Microhyla tetrix, Poyarkov & Pawangkhanant & Gorin & Juthong & Suwannapoom, 2020

Poyarkov, Nikolay A., Pawangkhanant, Parinya, Gorin, Vladislav A., Juthong, Watinee & Suwannapoom, Chatmongkon, 2020, A new species of miniaturised narrow-mouth frog of the genus Microhyla Tschudi, 1838 (Amphibia: Anura: Microhylidae) from northern Tenasserim, Thailand, Journal of Natural History 54 (23 - 24), pp. 1525-1558 : 1535-1549

publication ID	https://doi.org/ 10.1080/00222933.2020.1804005
publication LSID	lsid:zoobank.org:pub:BDEAEAE3-D7C3-463C-B184-4F23C09252FA
persistent identifier	https://treatment.plazi.org/id/FAB213BA-FEFF-418B-B656-950D475FA202
taxon LSID	lsid:zoobank.org:act:FAB213BA-FEFF-418B-B656-950D475FA202
treatment provided by	Carolina
scientific name	Microhyla tetrix
status	sp. nov.

Treatment

Microhyla tetrix sp. nov.

( Figures 3–7 View Figure 3 View Figure 4 View Figure 5 View Figure 6 View Figure 7 ; Table 1)

http://www.zoobank.org/ urn:lsid:zoobank.org:act:FAB213BA-FEFF-418B-B656-950D475FA202

Chresonymy

Microhyla annectens View in CoL – Smith 1916: 169 (1 specimen, coll. by the author from ‘ Klong Bang Lai , Patiyu’, now in Pathio District, Chumphon Province, Thailand) .

Microhyla annectens View in CoL – Taylor 1962: 540–541.

Microhyla sp. – Taksintum et al. 2009: 22–29 (Kui Buri NP, Prachuap Khiri Khan Province, Thailand).

Microhyla annectens View in CoL – Taksintum et al. 2010: 104, 105, 108, 121 (Kui Buri NP, Prachuap Khiri Khan Province, Thailand).

Microhyla sp. 2 – Gorin et al. 2020 (specimens from Surat Thani and Phetchaburi provinces, Thailand).

Holotype. AUP 00603, an adult female from a lowland dipterocarp tropical forest in Klong Sok District , Surat Thani Province, Thailand [coordinates 8.86578°N, 98.60793°E; elevation 80 m above sea level (asl)], collected on 27 May 2018 at 22:00 h by P. Pawangkhanant and C. Suwannapoom. GoogleMaps

Paratypes. Twelve specimens, including AUP 00605, AUP 00604 and AUP 00606, three adult males from the same locality and with the same collection information as the holotype; ZMMU A7261 View Materials (field number NAP-08215), an adult male from a lowland secondary dipterocarp tropical forest in Klong Sok District , Surat Thani Province, Thailand (coordinates 8.86578°N, 98.60793°E; elevation 80 m asl), collected on 7 June 2018 at 20:00 h by P GoogleMaps . Pawangkhanant and N.A. Poyarkov; AUP 00601, AUP 00602, AUP 00600 and ZMMU A7260 View Materials (field number NAP-07479), four adult females from the same locality and with the same collection information as the holotype; ZMMU A6034 View Materials (field number NAP-06654), an adult male, and ZMMU A6033 View Materials (field number NAP-06653), an adult female from a lowland secondary dipterocarp tropical forest in Phanom District , Surat Thani Province, Thailand (coordinates 8.90778°N, 98.53306°E; elevation 70 m asl), collected on 27 May 2018 at 19:00 h by P GoogleMaps . Pawangkhanant, C. Suwannapoom and N.A. Poyarkov; ZMMU A6032 View Materials (field number NAP-06654), an adult male from lowland dipterocarp forest in Khao Sok District , Surat Thani Province, Thailand (coordinates 8.86907°N, 98.60914°E; elevation 70 m asl), collected on 28 May 2018 at 20:00 h by N GoogleMaps .A. Poyarkov, P. Pawangkhanant, and C. Suwannapoom; and ZMMU A6035 View Materials (field number NAP-08216), an adult male from secondary lowland forest in Khao Kra Puk forest , Phetchaburi Province, Thailand (coordinates 12.67597°N, 99.68404°E; elevation 300 m asl), collected on 28 June 2017 at 20:00 h by P GoogleMaps . Pawangkhanant.

