Limnonectes meratusensis, Gonggoli & Shimada & Nishikawa & Matsui & Larson & Smith & Hamidy, 2025

Gonggoli, Ade Damara, Shimada, Tomohiko, Nishikawa, Kanto, Matsui, Masafumi, Larson, Thornton, Smith, Eric N. & Hamidy, Amir, 2025, Unveiling a New Species of Fanged Frog (Amphibia: Anura: Dicroglossidae) from Southeastern Borneo, Indonesia, Species Diversity 30 (2), pp. 177-191 : 180-187

Limnonectes meratusensis sp. nov. [New English name: Meratus’ Creek Frog] [New Indonesian name: Bangkong-tuli Meratus] ( Figs 3–9 )

Holotype. MZB Amph 33611, an adult male from Karuh River , Mt. Halau-Halau , at Juhu Village , Batang Alai Timur District, Hulu Sungai Tengah Regency, South Kalimantan Province, Indonesia (2.674277°S, 115.610196°E, elevation 568 m a.s.l.), collected by Tomohiko Shimada, Muhammad Alif Fauzi, and Huda Wiradarma on 15 September 2018.

Paratypes. In total 26 specimens were examined. Four individuals collected by Tomohiko Shimada, Ahmad Nabil Faturahman, and Huda Wiradarma from Mt . Halau-halau, Batang Alai Timur District , Hulu Sungai Tengah Regency , South Kalimantan Province, Indonesia: MZB Amph 33612, an adult female collected with holotype; MZB Amph 33613– 33615, two adult females and one adult male from Jumantir, Juhu Village (2.684793°S, 115.615065°E, elevation 997 m a.s.l.), collected on 16 September 2018 . Nineteen individuals by Tomohiko Shimada, Kanto Nishikawa, Muhammad Alif Fauzi, and Ari Ardianto, from Mt . Halau-halau, Batang Alai Timur District , Hulu Sungai Tengah Regency , South Kalimantan Province, Indonesia: KUHE 61012 and MZB Amph 33616, 33617, three adult females from Karuh River , Juhu Village (2.674277°S, 115.610196°E, elevation 568 m a.s.l.), collected on 8 March 2019; KUHE 61031–61033 , KUHE 61035–61038 , 61043 , and MZB Amph 33619–33621, seven adult females and four adult males, from Jumantir, Juhu Village (2.684793°S, 115.615065°E, elevation 997 m a.s.l.), collected on 9 March 2019; KUHE 61056 , 61057 and MZB Amph 33623, 33624, three adult males and one adult female, from Limau River , Juhu Village (2.697859°S, 115.618198°E, elevation 1299 m a.s.l.), collected on 11 March 2019; MZB Amph 33625, adult male, from Jumantir, Juhu Village (2.684793°S, 115.615065°E, elevation 997 m a.s.l.), collected on 13 March 2019 . Three individuals, MZB Amph 31570, 31571 and MZB Amph 31581, two adult males and one adult female, from Mt . Lumut, Long Sayo Village, Muara Komam District , Paser Regency, East Kalimantan Province, Indonesia (1.413310°S, 115.97675°E, 681 m a.s.l.; 1.415472°S, 115.978611°E, 571 m a.s.l.; 1.415139°S, 115.976278°E, 617 m a.s.l., respectively), collected by Misbahul Munir and Thornton Larson on 12–13 November 2016 .

Etymology. The specific name meratusensis is a toponym referring to the Meratus Mountain Range, where the species is known.

Diagnosis. Based on molecular analyses, Limnonectes meratusensis sp. nov. is nested within the L. kuhlii complex and can be diagnosed from its congeners by the following combination of morphological characteristics: (1) tympanum indistinct; (2) toes fully webbed; (3) cephalic humps present; (4) dorsal skin relatively smooth and with radiating network of low wrinkles; (5) skin at base of tibia with low and scattered small warts; (6) second finger longer than first; (7) pineal spot absent; (8) nuptial pad with minute asperities; (9) dorsum with double band pattern; (10) medium-size (SVL 44.6–64.5 mm in males, 43.2–62.4 mm in females); (11) female head short, RHL 37.4%–40.9% SVL; (12) webbing on inner and outer of the fourth toes moderately excised.

