarticular tubercle on third and fourth fingers smaller than distal ones; enlarged finely granular nuptial pad present on first finger; webbing between fingers absent.

Hindlimbs slender, thigh slightly longer than tibia ( TBL / TL = 0.96) and more than half of the snout-vent length ( TL / SVL = 0.54); relative length of toes = TI <TII <TIII <TV <TIV; each toe with rounded disc; disc as wide as finger disc; circum-marginal groove present on each disc; elongated metatarsal tubercle present; outer metatarsal tubercle absent; webbing moderate, reaching second subarticular tubercle of fourth toe.

Skin on dorsal aspect of snout and anterior part of head smooth with scattered tubercles; prominent tubercles on upper eyelid; posterior part of the head with dense spinules intermixed with blunt slightly large tubercles; scattered tubercles below loreal region and few prominent tubercles on mandibular region; numerous spinules on dorsum and flank; blunt tubercles scattered among spinules on flank; forelimbs smooth dorsally; hindlimbs smooth dorsally with scattered blunt tubercles; on ventral aspect of throat and chest smooth; abdomen and thigh granular; tibia smooth; tubercles on ventro-lateral aspect of tarsus and forearm.

Colouration in life.

Dorsal aspect of head, dorsum, limbs greyish brown; indistinct light bar with darker edge present on inter-upper eyelid space a broad dark brown “ X ” mark on dorsum, posterior ends of this marking extending to groin where it is darker; dark brown stripe along supratympanic fold covering tympanum; broad dark stripe on upper jaw ventral to eye; narial region dark brown; a broad dark brown band on forearm, one on base of the hand and one on each third and fourth finger; three broad dark brown crossbars on thigh and tibia; one similar bar on each tarsus and base of foot; irregular dark brown patches on top of foot and toes; dark brown patches on lateral aspect of thigh; enlarged dark brown patch around vent; on ventral aspect of lower jaw, chest, abdomen and limbs whitish; brown mottling along lower jaw; pale yellowish patches on gular area and base of lower arm.

Colouration in preservative.

Dorsal aspect of head and dorsum brown; upper eyelid dark grey; markings on head, dorsum and limbs visible as in life; forearm, thigh, and tibia paler than dorsum; hand, tarsus, and foot pale cream coloured dorsally; on ventral aspect, head, abdomen, and limbs pale cream coloured with brown mottling; mottling dense on lower jaw and outer ventro-lateral aspect of forearm.

Sexual dimorphism and morphological variation.

Males have a pair of internal vocal sac opening on the lower jaw, an external sub gular vocal sac and an enlarged nuptial pad on the first finger. Morphometric variations among the individuals are given in Table S 12. Live colouration varies among individuals; dorsal colour varies as pale yellowish brown, pale brown or greyish brown. Dorsal marking on head, back and limbs may be faint or distinct; paratype ( WII-ADA 1554 ) has pronounced tubercles on head, dorsum, forelimb, and hindlimbs; intensity of spinules on dorsum varies moderate to heavy; some individuals have pair of concave dark stripes on dorsum instead of “ X ” mark; an inverted triangular mark on head present in some individuals; a distinct or indistinct white bar on inter-upper eyelid space may be present; WII-ADA 1308 have a broad white bar across interorbital space covering anterior half of the upper eyelids.

Morphological comparison.