Referred specimens. AUP-00559 and AUP-00560, two adult males collected from the environs of Wat Tham Sanook , Banna Subdistrict, Mueng District, Chumphon Province, Thailand (coordinates 10.48001°N, 99.07497°E; elevation 620 m asl), on 16 August 2018, by P GoogleMaps . Pawangkhanant and C . Suwannapoom . An adult male specimen from Ao Nang area, Krabi Province, Thailand (coordinates 8.02922°N, 98.83476°E; elevation 210 m asl), recorded by P GoogleMaps . Pawangkhanant and P . V. Yushchenko (specimen released; see Figure 5 View Figure 5 (a)) .

Diagnosis. The new species is allocated to the genus Microhyla Tschudi, 1838 based on the following combination of characters diagnostic for this genus ( Parker 1934; Inger 1989; Poyarkov et al. 2014, 2019): small body size; comparatively narrow head; eyes small with circular pupil; lack of small spine-like projection of skin at heel and elbow; maxillary and vomerine teeth absent; snout less than twice diameter of eye; tongue obovate, entire and free posteriorly; fingers without webbing; toes with basal webbing; palmar tubercles distinct; prominent inner and outer metatarsal tubercles on foot; supratympanic fold present; tympanum hidden under skin.

Microhyla tetrix sp. nov. is diagnosed by a combination of the following morphological attributes: small body size with significant body size dimorphism (male SVL 10.1–13.7 mm in seven individuals; female SVL 15.2–17.6 mm in six individuals); body habitus slender; head large, notably shorter than wide, snout ovate in dorsal and bluntly rounded in lateral views, slightly protruding above lower jaw; canthus rostralis rounded, distinct; loreal region concave; nares with lateral orientation; skin on dorsum feebly granular, ventral surfaces smooth; a characteristic V-shaped glandular wart in scapular area; a dorsolateral row of glandular tubercles; mid-vertebral skin ridge and dorsomedial stripe absent; supratympanic fold indistinct; finger I well developed, equal in length to half of finger II length; II–IV fingers bearing discs with terminal grooves; in males finger III massive with its base much wider than finger disc; all toes bearing large discs with dorso-terminal grooves, discs on toes III–IV with short median longitudinal notches; two indistinct palmar tubercles (inner palmar tubercle ovoid, outer palmar tubercle almost rounded); two metatarsal tubercles (inner elongated, prominent; outer rounded, protruding); hind limbs long, tibiotarsal articulation of adpressed limb reaching far beyond the snout; rudimentary web between fingers II–III; toe webbing well-developed, reaching discs at all toes except toe III; webbing formula: I 1–2 II 1–2 III 1–2½ IV 2½–1 V; eyelids dorsally with few tiny granules, enlarged superciliary tubercles or projections absent; dorsum brownish-grey typically with a darker hourglass- or ‘teddy-bear’-shaped brown marking; dorsolateral line ventrally underlined with a series of black elongated blotches; light streak from eye to axilla dorsally edged with brown or black line; posterior surfaces of thighs and cloacal region with few brown stripes; chin with grey mottling, chest and belly immaculate.

Interspecific genetic p-distances in 16S rRNA gene fragment between the new species and its congeners vary from 7.1% to 15.8%.

Description of holotype ( Figures 3–4 View Figure 3 View Figure 4 ). Small-sized female specimen in a good state of preservation, with SVL 17.6 mm; habitus slender ( Figures 3 View Figure 3 (a), 4), head comparatively large, notably shorter than wide (HL/HW 84.4%); snout ovate in dorsal view ( Figure 3 View Figure 3 (a)), bluntly rounded in profile ( Figure 3 View Figure 3 (c)), slightly protruding above lower jaw ( Figure 3 View Figure 3 (b,c)), subequal to eye diameter (EL/SL 105.4%); eye rounded, comparatively small, slightly protuberant in lateral view ( Figure 3 View Figure 3 (c)), not protuberant in dorsal view ( Figure 3 View Figure 3 (a)),

(Continued) pupil circular ( Figure 3 View Figure 3 (c)); dorsal surface of head slightly convex, canthus rostralis rounded, distinct; loreal region slightly concave; nostrils rounded, placed more towards the lateral sides of snout, located closer to tip of snout than to eye ( Figure 3 View Figure 3 (c)); tympanum hidden under skin of temporal region; supratympanic fold indistinct; maxillary and vomerine teeth absent; vocal sac single, subgular; tongue obovate, entire and free at the base, lacking papillae.

