Megophrys (Panophrys) hoanglienensis Tapley & Cutajar & Mahony & Nguyen & Dau & Luong & Le & Nguyen & Nguyen & Portway & Luong & Rowley 2018, sp. nov.

Megophrys (Panophrys) hoanglienensis sp. nov.

Figs. 8–13 & Table 4.

Holotype: One adult male (VNMN 2018.02), found beside a 5 m wide low-gradient shallow stream in slightly disturbed evergreen forest, Mount Fansipan, Hoang Lien National Park (HLNP), Sa Pa District, Lao Cai Province,

Vietnam (22.33518° N, 103.77947° E, 2075 m asl; Fig. 8), collected at 19:15 h on 14 June 2012 by Jodi J. L. Rowley, Dau Quang Vinh, Pham Van Sang, Tran Van Tu, Hang A Su, Hoang A Di and Dinh Van Xuan.

Paratypes: Four adult males (VNMN 0 7034, AMS R186118, AMS R186119 & AMS R186120), found in the vicinity of a 2 m wide low-gradient stream in disturbed evergreen forest, Mount Fansipan, HLNP, Sa Pa District, Lao Cai Province, Vietnam (22.32827° N, 103.78184° E, 2242 m asl; Fig. 8), collected at 19:45 h on 12 June 2012; one adult female (AMS R186121), found beside a 5 m wide low-gradient shallow stream in slightly disturbed evergreen forest, Mount Fansipan, HLNP, Sa Pa District, Lao Cai Province, Vietnam (22.33518° N, 103.77947° E, 2075 m asl), collected at 19:15 h on 14 June 2012. All aforementioned specimens collected by Jodi J. L. Rowley, Dau Quang Vinh, Pham Van Sang, Tran Van Tu, Hang A Su, Hoang A Di and Dinh Van Xuan. Two adult males (AMS R186122 & AMS R186123), found calling from a rocky overhang 1.8 m above and 1.5 m away from a 3 m wide cascading stream at the base of Love Waterfall (thác Tình Yêu) in disturbed evergreen forest on Mount Fansipan, HLNP, Tam Duong District, Lai Chau Province, Vietnam (22.35065° N, 103.77136° E, 1898 m asl; Figs. 8 & 12 A–B), collected at 22:15 h on 24 June 2016 by Jodi J. L. Rowley, Benjamin Tapley, Cong Huy Le and Nguyen Thanh Chung; three adult males (AMS R186125, AMS R186126 & AMS R186127), found beside a swampy stream in disturbed evergreen forest, Mount Ky Quan San, Bat Xat District, Lao Cai Province, Vietnam (22.30343° N, 103.37019° E, 2153 m asl), collected at 21:00 h on 0 6 September 2017 by Nguyen Thanh Chung, Luan Thanh Nguyen, Luke Harding, Timothy Cutajar, Jodi J. L. Rowley and Benjamin Tapley.

Referred specimens: One adult male (HLNP 20120624 00003), found calling from a rocky overhang 1.8 m above and 1.5 m away from a 3 m wide cascading stream at the base of Love Waterfall in disturbed evergreen forest on Mount Fansipan, HLNP, Tam Duong District, Lai Chau Province, Vietnam (22.35065° N, 103.77136° E, 1898 m asl; Figs. 8 & 12 A–B), collected at 22:15 h on 24 June 2016 by Jodi J. L. Rowley, Benjamin Tapley, Cong Huy Le and Nguyen Thanh Chung; two juvenile specimens (HLNP 20170906 0 0 0 0 4 & AMS R186124), found beside a 3 m wide stream in disturbed evergreen forest on Mount Fansipan, HLNP, Tam Duong District, Lai Chau Province, Vietnam (22.21039° N, 103.46293° E, 1882 m asl), collected at 20:00 h on 0 6 September 2017 by Nguyen Thanh Chung, Luan Thanh Nguyen, Luke Harding, Timothy Cutajar, Jodi J. L. Rowley and Benjamin Tapley; six adult males (HNUE MCC.2017.83–85, HNUE MCC.2017.88 & IEBR MCC.2017.86–87), found in the vicinity of Hang De Cha Hai stream, Che Tao Village, Che Tao Commune, Mu Cang Chai District, Mu Cang Chai Species Habitat Conservation Area, Yen Bai Province, Vietnam (21.76247° N, 104.01889° E, 2046 m asl), collected on 0 1 May 2017 by Yen Thi Do, Anh Ngoc Dao and Nam Hai Nguyen.

