Megophrys (Xenophrys) numhbumaeng, Mahony & Kamei & Teeling & Biju, 2020

Mahony, Stephen, Kamei, Rachunliu G., Teeling, Emma C. & Biju, S. D., 2020, Taxonomic review of the Asian Horned Frogs (Amphibia: Megophrys Kuhl & Van Hasselt) of Northeast India and Bangladesh previously misidentified as M. parva (Boulenger), with descriptions of three new species, Journal of Natural History 54 (1 - 4), pp. 119-194 : 157-162

Megophrys (Xenophrys) numhbumaeng sp. nov.

Holotype. Adult male ( BNHS 6075 [field tag SDBDU 2007.041 ]: Figures 10 , 11 (a,b)), from a waterfall (25.047500, 93.434444, 915 m asl.), approx. 7 km before reaching Aziuram village coming from Tamenglong town , Tousem subdivision, Tamenglong district, Manipur state, Northeast India, collected by RGK on 7 May 2007.

Paratype. One adult male ( BNHS 6076 [field tag SDBDU 2007.042 ] Figure 11 (c,d)), from Aziuram village (25.023333, 93.410000, 1010 m asl.), Tousem subdivision, Tamenglong district, Manipur state, Northeast India, collected by RGK on 5 May 2007 .

Holotype description (measurements in mm). Mature male ( SVL 34.6) ( Figures 10 , 11 (a,b)). Head small, longer than wide ( HW 12.5, HL 13.8, IFE 6.3, IBE 10.7); snout bluntly pointed in dorsal view, obtusely protruding in lateral view, rostral

appendage absent ( Figure 10 (c)); loreal region vertical and concave; canthus rostralis angular; dorsal region of snout slightly concave; eye length more than two times longer than maximum tympanum diameter and slightly longer than snout ( EL 5.3, TYD 2.4, SL 5.0); eye – tympanum distance ( TYE 2.0) less than maximum tympanum diameter; tympanum circular, its upper border concealed by supratympanic ridge ( Figure 10 (c)); pupil in life oval, horizontally orientated when dilated; nostril oval, orientated laterally, closer to eye than snout ( EN 2.2, SN 2.8); internarial distance greater than eyelid width and narrowest point between upper eyelids ( IN 4.3, UEW 3.6, IUE 3.9); pineal ocellus not visible externally; vomerine ridges present, ovoid, weakly raised, with short vomerine teeth, orientated acutely, positioned slightly posterior to choanae, equidistant from each other and choanae; maxillary teeth present; tongue moderately large, cordiform (with weak notch posteriorly), no medial lingual process.

Forelimbs moderately long, thin ( Figure 10 (a,b)), forearms slightly enlarged relative to upper forelimbs, forearm shorter than hand length ( FAL 9.5, HAL 11.1); fingers long, narrow, lateral fringes absent ( Figure 10 (d)), finger length formula I = II <IV < III ( FIL 4.4, FIIL 4.4, FIIIL 8.0, FIVL 5.1); interdigital webbing, and subarticular, supernumerary and palmar tubercles absent; thenar tubercles weak; fingertips rounded, noticeably expanded relative to digit widths, with circular pads, terminal grooves absent on fingertips. Hindlimbs long, thin ( Figure 10 (a,b)); thigh shorter than shank, and longer than foot (TL 19.0, SHL 20.1, FOL 17.9); toes long, rounded, lateral fringes absent ( Figure 10 (e)), relative toe lengths I <II < V < III <IV; toe tips rounded, slightly dilated, with distinct circular pads, terminal groves on toe tips absent; webbing rudimentary; inner metatarsal tubercles weak; outer metatarsal, subarticular, and supernumerary tubercles absent; ridge of callous tissue very weak on ventral surface of all digits.