Fore limbs short, ca. one-third of hind limb length (FLL/HLL 34.3%); hand short, comprising 60.1% of lower arm length (HAL/LAL) and 40.1% of fore limb length (HAL/ FLL); fingers comparatively thin, rounded in cross-section, first finger length almost equal to half of second finger length (1FL/2FL 51.6%); relative length of fingers: I <IV <II <III (see Figure 3 View Figure 3 (d)). Finger webbing absent between all fingers except II and III where remnants of rudimentary basal web can be observed; dermal fringes absent; tips of all fingers rounded, tip of finger I not enlarged, tips of fingers II–IV notably widened forming discs, lacking median longitudinal grooves, but showing dorso-terminal grooves; third finger disc the largest; subarticular tubercles on volar surface of fingers barely distinct, flattened; finger subarticular tubercle formula: 1:1:2:2; nuptial pad absent; two metacarpal (palmar) tubercles: inner palmar tubercle rounded with indistinct borders; outer palmar tubercle indistinct with its borders almost indiscernable, ovoid-shaped, slightly longer than inner (IPTL/OPTL 85.7%); inner and outer palmar tubercles separated by a flat surface lacking medial or supernumerary palmar tubercles.

Hind limbs comparatively long, tibia length much longer than half of snout–vent length (TL/SVL 68.2%), hind limb length over 1.5 times longer than snout–vent length (HLL/SVL 188.4%); tibiotarsal articulation of adpressed limb reaching well beyond snout (checked prior to preservation); tibia slightly longer than foot (FL/TL 91.0%); relative toe lengths: I <II <V <III <IV; tarsal fold on inner surface of tarsus absent; tips of all toes rounded and widened, forming broad terminal discs ( Figure 3 View Figure 3 (e)); all toe discs having dorso-terminal groves; the discs on toes III and IV the largest, distally having tiny median dorso-longitudinal notches not reaching one-third of disc length; toes long, thin, slightly flattened in cross-section; toe webbing well developed between all toes, reaching discs at all toes except toe IV, webbing formula: I 1–2 II 1–2 III 1–2½ IV 2½–1 V; toe subarticular tubercles distinct, rounded, slightly protruding; toe subarticular tubercle formula: 1:1:2:3:2; two metatarsal tubercles: inner metatarsal tubercle elongated, oval, slightly prominent; outer metatarsal tubercle small, rounded, slightly shorter than inner (OMTL/ IMTL 83.8%), protruding ( Figure 3 View Figure 3 (e)).

Skin on dorsum feebly granular with numerous small flat granules evenly scattered on dorsal surfaces of body, becoming smaller on dorsal surfaces of head and limbs ( Figure 4 View Figure 4 ); a distinct elevated V-shaped glandulous wart comprised of a series of elongated tubercles in scapular area; several large glandular tubercles form a row in supratympanic area running from the posterior eye corner dorsolaterally and disappearing at groin; upper eyelids covered with a few tiny tubercles along the outer edge of eyelids; large superciliary tubercles or projections absent; mid-vertebral dermal ridge absent ( Figure 3 View Figure 3 (a)); skin on dorsolateral surfaces shagreened; dorsal sides of limbs covered with numerous small flattened tubercles, ventral surfaces of trunk, head and limbs smooth.

Colouration of holotype in life. Dorsal surfaces of head and body with brownish-grey background colouration ( Figure 3 View Figure 3 (a)); dorsal surface of snout light brown; a distinctly darker