Etymology: Specific epithet “ hoanglienensis ” is a toponym in reference to the type locality of the species, meaning “from Hoang Lien” Range.

Suggested vernacular name: Hoang Lien horned frog (English), Ếch sừng hoàng liên (Vietnamese).

Diagnosis: Megophrys hoanglienensis sp. nov. differs from its congeners by a combination of the following morphological characters: (1) medium adult size, adult male SVL 37.4–47.6 mm (N= 11); adult female SVL 59.6 mm (N= 1); (2) small palpebral horn on upper eyelid present; (3) interdigital webbing and lateral fringes on the toes indistinct or absent; (4) snout mucronate in dorsal view; (5) TYD/EL 54.2–75.0% in adult males (N =11), 60.0% in adult female (N= 1); (6) subarticular tubercles absent; (7) palmar tubercles absent; (8) inner metatarsal tubercle present; (9) HW/SVL 37.4–42.5% in adult males (N= 11), 38.3% in adult female (N= 1); (10) SHL/SVL 44.3– 62.5% in adult males (N =11), 57.5% in adult female (N= 1); (11) tympanum clearly defined; (12) TYE/SVL 6.3– 9.5% in adult males (N= 11), 7.6% in adult female (N= 1); (13) vomerine ridges, vomerine and maxillary teeth present; (14) an advertisement call with a dominant frequency of 2.8–3.0 kHz at 18.5 °C.

Description of holotype (measurements provided in Table 4): Sexually mature male (Figs. 9 A–B, 10A–C, 11A–B). Head small, wider than long; snout mucronate in dorsal view, obtusely protruding in lateral view, rostral appendage absent; loreal region vertical and concave; canthus rostralis angular; dorsal region of the snout slightly concave; eye length 38.0% longer than the maximum tympanum diameter and subequal to the snout length; eye to tympanum distance greater than the maximum tympanum diameter; tympanum circular. Pupil in life oval, vertically orientated when dilated; nostrils orientated laterally, closer to the eyes than the snout; internarial distance subequal to the width of the eyelids, and subequal to the narrowest point between the upper eyelids; vomerine ridges present, oblique and barely separated anteriorly, with small vomerine teeth; maxillary teeth present. Tongue moderately large and feebly notched posteriorly. Forelimbs moderately long and thin; forearm length shorter than the hand length; fingers long and narrow without lateral fringes, finger length formula FI=FII=FIV<FIII; interdigital webbing absent; subarticular, supernumerary and palmar tubercles absent; thenar tubercle weak; finger tips slightly expanded relative to the adjacent digit width and flattened to oval pads; terminal grooves absent. Hindlimbs relatively long and thin; thigh length shorter than the shank length, but greater than the foot length; toes long and rounded without dermal fringes, toe tips slightly dilated relative to adjacent digit width and flattened to oval pads, terminal grooves absent; toes with rudimentary webbing; outer metatarsal tubercle, subarticular and supernumerary tubercles absent; inner metatarsal tubercle weakly defined.

F1 GURE 10. Megophrys hoanglienensis sp. nov. in preservative (holotype VNMN 2018.02). (A) Lateral view of head, (B) palmar surface of right hand, and (C) plantar surface of left foot. 5 mm scale bar.