Skin of dorsal surfaces of body, limbs, and dorsal and lateral surfaces of head smooth to weakly granular; tympanum smooth with borders distinctly raised; upper eyelids each with short, raised ridge; supratympanic ridge narrow anteriorly, expanding moderately posterior to tympanum, extending from orbit in straight line to upper tympanum border, broadly curving obliquely downward along posterior border of tympanum, terminating above forearm insertion on each side ( Figures 10 (c) and 11(a)); flanks with small and scattered tubercles; dorsolateral ridges narrow, well defined, on left side extending from behind supratympanic ridge to ca. 80% trunk length, on right side aberrant and disjunct, extending from above axilla to above groin; weak, ‘ V ’ -shaped parietoscapular ridge present, its two sides extending posteriorly from above tympanum, meeting medially beyond level of axilla; second ridge indicative of right side of typical inverted ‘ V ’ -shaped sacral ridge (as seen on most other M. [ Xenophrys ] species) present on mid-dorsum ( Figure 10 (a)); distinct transverse ridges present on dorsal surface of thighs, and shanks. Gular region, chest, abdomen and ventral surfaces of limbs smooth; pectoral gland small, raised, positioned on level with axilla on each side ( Figure 10 (b)); femoral gland medium-sized, flat, positioned equidistant from knee and cloaca on posterior surface of each thigh; white and black skin asperities present on lower lateral surface of head, on tympanic region and supratympanic ridge (absent on tympanum), they form a moderately dense narrow band circummarginally on ventral surface of mandible, sparse on anterior dorsum, significantly increasing in density posteriorly on dorsum, and on dorsal ridges, absent from all remaining surfaces.

Colour: In preservation ( Figure 10 ): Dorsal and lateral surfaces of head, body, forelimbs and hindlimbs primarily plain, mid-brown; between eyes, a solid dark brown triangular marking containing small darker brown blotches; top of some flank tubercles brownishcream with black lower borders; front of snout and lateral canthus rostralis dark brown with distinct light patch below each nostril and distinct light vertical stripe on anteriormost lateral surface of snout; wide vertical dark brown bar below eyes; dark brown blotch extends from posterior canthus through tympanum to posterior supratympanic ridge on each side; supratympanic ridges light yellowish-cream; single large dark brown blotch on anterior lateral surface of forearms; dorsal surface of outer three fingers laterally with dark brown blotches. Throat, chest and anterior part of abdomen primarily light yellowishgrey, grey colouration diffuses into mottling and blotches posteriorly on abdomen, which is creamish-yellow; broad dark brown stripe extends laterally along abdomen on both sides; small light spots along edge of lower jaw; ventral surface of thighs and shanks creamish-yellow with faint brown mottling and dark brown blotches laterally; ventral surfaces of tarsus and feet dark brown to greyish-brown, inner metatarsal tubercles light grey; area surrounding vent and posterior surfaces of thighs dark brown; forelimbs and hands ventrally mottled creamish-yellow and light greyish-brown; pectoral and femoral glands creamish-white. In life ( Figure 11 (a,b)): Mostly as described in preservation with colours generally richer and with the following additions: dorsum with slightly darker brown mottling not obvious in preservation; groin without contrasting colouration; dorsal ridges of body and limbs orangish-brown; granules on dorsal and lateral surfaces of head, body and limbs with moderately dense orange spots; iris pale orangish-brown; throat, chest and anterior abdomen primarily dark greyish-brown, posterior abdomen pale greyish-white with dark greyish-brown blotches; ventral surfaces of thighs mottled with shades of brown or greyish-brown with sparse tiny white spots.

Variation. See Table 2 for morphometric differences between the holotype and paratype adult males. Additionally, the paratype (BNHS 6076) differs from the holotype by several other characters: toes five and three are subequal in relative length; vomerine teeth appear comparatively smaller; dorsolateral ridges extend almost entire trunk length on each side; scapular ridges absent; white dermal asperities distribution are as described for holotype but are also present on loreal region, posterior surface of eyelids, a few on dorsal tibia, ventral tarsus and on tubercles in cloacal region, sparse on upper flanks, absent on all remaining surfaces; upper eyelids each with a small tubercle as opposed to a short ridge; pectoral glands comparatively larger than on holotype ( Figure 11 (d)); parietoscapular ridge ‘ Y ’ -shaped ( Figure 11 (c)). General markings and colouration in preservation match holotype but ventral markings generally much darker and better defined on paratype ( Figure 11 (d)); light vertical stripe on anterior-most lateral snout surface absent; triangular marking on head without darker speckling, but with light central blotch, and with dark brown stripe extending anteriorly to tip of snout ( Figure 11 (c)); large dark brown blotch on anterior lateral surface of forearms replaced by two short dark brown transverse stripes; colouration in life not documented for paratype.