brown hourglass-shaped figure starts at the interorbital bar between the eyelids, running posteriorly to scapular region with its narrowest part at head basis; thick light beige lines running from posterior eye corners edging the hourglass-shaped dark marking forming a) (-shaped light figure, which continues farther posteriorly to groin (the light brown line interrupts on the left side of the body) ( Figure 3 View Figure 3 (a)); a pair of round light beige spots on dorsal surface in sacral area; an azygous light brown blotch above the cloaca ( Figure 3 View Figure 3 (a)). Dorsolateral lines ventrally edged with thick black irregular elongated blotches; body flanks light purplish-grey with numerous tiny white speckles ( Figure 4 View Figure 4 ); eyelids dark brown; lateral sides of head grey with brownish mottling; a light yellow streak running from the posterior edge of eye to mouth corner, dorsally edged with a thick black line ( Figure 4 View Figure 4 ). Dorsal surfaces of fore limbs pinkish-brown with tiny reddish spots; two narrow dark brown bars on dorsal surface of each forearm closer to its distal end ( Figure 3 View Figure 3 (a)). Dorsal surfaces of thighs and shanks brownish-grey with two thin dark brown lines alternating on each hind limb, forming a continuous pattern when the leg is folded; each knee dorsally with large irregular brown spot; cloacal area with a large black blotch dorsally edged with beige and with a small lighter brown streak medially ( Figure 3 View Figure 3 (a)). Fingers and toes dorsally grey to light brown; a few brown blotches at tibiotarsus. Throat with very thin grey mottling becoming denser towards the jaws, chest and venter immaculate, light nacreous-grey to whitish ( Figure 3 View Figure 3 (b)); ventral surfaces of limbs pinkish-grey; hands and feet ventrally with tiny brownish mottling. Pupil black, circular, edged with narrow copper line, dense copper reticulations throughout iris; sclera dark ( Figure 3 View Figure 3 (c)).

Colouration of holotype in preservative. After preservation in ethanol for over 2 years, colouration faded significantly and turned dark grey, ventral surfaces changed to light grey. Light markings on dorsum and dark stripes on limbs are still distinct, and generally the colouration pattern remained unchanged.

Measurements of holotype (in mm). SVL 17.6; HL 5.1; SL 2.1; EL 2.2; N-EL 1.0; HW 6.1; IND 1.4; IOD 1.8; UEW 1.3; FLL 11.4; LAL 7.8; HAL 4.7; IPTL 0.5; OPTL 0.6; HLL 33.1; TL 12.0; FL 10.9; IMTL 0.7; OMTL 0.6; 1FL 1.0; 2FL 1.9; 3FL 2.8; 4FL 1.2; 1TOEL 1.9; 2TOEL 3.0; 3TOEL 5.1; 4TOEL 6.1; 5TOEL 3.5; 1FDD 0.4; 2FDD 0.5; 3FDD 0.7; 4FDD 0.5; 1TDD 0.6; 2TDD 0.9; 3TDD 1.0; 4TDD 1.0; 5TDD 0.8.

Variation. Morphometric variation of the type series is presented in Table 1. Female paratypes generally agree well with the holotype. Males of the new species (adult male SVL 10.1–13.7 mm, mean 12.4 ± 1.16 mm; N = 7) are significantly smaller than females, and their values do not overlap (adult female SVL 15.2–17.6 mm, mean 16.3 ± 0.94 mm; N = 6) ( Table 1). In addition to much smaller body size, males of the new species also differ significantly from females in fore limb morphology: males have relatively longer fore limbs than females (p <0.05), with notably thicker arms; they also have smaller discs on fingers (mean 3FDD = 0.4 ± 0.03 mm in males vs 0.6 ± 0.04 mm in females), and the hand is more elongated with rudimentary fourth finger, while the third finger is massive and broadened, and is much wider at its base than the finger disc (see Figures 6 View Figure 6 (a), 7(c–d)). This gives the hand in males a fin-like appearance; similar hand morphology was not reported in other Microhyla species. The thickness of the third finger in comparison to other fingers, and the degree of development of the fourth finger, vary among the male specimens examined (see Figures 6 View Figure 6 (a), 7(c–d)).

Colouration of the type series also varies significantly. Female paratype AUP 00601 has a similar dorsal colour and pattern to the holotype, but slightly differs from it in the arrangement of light dorsolateral markings ( Figure 5 View Figure 5 (b)) . All types showed blackish spots on V-shaped warts in scapular region and a black spot in the cloacal area ( Figures 5 View Figure 5 , 7 View Figure 7 ); the shape of the medial light streak on the latter varied ( Figure 7 View Figure 7 ). Female paratype ZMMU A6033 View Materials has much lighter reddish-brown dorsal colouration than the holotype, and the dark line above the light eye-axilla streak is very short and is located near the eye corner ( Figure 5 View Figure 5 (e)); similar lighter colouration was also recorded in a female from Chumphon Province, where the dark line was almost indiscernible ( Figure 5 View Figure 5 (d)) . Male paratype ZMMU A6035 View Materials from Phetchaburi Province showed a thick dark line above the white eye-axilla streak and a contrasting dorsal colouration with a clear dark brown ‘teddy-bear’-shaped dorsal marking (sensu Rakotoarison et al. 2017) edged with light beige ( Figures 5 View Figure 5 (f), 7(d)), the same as the male paratype AUP 00605 from Surat Thani Province ( Figure 5 View Figure 5 (c)) . Generally, the dorsal pattern in females ( Figure 7 View Figure 7 (a–b)) was less bright and less contrasting than in males ( Figure 7 View Figure 7 (c–d)). Female paratype AUP 00600 showed an almost uniform reddish-brown colouration of the dorsum with contrasting black spots in the scapular region ( Figure 7 View Figure 7 (b)) .