Description of the holotype. Adult male (SVL 52.8 mm), habitus stocky; head relatively longer (HL 24.7 mm, 47.1% SVL) than wide (HW 23.3 mm, 44.1% SVL); cephalic humps present; rostrum longer (RL 7.6 mm, 14.4% SVL) than eye (ED 6.9 mm, 13.1% SVL); nostril dorsolaterally below canthus, closer to snout tip (N-SL 3.0 mm, 5.8% SVL) than to eye (E-NL 3.7 mm, 6.9% SVL); internarial distance (IND 4.7 mm, 8.9% SVL) shorter than interorbital distance (IOD 5.3 mm, 10.0% SVL); snout rounded in lateral view; canthus slightly angular; lore concave; pineal spot indistinct; tympanum indistinct; pair of odontoid processes (tooth-like projections) on lower jaw, tusk-like in profile ( Fig. 5A ); vomerine teeth in oblique groups, behind anterior rims of choanae, groups separated each other by one-fourth length of one group; vocal sac and vocal slits absent.

Forelimb stout, short (FLL 27.2 mm, 51.4% SVL); fingers moderately slender, I<II <IV <III ( Fig. 4 ), second (2FL 10.1 mm, 19.2% SVL) longer than first (1FL 9.5 mm, 18.0% SVL); finger webbing absent; fingers tips bluntly round- ed, without circummarginal grooves; disk of third finger (3TDW 1.36 mm, 2.6% SVL) not much wider than basal phalanx; inner palmar tubercle oval and low (IPTL 3.2 mm, 6.1% SVL); middle palmar tubercle indistinct; outer palmar tubercle slightly oval and elongated, contacting with middle palmar tubercle; proximal subarticular tubercle slightly rounded and elevated; distal subarticular tubercle oval and elongated; skin flaps on second and third fingers present, poorly developed on outer side of third finger; supernumerary metacarpal tubercles absent.

Hindlimb stout, short (HLL 80.7 mm, 153.1% SVL), about two times length of forelimb; toes length formula I<II <V <III <IV; foot (FL 25.1 mm, 47.5% SVL) slightly longer than tibia (TL 24.3 mm, 46.0% SVL); thigh (THL 26.9 mm, 51.0% SVL) longer than tibia; tibio-tarsal articulation reaching between eye and snout; toes tips blunt, rounded; disk of fourth toe (4TDW 1.9 mm, 3.6% SVL) much wider than basal phalanx; toes fully webbed, extending to the disk, webbing formula I 0–0 II 0–0 III 0–0 IV 0–0 V ( Fig. 4 ); inner and outer webbing of fourth toe moderately excised; skin flaps on outer edge of fifth and inner edge of the first toe present, moveable; proximal subarticular tubercle distinct, slightly rounded; inner metatarsal tubercle elongated (IMTL 4.1 mm, 7.8% SVL); outer-metatarsal tubercle absent.

Dorsal skin relatively smooth, with radiating network of low wrinkles; eyelids wrinkled; transverse fold between posterior margins of eyes weak; dorsolateral fold absent; supratympanic fold present, from eye to above axilla; base of tibia dorsal skin with low scattered warts ( Fig. 5C ); cloaca warty; medial surface of first finger thick, from base to level of subarticular tubercle, forming a nuptial pad covered by minute asperities.

Coloration. In life, dorsum reddish brown, marked with dark confluent double band pattern; head with thick dark interorbital bar; upper and lower lips with three dark bands; throat heavily mottled with dark brown; supratympanic fold and canthus covered by one dark band; finger tips with gray spot; limbs marked dorsally with dark crossbars; abdomen nearly translucent, covered by cream and light gray blotches; thigh ventral surface cream nearly completely covered by light gray blotches. In preservative, body dorsum turns dark brown, translucent skin turns cream, and dark throat spots fade to cream.