Secondary sexual characters. This species is currently known from only two male specimens which have the following characters usually unique to males of Megophrys : weakly raised nuptial pads covered with black micro-asperities present, covering most of dorsal surface of base of finger I, narrowing distally and extending onto base of distal phalange on inner dorsal side; nuptial pad small and oval-shaped on finger II, on inner dorsal side of base of digit extending onto proximal phalange; external vocal sac indistinct; internal vocal slits present near rear of lower mandible; forearms slightly enlarged relative to upper forelimbs; fleshy projection above cloaca absent.

Morphological comparisons. Megophrys numhbumaeng sp. nov. (adult males N = 2) differs from the following species that have not yet been assigned to a subgenus or species group through molecular analyses: from M. damrei and M. shuichengensis by much smaller adult male size, SVL 33.8 – 34.6 mm (vs. M. damrei : adult male SVL 47.7 – 57.1 mm, N = 7 [Mahony 2011; Neang et al. 2013]; M. shuichengensis : adult male SVL 102.0 – 118.3 mm, N = 8 [ Tian et al. 2000]); from M. feii by larger adult male size, SVL 33.8 – 34.6 mm (vs. adult male SVL 24.3 – 25.1 mm, N = 4), lateral dermal fringes on toes absent (vs. present), and nuptial pads on fingers of males present (vs. absent) ( Yang et al. 2018).

Megophrys numhbumaeng sp. nov. differs from M. parva s.s. by larger head proportions, HW/SVL 36.1 – 36.4%, HL/SVL 37.0 – 39.9% (vs. HW/SVL 32.1 – 33.9%, HL/SVL 32.1 – 35.1%, N = 4), larger eye proportions, ED/SVL 14.2 – 15.3% (vs. ED/SVL 10.8 – 12.2%, N = 4), and longer shanks on males, SHL/SVL 51.8 – 58.1% (vs. male SHL/SVL 42.8 – 43.7%, N = 2).

Megophrys numhbumaeng sp. nov. differs from Indian species molecularly assigned to the M. (X.) megacephala SG based on the following characters: from M. ancrae by smaller male adult size, SVL 33.8 – 34.6 mm (vs. male SVL 39.1 – 45.0 mm, N = 8), FIL = FIIL (vs. FIL<FIIL), and tympanum circular (vs. oval); from Megophrys awuh sp. nov. by slightly smaller adult male size, SVL 33.8 – 34.6 mm (vs. male SVL 35.7 – 41.1 mm, N = 4), toe tips expanded relative to digit width (vs. not expanded), and dermal asperities forming circummarginal band on lower jaw present (vs. absent); from Megophrys dzukou sp. nov. by narrow lateral ridges on toes absent (vs. present), dorsolateral ridges almost complete trunk length (vs. vary from absent to ~25% trunk length); from M. megacephala by smaller male adult size, SVL 33.8 – 34.6 mm (vs. male SVL 45.9 – 53.4 mm, N = 7), and considerably narrower head HW/ SVL 36.1 – 36.4% (vs. HW/SVL 40.2 – 45.1%, N = 9); from M. oropedion (its genetically closest relative) by longer shanks, SHL/SVL 51.8 – 58.1% (vs. SHL/SVL 41.3 – 49.7%, N = 12), digit tips noticeably expanded relative to digit widths (vs. not expanded), and HW<HL (vs. HL≤HW); from M. serchhipii by smaller male adult size, SVL 33.8 – 34.6 mm (vs. male adult SVL 36.1 – 46.7 mm, N = 25), dorsolateral ridges almost complete trunk length (vs. dorsolateral ridges absent or short if present, extending <40% trunk length), FIIL<FIVL (vs. FIVL≤FIIL), and tympanum circular (vs. oval); from M. zunhebotoensis by slightly larger male adult size, SVL 33.8 – 34.6 mm (vs. adult male SVL 28.4 – 33.9, N = 22), and dorsolateral ridges almost complete trunk length (vs. absent to maximum 80% trunk length), dorsal and lateral surfaces of head posterior to orbits smooth with small and scattered granules (vs. typically more rugose, with small and scattered tubercles, most obvious in life).