Skin of dorsal surfaces of the body, limbs, and both dorsal and lateral surfaces of the head weakly granular; tympanum granular with borders slightly raised; very small palpebral horn present on the outer edge of the upper eyelid; supratympanic fold narrows as it passes above the tympanum, widening again before terminating above the axilla; flanks with small scattered tubercles; thin dorsolateral fold extending posteriorly from behind the supratympanic fold to the groin on each side; a weak, “V”-shaped parietoscapular ridge present, its two sides extending posteriorly from above the tympanum and meeting medially beyond the level of the axilla; a second weak inverted “U”-shaped sacral ridge present on the mid-dorsum which joins laterally with the dorsolateral folds; “V” and “U”-shaped ridges not joined at their apex, apex of ridges with black asperities; small tubercles present on the dorsal surface of the thighs, shanks and forearms. Large distinct tubercles present on the flanks, inguinal region and dorsal surface of the hindlimbs; chest and ventral surfaces of the forelimbs and shanks smooth; pectoral glands obvious, small, slightly raised, positioned level with the axilla; femoral glands small, slightly raised, one positioned equidistant from the knee and the cloaca on the posterior surface of each thigh; white skin asperities forming narrow band circummarginally on the upper and lower jaw; black asperities on the posterior parts of the upper eyelids, on the dorsum and area directly above the vent, and on tubercles of the tympanic regions, absent elsewhere.

Colour of holotype: In life (Figs. 11 A–B): Dorsally dark tan; with light tan blotches; darker brown triangular marking between the eyes with a lighter central blotch; cream supratympanic folds with black lower margin; inguinal regions light tan; dark brown hindlimbs with darker blotches; posterior surface of the thighs and shanks very dark brown; forearms light brown with a single dark bar; dorsal surface of the fingers with dark brown bars; gular, pectoral and abdomen region mottled grey-brown and cream, gular region with a medial dark brown stripe; ventral surface of thighs unmarked; pectoral glands off-yellow; iris metallic gold.

In preservative (Figs. 9 A–B & 10A–C): Markings are the same as in life, colouration differences are as follows: The majority of the dorsal and lateral surfaces of the head, body, forelimbs and hindlimbs brown; dorsolateral and supratympanic folds and flank tubercles brownish-cream; tip of the snout cream, lateral canthus rostralis dark brown; wide vertical dark brown bar below the eyes; dark brown band running from the posterior edge of the eyes, through the tympanum, and terminating where the forelimbs join the body; lower margin of the supratympanic folds dark brown, sharply contrasting with creamy grey upper margin; gular region, chest and anterior part of the abdomen primarily creamy-grey with brown speckling, and a dark brown medial bar in the gular region; dark brown blotches anterior to each of the pectoral glands, pectoral glands light cream in colour; abdomen speckled with dark brown; ventral surfaces of the thighs and shanks with diffuse pale brown mottling; ventral surfaces of the feet grey brown with cream digit tips; area surrounding the vent dark brown; forelimbs ventrally mottled with dark brown bar running longitudinally on the outer ventral surface of the forearms; grey colouration of ventral side of the hands with darker mottling and cream digit tips; femoral glands cream.

Variation: Morphometric measurements of the type series and referred specimens are provided in Table 4. Nuptial pads were not visible on one male specimen (AMS VNMN 07034) although sex was confirmed via inspection of the gonads. Two (AMS R186120 & AMS R186121) of the 12 specimens possessed rudimentary webbing between the toes. Four (VNMN 0 7034 & AMS R186118¯20) of the 12 specimens with indistinct lateral fringes on the toes. It is not clear if the presence of indistinct fringes on the toes of these specimens is an artefact of the positioning during the fixation process. Relative finger lengths are highly variable, and only one specimen (AMS R186119; FIẼFII<FIV<FIII) had the same relative finger length formula as the holotype; the remaining specimens differed from the holotype specimen in having the following relative finger lengths; FI<FIII<FIV<FII (VNMN 07034), FI<FII<FIV<FIII (AMS R186118, AMS R1 86120, AMS R186121 & AMS R186123), FII<FI<FIV<FIII (AMS R1 86122, AMS R186125 & AMS R186127), FIV<FI<FII<FIII (HLNP 2 0 120624 00003), and FIV<FI<FII<FIII (AMS R186126). Colour in life is variable from tan to dark brown (Fig. 11 A–H).