Natural history. Microhyla tetrix sp. nov. inhabits diverse forest habitats from primary and secondary disturbed lowland tropical forests to montane evergreen forests of Tenasserim range, where it was recorded at elevations of 50–800 m asl. The primary lowland tropical forest at the type locality (at Klong Sok Disrict, Surat Thani Province, Thailand) was dominated by trees of the families Dipterocarpaceae ( Anisoptera costata Korth. , Hopea odorata Roxb. , Dipterocarpus gracilis Blume and Parashorea stellata Kurz ), Dilleniaceae ( Dillenia indica L., D. pentagyna Roxb. ), Moraceae ( Artocarpus chama Buch. - Ham., A. lacucha Buch. -Ham.) and Araliaceae ( Trevesia palmata (Roxb. ex Lindl.) Vis. ) ( Figure 8 View Figure 8 (a)).

Microhyla tetrix sp. nov. is a very secretive frog; all type specimens were collected at night from 19:00 to 23:00 h after heavy rains, and were mostly recorded while sitting on plant stems, leaves or rotten logs, or hiding in the leaf litter. We recorded calling males in April and May near temporary pools in the forest. Calling males hide under dead leaves, in small holes in the dirt on the banks, or keep to the water surface, often forming large aggregations at the spawning site ( Figure 8 View Figure 8 (d)). Diet and predators of the new species are unknown. Egg size is unknown; eggs bicoloured, with a dark brown animal pole embedded in a gluey, transparent jelly layer; clutch size and morphology are not known. The tadpole of Microhyla tetrix sp. nov. was briefly described and illustrated by Taksintum et al. (2009); it appears that larval development time is very short and the tadpoles are largely endotrophic.

In primary lowland tropical forests at the type locality, Microhyla tetrix sp. nov. was found in sympatry with Microhyla heymonsi , M. mantheyi , Kaloula latidisca Chan, Grismer and Brown , Micryletta cf. lineata Taylor and Kalophrynus cf. kiewi Matsui, Eto, Belabut and Nishikawa ( Microhylidae ); Humerana miopus (Boulenger) , and Sylvirana malayana Sheridan and Stuart (Ranidae) ; Polypedates discantus Rujirawan, Stuart and Aowphol , and Rhacophorus nigropalmatus Boulenger (Rhacophoridae) . In the environs of Wat Tham Sanook (Chumphon Province), the new species was recorded in lowland karst secondary forest close to rubber and oil palm plantations in a highly disturbed habitat, in sympatry with the following anuran species: Microhyla butleri (Microhylidae) , Duttaphrynus melanostictus (Schneider) and Ingerophrynus parvus (Boulenger) (Bufonidae) .

Distribution. Microhyla tetrix sp. nov. is currently known from nine localities in western and south-western Thailand, and is distributed from Ratchaburi Province (Suan Phueng District; see locality 1 in Figure 1 View Figure 1 ) in the north to Krabi Province in the south (see locality 9, Figure 1 View Figure 1 ). The range of Microhyla tetrix sp. nov. covers the northern part of the Thai–Malay Peninsula (northern Tenasserim); the major part of its distribution lies to the north of the Isthmus of Kra, although the southernmost population in Krabi Province (locality 9, Figure 1 View Figure 1 ) is located south of this important biogeographic border.

The new species was recorded from low elevations ca. 50–800 m asl. The actual extent of the distribution of Microhyla tetrix sp. nov. is unknown. Since at least three populations are found within less than 10 km of the Thai– Myanmar international border, the new species is likely to be found in the southern part of Tanintharyi Division of Myanmar (Burmese Tenasserim), although a number of recent herpetofaunal surveys did not reveal the presence of Microhyla tetrix sp. nov. in this area ( Mulcahy et al. 2018). The historical record of ‘ Microhyla annectens ’ from ‘Klong Bang Lai, Patiyu’ (now in Pathio District, Chumphon Province) by Smith (1916) (see locality 4, Figure 1 View Figure 1 ) lies between the confirmed records of the new species from Chumphon and Pruchuap Khiri Khan provinces; the morphological description of ‘ Microhyla annectens ’ by Smith (1916) also fits the diagnosis of Microhyla tetrix sp. nov.