Etymology. The specific epithet is treated as a noun in apposition, and the phonetic derivative of a portmanteau word ‘ nwmbwmaeng ’ from the Rongmei (N-ruangmei) language, the dominant tribal language in the Tamenglong district of Manipur state. The word ‘ nwm- ’ means forest, and ‘ bwmaeng ’ means spirit, alluding to the species ’ phantomish nature eluding the field researchers on at least three visits to the locality in the presumably (early) breeding season. For correct pronunciation of the species epithet, ‘ numhbumaeng ’ (pronounced noom-boo-meng) would be the phonetic spelling of the name.

Suggested common name. We suggest ‘ Tamenglong Horned Frog ’ based on the species ’ type locality being in the Manipur state, Northeast India .

Distribution. Known only from two nearby localities between 915 and 1010 m asl. Both localities are near the summit of the second western-most north – south orientated mountain ridge in Manipur state ( Figure 2 ). This range is drained to the west by the Makru (Makhu) River and to the east and south by the Barak (Ahu) River, both of which form deep valleys, below 200 m asl. that may be a significant geographical barrier to dispersal for this species.

Habitat and natural history. The holotype was collected around 19:00 h on a rainless night at the side of a small (~ 1 m wide) seasonal stream at the top of a ~ 10 m high waterfall. The stream was located beside the road between Aziuram and Tamenglong towns. The surrounding habitat is primarily secondary forest consisting of bamboo and broad-leaved trees, with a moderately dense undergrowth of herbaceous vegetation and three to four small rocky streams flowing into the waterfall.

Remarks. This species is the sister taxon of the mid to high-elevation species M. oropedion ( Figures 1, S1 & S 3 ; Mahony et al. 2017: figs. 1 & 3 [as “ M. cf. oropedion ”]; Mahony et al. 2018: fig. 4 [as “ M. cf. oropedion ”]) which is currently endemic to Meghalaya state above 1115 m asl. The nearest collection locality for M. oropedion is in the vicinity of Shillong town, ca. 165 km NW of Aziuram village. Molecular dating analyses suggested that these sister species split from their most recent common ancestor at ca. 2.5 MY ( Mahony et al. 2017, fig. 1). Efforts were made by RGK in July 2015 to collect additional specimens of this species from the type locality and vicinity of the waterfall, without success, despite being the presumed breeding season with plenty of monsoonal rains. This species is sympatric with M. serchhipii at Aziuram village where both species have been collected from streams at similar elevations. Further field collections from western Manipur would be necessary to understand the elevation and distribution limits of this species.

Figures

Figure 1. ML phylogenetic tree of the subgenus Megophrys (Xenophrys) based on the concatenated mt +nuDNA alignment. Bootstrap values ≥95% are represented by a black spot; 80–95% represented by a grey spot; <80% not given. Numbers next to species names correspond with specimen numbers in Table 1.

Figure 2. Topographic distribution map of the Megophrys (X.) megacephala SG taxa: Left. All taxa from Northeast India and surrounding countries: diamonds represent type localities; circles represent referred localities based on examined specimens; circles with central dot represent identifications based on literature where sufficient evidence was available (see Remarks sections); Right. Inset rectangle enlarged to show the distributions of species from more densely sampled southern Nagaland and northern Manipur states, Northeast India. Blue lines represent major rivers; grey lines represent international borders.

Figure 3. Megophrys parva adult male paralectotype (BMNH 1947.2.25.12: SVL 33.9 mm) in preservation, from Kayin state, Myanmar: (a). dorsal view; (b). ventral view; (c). profile view of head; (d). ventral view of hand; (e). ventral view of foot.

Figure 10. Megophrys numhbumaeng sp. nov. adult male holotype (BNHS 6075: SVL 34.6 mm) in preservation, from Tamenglong district, Manipur state, India: (a). dorsal view; (b). ventral view; (c). profile view of head; (d). ventral view of hand; (e). ventral view of foot.

Figure 11. Megophrys numhbumaeng sp. nov. adult male type specimens from Tamenglong district, Manipur state, India: (a–b). holotype (BNHS 6075: SVL 34.6 mm) in life; (a). dorsolateral view; (b). ventral view; (c–d). paratype (BNHS 6076: SVL 33.8 mm) in preservation: (c). dorsal view; (d). ventral view.