Secondary sexual characters: All sexually mature males had slightly raised nuptial pads covered with black microspinules, nuptial pads covering most of the dorsal surface of the base of FI and FII; nuptial pad oval shaped on FI and FII; the protruding fleshy projection posterior to the cloaca (a secondary sexual character of some male Megophrys, e.g., M. caudoprocta, M. koui and M. pachyproctus) is absent on all male specimens. The examined female did not possess nuptial pads.

Molecular data: Sequences generated from nine adult specimens in this study (Table 1) were most similar to “ Megophrys sp. 5” (sensu Chen et al. 2017) collected in Sa Pa District, Lao Cai Province, Vietnam; 16S rDNA sequences differed by only 0.3% uncorrected p -distance between “ Megophrys sp. 5” and our specimens (from Lao Cai & Lai Chau provinces), and by 1.1% for specimens collected approximately 58 km away in Yen Bai Province, which is greater than the intraspecific variation reported elsewhere within the subgenus Panophrys (e.g., Li et al. 2014 reported an intraspecific p -distance of 0.6% between populations of M. obesa Wang, Li & Zhao, 2014), but is lower than intraspecific variation within Megophrys sensu lato (e.g., 3.1% mean uncorrected p -distance in M. elfina; Poyarkov et al. 2017). Uncorrected p -distance was 0.8% between specimens of Megophrys hoanglienensis sp. nov. collected from Lao Cai and Lai Chau provinces. The smallest interspecific p- distance in our study was between Megophrys hoanglienensis sp. nov. and Megophrys fansipanensis sp. nov. at 3.3% where the two new species occur in syntopy supporting their position as distinct sister taxa.

Advertisement call: Call descriptions are based on the calls of one paratype (AMS R186122), five call groups and 20 calls in total were analysed. Advertisement calls were recorded at 18.5 °C ambient temperature. Calls were an average of 102.9 ms (96–108 ms) in duration (Table 5; Fig. 13). The average number of pulses per call was 18.7 (12–22). The average dominant frequency of all the analysed calls was 3.0 kHz (2.8–3.0 kHz). Calls were repeated at a rate of 2.6 calls per second for the call groups analysed, and had an average intercall interval of 274.2 ms (178– 565 ms). The number of calls within each call group ranged from 11 to 21, with an average of 17. Most call groups began at a relatively low amplitude, increasing with each call up to approximately a quarter of the duration, after which amplitude varied but did not follow a trend or pattern (Fig. 13A & B). Individual calls began with a medium relative amplitude but peaked early before declining towards the end, and the interval between the first and second pulse was longer than those between any of the following pulses (Fig. 13C).

Natural history: Megophrys hoanglienensis sp. nov. is associated with disturbed secondary broadleaf forest with a relatively open canopy. All individuals have been found at night in riparian habitat along clear water, 2–5 m wide streams with a gravel or rocky substrate. Males were calling from streamside vegetation in June 2012 and June 2016 but not during the surveys undertaken in May or September 2017. A non-gravid female was found adjacent to a wide, low-gradient, shallow stony stream in June 2016. Tadpoles were not observed at any of the locations where this species has been found (surveys undertaken in June 2012 and 2016, and in September 2015 and 2017). Megophrys hoanglienensis sp. nov. is sympatric with M. jingdongensis at 1990 m asl on Mount Fansipan, and with M. fansipanensis sp. nov. on Mount Fansipan at 2242 m asl. Megophrys hoanglienensis sp. nov. is sympatric with M. jingdongensis and M. rubrimera on Mount Ky Quan San at 2153 m asl (Tapley et al. 2018b).