Conservation status. At present, the new species is known from six provinces of Peninsular Thailand; its occurrence in Phang Nga and Ranong provinces, as well as in the adjacent areas of Tanintharyi Division of southern Myanmar, is anticipated. The species has been rarely recorded to date, possibly due to its secretive biology; the population trend of the new species is currently unknown. The new species occurs in several national parks of south-western Thailand, including Kaeng Krachan NP and Kui Buri NP, and likely also in Khao Sok NP and Khlong Phanom NP; it may also inhabit a number of other conservation areas in southern Peninsular Thailand. Hence, we suggest Microhyla tetrix sp. nov. be considered a species of Least Concern (LC) following the International Union for Conservation of Nature’s Red List categories ( IUCN Standards and Petitions Subcommittee 2017).

Etymology. The specific name ‘ tetrix ’ is a Latin noun given in apposition derived from the Ancient Greek word ‘ tettix ’ (ΤΕΤΤιξ), meaning a grasshopper or cicada. The name is given in reference to the advertisement call of the new species, remarkably resembling a call of orthopterans, especially that of ground-hoppers of the family Tetrigidae . The recommended common name in English is ‘Tenasserim narrow-mouth frog’. The recommended common name in Thai is ‘ Eung Jiew Tenasserim ’ (อึ่งจิ๋วตะนาวศรี).

Comparisons. In having toes with well-developed webbing, reaching discs at all toes except toe III (I 1–2 II 1–2 III 1–2½ IV 2½–1 V), Microhyla tetrix sp. nov. can be easily distinguished from all those congeners which have basal or rudimentary webbing on toes: M. achatina , M. arboricola , M. beilunensis , M. borneensis , M. chakrapanii , M. fanjingshanensis , M. fissipes , M. fodiens , M. fusca Andersson, 1942 , M. gadjahmadai , M. heymonsi , M. irrawaddy , M. kodial , M. laterite , M. maculifera Inger, 1989 , M. mihintalei , M. minuta , M. mixtura , M. mukhlesuri , M. mymensinghensis , M. nilphamariensis , M. okinavensis , M. orientalis , M. ornata , M. picta , M. pineticola , M. rubra and M. taraiensis . Furthermore, Microhyla tetrix sp. nov. has a slender body habitus and can be easily distinguished from those species of Microhyla which have stout body habitus and an enlarged spade- or shovelshaped outer metatarsal tubercle as an adaptation to digging: M. rubra , M. mihintalei , M. taraiensis , M. picta and M. fodiens .

The new species has a diminutive body size, with adult SVL 10.1–13.7 mm in males and 15.2–17.6 mm in females; these values are among the smallest known for the genus Microhyla (see Gorin et al. 2020). A number of Microhyla species can be distinguished from Microhyla tetrix sp. nov. by notably greater and not overlapping values of SVL in both sexes: M. annamensis (male SVL 15.2–19.8 mm; female SVL 18.2–22.6 mm), M. annectens (male SVL 14.4–15.6 mm; female SVL 18.2–18.4 mm), M. aurantiventris (male SVL 25.2–27.0 mm; female SVL 30.5 mm), M. berdmorei (male SVL 23.8–28.9 mm; female SVL 26.2–45.6 mm; including M. fowleri Taylor, 1934 , considered a junior synonym of M. berdmorei by Matsui et al. 2011), M. butleri (male SVL 20.0–25.0 mm; female SVL 21.0– 26.0 mm), M. darevskii Poyarkov, Vassilieva, Orlov, Galoyan, Tran, Le, Kretova and Geissler, 2014 (male SVL 27.0– 32.6 mm), M. darreli (male SVL 15.1–15.7 mm), M. eos (male SVL 21.5 mm; female SVL 26.9–27.8 mm), M. fusca (male SVL 23 mm), M. karunaratnei (male SVL 15.8–19.1 mm; female SVL 19.6–21.0 mm), M. malang (male SVL 18.7–22.2 mm; female SVL 19.0– 23.4 mm), M. mantheyi (male SVL 15.0– 29.2 mm; female SVL 14.8–24.1 mm), M. marmorata (male SVL 18.8–21.5 mm; female SVL 21.1– 23.2 mm; including M. pulverata Bain and Nguyen, 2004 considered a junior synonym of M. marmorata by Gorin et al. 2020), M. palmipes (male SVL 16 mm; female SVL 21.8 mm), M. pulchella (male SVL 14.7–21.6 mm; female SVL 18.1–25.8 mm) and M. pulchra (male SVL 23.0–32.0 mm; female SVL 28.0– 36.5 mm).