Variation. Morphometric variations are listed in Table 2. The males had larger values in RHL and ROH than the females. Type specimens with dark body coloration ( Fig. 3D ) and juvenile ( Fig. 9D ) had an indistinct double band pattern on the dorsum. A female paratype ( MZB Amph 31570) showed a double band pattern resembling a double inverted “ V ” . Males of Limnonectes meratusensis sp. nov. had two types of odontoid processes (see Fig. 8 ): four males with tusk-like tip ( MZB Amph 33611, 33620, 33625, and KUHE 61038 ) and eight males with blunt tips ( MZB Amph 31571, 31581, 33614, 33624, and KUHE 61031 , 61036 , 61056 , 61057 ) . One female ( MZB Amph 33613) had equal head length and head width values . Webbing of the fourth toe in one male ( MZB Amph 33620) and one female ( KUHE 61035 ) only reaches the terminal phalange . In preserved specimens, tibio-tarsal articulation never exceeds tip of snout anteriorly nor the level of eye posteriorly. None of the type specimens had a longitudinal line from the snout to the cloaca.

Morphological comparison. Based on the geographical proximity, we compared the new species with the Sundaland species of the L. kuhlii complex. Limnonectes meratusensis sp. nov. is easily distinguished from its sister species L. cintalubang by having fully webbed toes (vs. third phalange of fourth toe free of webbing), larger body size in females (SVL 43.2–62.4 mm vs. 32.0– 43.1 mm), hidden tympanum (vs. distinct), and a cephalic humps in males present (vs. absent). Limnonectes meratusensis sp. nov. is easily distinguished from other species in the L. kuhlii complex such as L. sinuatodorsalis , L. kong , L. hikidai , L. asperatus , L. rhacodus , and L. deinodon Dehling, 2014 , by having fully webbed of toes (vs. webbing on fourth toe not reaching base of tip).

Limnonectes meratusensis sp. nov. differs from L. nusantara , L. maanyanorum , L. tawauensis , L. barioensis , L. conspicillatus , L. lambirensis , L. mocquardi , L. penerisanensis , L. paginatanensis , L. separatus , L. lanjakensis , L. batulwensis , L. paulyambuni , L. utara , L. selatan , L. sisikdagu , and L. kuhlii , by having much smoother skin, classified as Type III of the dorsal skin of tibia based on Gonggoli et al. (2025) (vs. skin of dorsum and tibia covered by more warts, Type I and II), second finger longer than first (vs. first longer than second, except L. abanghamidi , L. lanjakensis , L. mocquardi , and L. paulyambuni ), present of minute asperities on nuptial pad [vs. absent, except L. abanghamidi , L. barioensis , L. batulawensis , L. separatus , and L. kuhlii (nuptial pad absent)], absent of pineal spot (vs. present, except L. abanghamidi , L. tawauensis , and L. paulyambuni ), and the present of distinct double band pattern on the dorsum (vs. absent, except L. utara ). Limnonectes meratusensis sp. nov. differs from L. mocquardi in that males possess a narrower head (in mean values), RHW 38.6%–44.5% SVL, mean 42.4 (vs. 39.1%– 52.7% SVL, mean 47.5: Matsui et al. 2024). Morphologically, L. meratusensis sp. nov. is similar to L. abanghamidi , which has a similar skin texture, but differs from it by having larger male body size, SVL 44.6–64.5 mm (vs. smaller, SVL 33.6 mm: Matsui et al. 2024), smaller female head length, RHL 37.4%–40.9% SVL (vs. larger, RHL 42.0%–43.3% SVL: Matsui et al. 2024), and webbing on inner and outer of the fourth toes moderately excised (vs. little excised: Matsui et al. 2024).

Call characteristics. We analyzed two calls of a male paratype ( KUHE 61031 ) recorded by Tomohiko Shimada at an air temperature of 21.8°C on 9 March 2019 ( Fig. 7 ) . The frog ( KUHE 61031 ) was calling in the water with its upper body standing above the water surface . The river was small and shallow ditch (width less than 1 m and depth less than 5 cm), and the weather was not rainy . The frog emitted a sound like barking, “wwiikkk.....wekkk...wekkk...wekkk.” Two calls consisted of two types of notes . The first note (“wwiikkk”) was characterized by strong frequency and intensity modulations, showing apparent harmonic structures . The fundamental frequency of this note ascended quickly from 0.5 kHz up to 1.2 kHz and kept stable for a while (approx. 0.05 s) but descended down to 0.5–1.0 kHz at the last part . The dominant frequency in the stable part was about 2.4 kHz, observed in the second harmonics . This note was then followed by several (three to four) weak sub-notes (“wekkk”) without frequency and intensity modulations and harmonic structures . The dominant frequency of those subsequent notes was around 2.5 kHz . Each note was emitted at an interval (between the beginnings of two successive notes) of 0.53– 1.02 s, lasting 0.14– 0.17 s .