Distribution and conservation status: This species is known from between 1898–2242 m asl at four localities, up to 92 km apart in the Hoang Lien Range (Sa Pa District, Lao Cai Province, HLNP; Tam Duong District, Lai Chau Province; Mount Ky Quan San, Bat Xat District, Lao Cai Province and Che Tao Commune, Yen Bai Province, Vietnam). The species’ EOO is currently predicted to be 3216 km 2 (Fig. 8). Ongoing disturbance to the species’ habitat due to forest clearance for agriculture has been observed in the parts of Sa Pa District where the species was observed. In Bat Xat District the forest in which this species occurs is being negatively impacted by fuelwood collection for the tourism industry and by the grazing of livestock. Megophrys hoanglienensis sp. nov. is likely to qualify as Endangered in accordance with the IUCN Red List of Threatened Species categories and criteria B1ab(iii).

Comparisons: Megophrys hoanglienensis sp. nov. can be distinguished from all species in the subgenus Panophrys found in mainland Southeast Asia, north of the Isthmus of Kra and neighbouring provinces of China on the basis of morphology, and from all species in the subgenus for which comparable data is available on the basis of molecular and acoustic data. Comparisons with each subgenus are discussed separately below. The following comparison is based on 11 males and one female of Megophrys hoanglienensis sp. nov.

Subgenus Brachytarsophrys: Megophrys hoanglienensis sp. nov. can be distinguished from M. carinense, M. feae and M. intermedia by the absence of a transverse fold at the base of the head (versus presence in M. carinense, M. feae and M. intermedia), and by having a smaller adult male size, SVL 41.1–47.6 mm (versus SVL> 79.1 mm; material examined).

Subgenus Ophryophryne: Megophrys hoanglienensis sp. nov. can be distinguished from all species in the subgenus Ophryophryne due to the presence (versus absence) of maxillary teeth (Poyarkov et al. 2017; material examined); further from M. elfina by having a larger adult female size, SVL 59.6 mm (versus 35.1–36.5 mm, N =6, in M. elfina; Poyarkov et al. 2017); from M. gerti by having a larger adult female size, SVL 59.6 mm (versus 43.1– 47.4 mm, N =3, in M. gerti; Poyarkov et al. 2017); from M. hansi by having a larger adult female size, SVL 59.6 mm (versus 45.1–53.9 mm, N =5, in M. hansi; Poyarkov et al. 2017; material examined); from M. koui by the absence of a protruding fleshy projection above the cloaca in sexually mature males (secondary sexual characteristic of adult M. koui; Poyarkov et al. 2017); and from M. synoria by the presence of microspinules on nuptial pads in adult males (versus microgranules on nuptial pads in adult M. synoria; Poyarkov et al. 2017; material examined).

Subgenus Xenophrys: Megophrys hoanglienensis sp. nov. differs from M. auralensis by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 60.1–76.9 mm, N = 20 in M. auralensis, N =20; Ohler et al. 2002; Neang et al. 2013); from M. damrei by having a smaller adult female body size, SVL 59.6 mm (versus 69.1 mm, N= 1, in M. damrei; Mahony 2011; material examined); from M. glandulosa by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 76.7–81.6 mm, N =10, in M. glandulosa; Fei et al. 2009; Fei et al. 1990; material examined), absence of distinct lateral fringes on toes (versus presence in M. glandulosa; Huang et al. 1998; Mahony et al. in press; material examined), and the absence of a light-coloured upper lip stripe (versus presence in M. glandulosa; Fei et al. 1990; material examined); from M. lekaguli by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 55.6–68.1 mm, N =8, in M. lekaguli; Stuart et al. 2006b; material examined); from M. major by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 72.4–79.4 mm; N= 5, in M. major; material examined), a lack of lateral fringes on the toes (versus presence in M. major; Boulenger 1908; Mahony et al. in press; material examined), a lack of distinct toe webbing (versus at least one quarter webbed in M. major; Boulenger 1908; material examined), and the absence of a light-coloured upper lip stripe (versus presence in M. major; Boulenger 1908; Mahony et al. in press; material examined); from M. maosonensis by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 58.0–76.0 mm, N =6, in M. maosonensis; Bourret 1937), a lack of distinct interdigital toe webbing (versus toes up to one quarter webbed in M. maosonensis; Bourret 1937), and the absence of a lightcoloured upper lip stripe (versus presence in M. maosonensis; Bourret 1937); from M. pachyproctus by having a larger tympanum to eye ratio, TYD/EL 54.2–75.0% (versus 29.0%, N =3, in M. pachyproctus; Huang et al. 1981), and the absence of a protruding projection above the cloaca in male specimens (versus presence in M. pachyproctus; Huang et al. 1981); from M. parva by having a larger adult size, male SVL 37.4–47.6 mm, (versus male SVL 33.9–36.0 mm, N =2, material examined) and female SVL 59.6 mm (versus female SVL 41.1–41.4 mm, N =2, in M. parva; material examined), a typically larger tympanum to eye ratio, TYD/EL 54.2–75.0% (versus 40.0¯55.0%, N =4, in M. parva; material examined); and from M. takensis by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 57.3–53.0 mm, N =3, in M. takensis; Mahony 2011; material examined).