Further, Microhyla tetrix sp. nov. has a well-developed first finger equal in length to one-half of the second finger, while in a number of its congeners the first finger is reduced or is shorter than one-half of the second finger length: M. borneensis , M. nanapollexa , M. palmipes , M. perparva , M. petrigena (first finger reduced to a nub or bulge), M. achatina , M. annamensis , M. annectens , M. arboricola , M. beilunensis , M. berdmorei , M. fanjingshanensis , M. fissipes , M. fodiens , M. fusca , M. malang , M. mantheyi , M. marmorata , M. mihintalei , M. mixtura , M. orientalis , M. picta , M. pineticola , M. pulchella , M. pulchra and M. pulverata (smaller than 1/2 of second finger length).

The new species was previously confused with M. annectens ( Smith 1916; Taksintum et al. 2010) but it can be distinguished from this species and other members of the M. annectens species group in having two metatarsal tubercles (vs a single metatarsal tubercle in M. annectens , M. arboricola , M. maculifera , M. nanapollexa , M. perparva , M. petrigena and M. pulchella ).

Since Microhyla tetrix sp. nov. belongs to the M. superciliaris species group of Gorin et al. (2020), comparisons with species within this clade appear to be the most pertinent. The new species can be distinguished from Sri Lankan and south Indian members of the M. superciliaris group, namely M. darreli , M. karunaratnei , M. laterite , M. sholigari and M. zeylanica (members of the M. zeylanica group of Garg et al. 2019), by having nostrils placed towards the lateral side of the snout (vs placed dorsally); and finger and toe tips with well-developed discs bearing dorso-terminal grooves (vs small finger discs without grooves, and small toe discs with circum-marginal grooves in M. zeylanica or dorsoterminal grooves with dorsal surfaces of toe discs bifurcating distally in all other species).

The new species can be further distinguished from M. eos inhabiting Northeast India in dorsal colouration (brown hourglass- or ‘teddy-bear’-shaped pattern vs characteristic inverted V-shaped or ‘teddy-bear’-shaped figure edged with white with numerous light brown lines forming contrasting agate-like pattern in M. eos ), smaller body size (see above), much better developed toe webbing reaching toe discs at all toes except toe III (webbing formula I 1–2 II 1–2 III 1–2½ IV 2½–1 V vs I 1½–2 II 1 2/3–3 III 2½–4 IV 4––1½ V in M. eos ), less developed discs on fingers, present on fingers II–IV (vs wider discs on all four fingers in M. eos ), in having granular skin on dorsum (vs smooth to shagreened dorsal skin in M. eos ), and by longer hind limbs with tibiotarsal articulation reaching far beyond snout when leg is adpressed to body (vs to snout in M. eos ).

Microhyla tetrix sp. nov. superficially resembles its sister species M. superciliaris Parker in body size and general morphology, but can be distinguished by the following suite of morphological characters: absence of enlarged superciliary tubercle or projection on the upper eyelid (vs present in M. superciliaris ), generally more granular with numerous small and larger tubercles scattered on dorsum (vs generally more smooth skin with occasional small and low tubercles on dorsum in M. superciliaris ; see Figure 9 View Figure 9 ), presence of a characteristic V-shaped glandular wart in scapular area edged with black (vs absent in M. superciliaris ), by longer finger I, which is equal in length to half of finger II (vs shorter in M. superciliaris ), by comparatively less developed webbing (webbing formula I 1–2 II 1–2 III 1–2½ IV 2½–1 V vs I 1–1 II 1–1 III 1–2 IV 2–1 V in M. superciliaris ), and by generally more uniform dorsal colouration (vs numerous dark vermiculations, lines and small spots edged with beige or white usually present in M. superciliaris ; see Figure 9 View Figure 9 ).