Raorchestes arunachalensis sp. nov. differs from R. andersoni by presence three broad crossbars on thigh and tibia (vs. single broad band on thigh and tibia); it differs from R. annandalii by presence of dense tubercles on dorsum (vs. skin on dorsum smooth or nearly smooth); it differs from R. barakensis sp. nov. by presence of white and dark brown patches or dark brown patch on yellow background (vs. brown patch on groin present); it differs from R. boulengeri sp. nov. by large body size in adult males, SVL 19.6–26.3 mm in adult males (vs. SVL 17.5–19.1 mm in adult males), by nostrils being closer to snout tip than eye (vs. nostrils equidistant between eye and snout tip); it differs from R. dibangensis sp. nov. and R. eaglenestensis sp. nov. by presence of white and dark-brown patches or dark-brown patch on yellow background on groin (vs. no marking on groin); it differs from R. cinerascens , R. dulongensis , R. hekouensis , R. hillisi , R. leiktho , R. malipoensis , R. mindat , R. parvulus by larger body size, SVL 19.6–26.3 mm in adult males (vs. SVL 16.0 mm in R. cinerascens , 15.0–19.0 mm in R. dulongensis , 16.1–17.5 mm in R. hekouensis , 15.9–17.7 mm in R. hillisi , 15.7–15.8 mm in R. leiktho , 14.6–17.7 in R. malipoensis , 16.7–18.3 mm in R. mindat , 17.0– 18.6 mm in R. parvulus ); further the new species differs from R. huanglianshan by snout length being equal to or less than eye length (snout length greater than eye length); it differs from R. jadoh by larger body size in adult males, SVL 19.6–26.3 mm (vs. SVL 13.6–14.0 mm), and inter-upper eyelid width being less than eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. jakoid by snout length being less than or equal to eye length (vs. snout length greater than eye length), and inter-upper eyelid width being less than eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. kempiae and R. orientalis sp. nov. by presence of white and dark brown patches or dark brown patch on yellow on groin (short brown streak on groin); it differs from R. khonoma sp. nov. by inter-upper eyelid being less than eye length (vs. inter-upper eyelid width equal to eye length); it differs from R. lawngtlaiensis sp. nov. by presence of white and dark brown patches or dark brown patch on yellow on groin (vs. dark brown band with white edge), by presence of three brown crossbars on thigh and tibia (vs. single broad cross bar on thigh and tibia bordered with white spots); it differs from R. leiktho by presence of white and dark brown patches or dark brown patch on yellow on groin (vs. a short brown bar present on groin), by presence of prominent bluntly conical tubercles on upper eyelid (vs. small pointed spinules present on upper eyelid); it differs from R. longchuanensis and R. yadongensis by inter-upper eyelid width being smaller than eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. malipoensis by inter-upper eyelid width being smaller than eye length (vs. inter-upper eyelid width greater than or equal to eye length); it differs from R. mawsynramensis sp. nov. by large body size in adult males, SVL 19.6–26.3 mm in adult males (vs. SVL 16.0– 18.7 mm in adult males); it differs from R. menglaensis by snout length being equal to or smaller than eye length (snout length longer than eye length); it differs from R. monolithus sp. nov. by presence of three crossbars on thigh and tibia (vs. one cross bar on thigh and tibia); it differs from R. nasuta sp. nov. by rounded or sub ovoid snout (vs. snout acute), by presence of white and dark brown patches or dark brown patch on yellow background on groin (vs. yellow patches present on groin); it differs from R. narpuhensis sp. nov. by presence of white and dark brown patches or dark-brown patch on yellow background on groin (vs. no pattern or marking on groin), by dorsum being moderate to heavily tuberculated (vs. scattered tubercles on dorsum); it differs from R. parvulus by presence of dense tubercles on dorsum (vs. scattered tubercles on dorsum), by thigh length being greater than tibia length (vs. thigh length less than or equal to tibia length); it differs from R. rezakhani by presence of white and dark brown patches on groin or dark brown patches on yellow background (vs. a brown short streak on groin); it differs from R. tytthus nov. comb. by snout length being smaller than or equal to eye length (vs. snout length greater than eye length). Raorchestes arunachalensis sp. nov. morphologically close to R. garo , however, tubercles on upper eyelid and behind its much more pronounced than that of R. garo , further the posterior ends of the “ X ” mark on dorsum extends to the groin where it is much darker and broader (vs. dark brown or black marking on groin irregular shaped and sometimes with bright yellow spots). Detailed morphological comparison with the congeners is provided in Table 1. Raorchestes arunachalensis sp. nov. is morphologically very similar to R. shillongensis . However, mean body size ( SVL) of R. arunachalensis sp. nov. (23.57 ± 1.87 mm) is greater than that of R. shillongensis (17.02 ± 1.51 mm). Raorchestes arunachalensis sp. nov. is distributed in north and east of Brahmaputra Valley while R. shillongensis is distributed only in Khasi Hills of Meghalaya.

Phylogenetic relationship and genetic divergence.