Call comparisons. The call characteristics of three species of the L. kuhlii complex from Sundaland have been described [ L. hikidai from Borneo: Matsui and Nishikawa (2014); L. selatan : Matsui et al. (2014a) and L. deinodon : Dehling (2014) from Peninsular Malaysia]. Limnonectes meratusensis sp. nov. is easily differentiated from L. deinodon by its call consisting of two types of notes (vs. single long trill); L. meratusensis sp. nov. differs from L. hikidai by sub-notes consisting of 3–4 notes (vs. sub-notes having single note); L. meratusensis sp. nov. differs from L. selatan by having higher dominant frequency, 2.4–2.5 kHz (vs. lower, 0.5 kHz) and calls consisting of two distinct note types (vs. a single note type).

Larvae. Four tadpoles ( KUHE 61039 A–D) in Gosner stages 36–41 [ TOTL 31.9 – 36.4 (mean = 33.7) mm, HBL= 10.7–12.1 (mean = 11.6) mm] collected on 10 May 2019 from a shallow stream with slow to medium current at Lurus River, Mt . Halau-halau, Jumantir , Batang Alai Timur District, Hulu Sungai Tengah Regency, South Kalimantan, Indonesia (2.685995°S, 115.613465°E, elevation 986 m a.s.l.) were examined . Head and body slightly flattened above, spheroidal below; maximum head body width ( HBW) slightly anterior to level of spiracle 58%–63% TOTL (median = 60% TOTL) of HBL; head body depth ( HBD) 67%– 80% TOTL (median = 78% TOTL) of HBW; snout rounded; eyes dorsolateral, invisible from below; nostril open, dorsal, rim raised, midway between tip of snout and eye; internarial 50%–68% TOTL (median = 61.5% TOTL) of interorbital . Oral disk ventral, emarginate, width 38%–42% TOTL (median = 41% TOTL) of HBW; marginal papillae on upper labium with wide gap; lower labium with a continuous row of papillae, submarginal papillae present; denticles 2/3(1); beaks with black outer margins; outer surface smooth; margin finely serrate; upper beak weekly convex medially; neither beak divided . Spiracle sinistral, tube pointing upward and backward, almost completely attached to body wall . Anal tube dextral, attached to ventral fin; loops of gut visible ventrally even in old larvae . Tail moderately long and lanceolate, both margins weakly convex, tapering gradually to slightly rounded tip in uninjured tail; tail length 175%– 204% TOTL (median = 192% TOTL) of HBL, maximum depth 21%–28% TOTL (median = 24.5% TOTL) of length; dorsal fin origin at posterior end of body, deeper than ventral fin; ventral fin origin continuous to vent; caudal muscle moderately strong, maximum tail width 38%–48% TOTL (median = 43% TOTL) of HBW; muscle depth at anterior one-third of tail 57%–63% TOTL (median = 60% TOTL) of tail depth, steadily narrowed posteriorly, shallower than either fin in distal half of tail . Lateral neuromasts discernible . In life, dorsal and lateral body brown, spotted with clusters of dark pigmentations, forming a wide transverse dorsal band at the end of body; venter transparent, scattered with silver dots; tail scattered with black spots ( Fig. 6A–C ) .

Larval comparisons. There are currently only four species of L. kuhlii complex tadpoles from Borneo that have been described [ L. conspicillatus : Inger (1966), Haas et al. (2022); L. hikidai : Inger (1985) (as Rana laticeps Boulenger, 1882 ); two L. kuhlii complex species described by Malkmus et al. (2002) from Mt. Kinabalu and by Inger (1985) from Sarawak and Sabah (uncertainly assigned to any specific lineage)], and L. kuhlii from Java ( Schijfsma 1932) and two species from Peninsular Malaysia ( L. selatan and L. utara : Matsui et al. 2014a). Limnonectes meratusensis sp. nov. differs from those species by having different denticles, 2/3(1) [vs. 2(2)/3(1) or 2(2)/3(1–2) in L. conspicillatus , L. selatan , L. utara , L. kuhlii complex from Mt. Kinabalu, Sabah, and Sarawak; 2(2)/ 2 in L. hikidai ]. However, Limnonectes meratusensis sp. nov. seemingly has similar denticle with L. kuhlii from Java ( Schijfsma 1932), in which the second series of upper labial denticles is continuous, thus rendering the tadpoles of these species indistinguishable.