Subgenus Panophrys: Megophrys hoanglienensis sp. nov. differs from M. binchuanensis by having a larger adult male body size, SVL 37.4–47.6 mm (versus 32.0–36.0 mm, N =4, in M. binchuanensis; Ye & Fei 1995), the absence of subarticular tubercles (versus presence in M. binchuanensis; Ye & Fei 1995) and the absence of lateral fringes on the toes (versus presence in M. binchuanensis; Ye & Fei 1995); from M. boettgeri by having a larger female body size, SVL 59.6 mm (versus 35.3–46.5 mm, N= 3, in M. boettgeri; material examined), and the presence of vomerine ridges and vomerine teeth (versus absence in M. boettgeri; Boulenger 1899; material examined); from M. brachykolos by subarticular tubercles on fingers absent (versus present on the base of all fingers in M. brachykolos; Inger & Romer 1961; material examined), and the presence of vomerine ridges and vomerine teeth (versus absence in M. brachykolos; Inger & Romer 1961; material examined); from M. daweimontis by having a larger adult body size, male SVL 37.4–47.6 mm, female SVL 59.6 mm (versus male SVL 34.0–37.0 mm, N =17, female SVL 40.0–46.0 mm, N =3, in M. daweimontis; Rao & Yang 1997), and the absence of palmar tubercles (versus distinct and red in life in M. daweimontis; Rao & Yang 1997); from Megophrys fansipanensis sp. nov. by larger female body size, SVL 59.6 mm (versus 41.7–42.5 mm, N =2, in Megophrys fansipanensis sp. nov.; this study), larger male TYE/SVL ratio, 6.3–9.5% (versus 4.0–6.0%, N =15, in M. fansipanensis sp. nov.; this study), and advertisement call (see Bioacoustics comparison); from M. jingdongensis by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 53.0– 56.5 mm in M. jingdongensis; Fei et al. 2012; Li et al. 2014), and a lack of distinct interdigital toe webbing (versus at least one quarter webbed in M. jingdongensis; Fei & Ye 1983); from M. latidactyla by the absence of lateral fringe on the toes (versus wide dermal fringes in M. latidactyla; Orlov et al. 2015), and the absence of distinct interdigital webbing (versus at least one quarter webbed in M. latidactyla; Orlov et al. 2015); from M. minor by the presence of vomerine teeth (versus absence in M. minor; Stejneger 1926), and male advertisement call (see Bioacoustics section); from M. omeimontis by having a smaller adult male body size, SVL 37.4–47.6 mm (versus 51.6–60.9 mm, N= 5, in M. omeimontis; material examined), and a lack of lateral fringes on toes (versus presence in M. omeimontis; Liu, 1950; material examined); from M. palpebralespinosa by a lack of distinct interdigital webbing between the toes (versus approximately half webbed in M. palpebralespinosa; Bourret 1937), and a lack of lateral fringes on the toes (versus presence in M. palpebralespinosa; Bourret 1937); from M. rubrimera by having a larger adult male body size, SVL 37.4–47.6 mm (versus 26.7–30.5 mm, N= 8, in M. rubrimera; Tapley et al. 2017a; material examined), a larger adult female body size SVL 59.6 mm (versus 26.6–30.8 mm, N =4, in M. rubrimera; Tapley et al. 2018b; material examined), absence of lateral fringes on toes (versus presence in M. rubrimera, Tapley et al. 2017a; material examined), the absence of a red-orange groin, inner thigh and outer surface of shank (versus presence in M. rubrimera; Tapley et al. 2017a), and advertisement call (see Bioacoustics comparison); from M. spinata by the lack of interdigital webbing between toes (versus distinctly webbed in M. spinata; Hu et al. 1973), and the absence of large keratinised spines on nuptial pads of adult males (versus presence of keratinised spines in adult male M. spinata; Hu et al. 1973); and from M. wuliangshanensis by having a larger adult male body size, SVL 37.4–47.6 mm (versus 27.3–31.6 mm, N =10, in M. wuliangshanensis; Ye & Fei 1995), a larger tympanum on males, mean male TYD/EL 62.9% (versus mean male TYD/EL 48.8%, N =10, in M. wuliangshanensis; Ye & Fei 1995), and the presence of vomerine teeth (versus absence in M. wuliangshanensis; Fei et al. 2009, 2012).