Phylogenetically R. arunachalensis sp. nov. has a sister species relationship with an undescribed lineage from Arunachal Pradesh ( UFB 100 , PP 1.0; Figs 2 , 3 ) with genetic divergence of 2–3.6 % in the 16 S, 5.2–9.3 % in the cyt b and 3.9–6.7 % in the COI genes. The genetic divergence with other congeners included in this study is 2.9–7.8 % in the 16 S, 11.8–19.6 % in the cyt b and 7.6–14.3 % in the COI genes (Tables S 7 A – C).

Acoustics.

The calls of Raorchestes arunachalensis sp. nov. were recorded near Deban, Namdapha Tiger Reserve on 12 May 2022 at 19: 10 hrs and at an ambient temperature of 22.4 ° C. The call description is based on 39 calls from a single individual ( WII-ADA 1327 ). The calls are of a single type, non-pulsatile, emitted in groups (2–33 calls per group) at regular intervals (Fig. 40 ). The mean call duration is 23.9 ± 1.78 ms (15–25 ms) with call rise time 1.21 ± 0.41 ms (1–2 ms) and a call fall time of 22.63 ± 1.84 ms (14–24 ms). The mean interval between calls is 137.14 ± 7.24 ms (125–158 ms). The mean dominant frequency is 2752.84 ± 108.94 Hz (2411.7–2842.4 Hz). A detailed comparison of the advertisement calls with those of the congeners is presented in Table 2.

Etymology.

The specific epithet is a toponym derived from the name of the State “ Arunachal Pradesh ” in India where this species is widely distributed across the State.

Suggested common name.

Arunachal bush frog.

Distribution and natural history.

Raorchestes arunachalensis sp. nov. is currently distributed throughout the State of Arunachal Pradesh from West Kameng District in the west, Lower Subansiri District, East Siang District, Mehao Wildlife Sanctuary and Namdapha Tiger Reserve in the east, within an elevation range of 380–1260 m a. s. l. (Figs 25 B , 33 H ).

The holotype and the paratype were recorded on shrub at a perch height of approximately two meters above ground in dense bushy thickets; calling individuals were observed on a hillside near a cultivated area in Rottung; in Sessa, we observed calling individuals along roadside vegetation while it was drizzling; calling males were found on shrubs at a height of about one metre above the ground in Mehao Wildlife Sanctuary; in Namdapha Tiger Reserve, we found calling males on woody shrubs upto three meter height along hill slope and near streams. Other sympatric species recorded with this species are R. barakensis sp. nov., R. orientalis sp. nov., Amolops sp. , Alcalus fontinalis Boruah et al., 2023 , Gracixalus patkaiensis Boruah et al., 2023 , Xenophrys ancrae ( Mahony, Teeling & Biju, 2013) and Limnonectes sp. in Namdapha Tiger Reserve; Kurixalus naso ( Annandale, 1912) , Theloderma cf. baibungense , Amolops sp. , Ingerana borealis ( Annandale, 1912) in Abor hills.

Remarks.

Annandale (1912) most likely reported this species as “ Ixalus tuberculatus ” (= R. andersoni ) based on morphology (Fig. S 1). However, the type locality of R. andersoni is in Yunnan, China, approximately 300 km northwest of the nearest locality of R. arunachalensis sp. nov. in Namdapha Tiger Reserve, Arunachal Pradesh (see comments on R. andersoni above).

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 25. Distribution of Raorchestes species in northeast India. A Raorchestes rezakhani and four other closely related species; B Raorchestes annandalii and three new species. Type localities are denoted by stars, and other localities are denoted by circles.

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 40. Comparative spectrograms and oscillograms illustrating representative calls of two new 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 41. Raorchestes arunachalensis sp. nov. A – C Holotype (WII-ADA 1553) in preserved condition, A dorsal view, B ventral view, C lateral view of head. D – G WII-ADA 3203 in life from Namdapha TR, D lateral view, E ventral view, F groin, G posterior view of thigh. H Dorsolateral and I ventral view of WII-ADA 678 in life from Potin. J Dorsolateral view of holotype in life. K Paratype (WII-ADA 1554) in life. L Dorsolateral view of WII-ADA 1549 from Sessa in life. M Dorsolateral view of WII-ADA 1705 from Mehao WLS in life. Inset image showing dense tubercles on dorsum in A, distinct blunt tubercles in D, granular skin on abdomen in I. Scale bar = 10 mm.