Field identification. At present, Limnonectes meratusensis sp. nov. is known only from the Meratus Mountain Range where it is found in sympatry with L. maanyanorum and in syntopy with L. nusantara , the most proximate known localities to that of the new species. All three of these species present with fully webbed toes. Their skin texture, however, is distinctive with the dorsum and tibia covered by numerous warts in L. maanyanorum and L. nusantara vs. smooth in L. meratusensis sp. nov.

Distribution and Natural History. This new species was found in small rocky streams in the primary forests of Mt. Halau-halau and the secondary forests on Mt. Lumut . Individuals were found in the water, or on/under leaf litter on the stream bank (see Fig. 9 ). Specimens from Mt. Halau-Halau were found between 568 and 1299 m a.s.l., while those from Mt. Lumut were found from 571 to 681 m a.s.l. The new species was found sympatrically with: Alcalus baluensis (Boulenger, 1896) ; Ansonia spinulifer (Mocquard, 1890) ; Kalophrynus subterrestris Inger, 1966 ; Leptobrachella fritinniens (Dehling and Matsui, 2013) ; Leptobrachium montanum Fischer, 1885 ; Leptomantis gauni ( Inger, 1966) ; L. finchi ( Inger, 1966) ; L. nusantara ; Metaphrynella sundana (Peters, 1867) ; Nyctixalus pictus (Peters, 1871) ; Odorrana hosii (Boulenger, 1891) ; Pelobatrachus kalimantanensis (Munir, Hamidy, Matsui, Iskandar, Sidik, and Shimada, 2019) ; Meristogenys sp. ; Philautus bunitus Inger, Stuebing, and Tan, 1995 ; Phi. mjobergi Smith, 1925 ; Phi. hosii (Boulenger, 1895) ; Phi. macroscelis (Boulenger, 1896) ; Phrynoidis asper (Gravenhorst, 1829) ; and Staurois guttatus (Günther, 1858) .

Figures

Fig. 3. Dorsolateral, dorsal, and ventral views of Limnonectes meratusensis sp. nov., male holotype, MZB Amph 33611 (A–C), and female paratype, MZB Amph 33612 (D–F). Scale: 10mm. Photographs by Tomohiko Shimada.

Fig. 4. Ventral view of left hand and foot of male holotype of Limnonectes meratusensis sp. nov., MZB Amph 33611. Scale: 5mm. Photographs by Ade Damara Gonggoli.

Fig. 5. Frontal view of the mandible and dorsal view of the tibia of male holotype, MZB Amph 33611 (A, C: 004), and female paratype, MZB Amph 33612 (B, C: 005) of Limnonectes meratusensis sp. nov. Not to scale. Photographs by Tomohiko Shimada.

Fig. 6. Dorsal (A), lateral (B), and ventral (C) views of a tadpole of Limnonectes meratusensis sp. nov. (KUHE 61039A) in stage 40 of Gosner (1960). Scale: 10mm. Photographs by Tomohiko Shimada.

Fig. 7. Call of Limnonectes meratusensis sp. nov. from Jumantir, South Kalimantan, Indonesia, recorded at an air temperature of 21.8°C. Sonogram (top) and waveform (bottom).

Fig. 8. Variation in odontoid processes of males Limnonectes meratusensis sp. nov. showing odontoids, type 1—with a tusk-like tip (top)— and type 2—with a blunt tip (bottom)—. Not to scale. Photographs by Ade Damara Gonggoli.

Fig. 9. Limnonectes meratusensis sp. nov. in life. A, Non-vouchered specimens; B, holotype male, MZB Amph 33611, from Mt. Halauhalau, South Kalimantan; C, female paratype, MZB Amph 31570; D, juvenile non-type, MZB Amph 31582, both from Mt. Lumut, East Kalimantan. The green arrows indicate a distinctive double band pattern on the dorsum. Photographs by Tomohiko Shimada (A, B), Misbahul Munir, and Thornton Larson (C, D).