From species not yet assigned to a subgenus: Megophrys hoanglienensis sp. nov. differs from M. feii by having a larger adult male body size, SVL 37.4–47.6 mm (versus 24.3–25.1 mm, N =4, in M. feii; Yang et al. 2018), the presence of vomerine ridges and vomerine teeth (versus absence in M. feii; Yang et al. 2018), the absence of lateral fringes on toes (versus presence in M. feii; Yang et al. 2018), the presence of nuptial pads on the fingers of breeding males (versus absence in M. feii; Yang et al. 2018), and the absence of a protruding projection posterior to cloaca (versus presence in both sexes of M. feii; Yang et al. 2018)

Bioacoustic comparison: The male advertisement call of Megophrys hoanglienensis sp. nov. recorded at 18.5 °C differs from those of its four congeners (subgenus Panophrys) found in mainland Southeast Asia, north of the Isthmus of Kra and neighbouring provinces of China for which calls have been described. The male advertisement call of Megophrys hoanglienensis sp. nov. differs from M. boettgeri (data from Wang et al. 2014, recorded at 15.0– 18.0 °C) by having an average call duration of 102 (96–108) ms, N =20 (versus average 54 ms, N =76, in M. boettgeri), and lacking clear harmonics (versus relatively clear harmonics at approximately 5.0 kHz in M. boettgeri); from Megophrys fansipanensis sp. nov. (recorded at 15.3–18.3 °C; this study) by having an average call duration of 102 (96–108) ms, N =20 (versus 41.9 [34–49] ms, N= 60, in Megophrys fansipanensis sp. nov.), an average dominant frequency of 3.0 (2.8–3.0) kHz, N =20 (versus average 3.8 [3.6–4.7] kHz, N= 60, in Megophrys fansipanensis sp. nov.), and an average of 18.7 (12–22) pulses per call, N =20 (versus 11.6 [10–14] pulses per call, N =60, in Megophrys fansipanensis sp. nov.); from M. minor (data from Jiang et al. 2001, recorded at 14.0 °C) by having the following call parameters, a dominant frequency of 2.8–3.0 kHz, N =20 (versus 3.4–3.5 kHz, N= 13, in M. minor), a call repetition rate of 2.6 calls/s, N =20 (versus average 4.0 calls/s, N =14, in M. minor), and lacking clear harmonics (versus relatively clear harmonics at approximately 7.2 kHz in M. minor); from M. rubrimera (data from Tapley et al. 2017a, recorded at 21.0–22.9 °C) by having an average dominant frequency of 3.0 (2.8–3.0) kHz, N =20 (versus average 3.3 [3.2–3.4] kHz, N =60, in M. rubrimera), an average call duration of 102 (96–108) ms, N =20 (versus average 73.3 [62–85] ms, N= 60, in M. rubrimera), and a call repetition rate of 2.6 calls/s (versus an average of 3.3 [3.1–3.4] calls/s, N =60, in M. rubrimera).