Mysterious Narrow-Mouthed Frog
Species Description: Garg S, Biju SD 2019 New microhylid frog genus from Peninsular India with Southeast Asian affinity suggests multiple Cenozoic biotic exchanges between India and Eurasia. Scientific Reports 9:1906
The arms are long but the forearms are shorter than the hand. There are three prominent palmer tubercles and numerous supernumerary tubercles. Both the inner and middle palmer tubercles are rounded while the outer palmar tubercle is oval. The relative finger lengths are I < IV < II < III and end in tips with small discs. The fingers have no fringes or webbing, but do have well-developed and rounded subarticular tubercles, alternating with additional smaller tubercles. In males, the nuptial pad on finger I is absent (Garg and Biju 2019).
The hindlimbs are also long with the thigh being shorter than the shank and the foot. The prominent inner metatarsal tubercle is oval while the small outer tubercle is rounded. The toes are long with relative lengths of I < V < II < III < IV and also end in rounded tips with small discs. Unlike the fingers, the toes have weakly developed dermal fringes and rudimentary webbing. The toes have supernumerary tubercles and prominent, oval subarticular tubercles alternated with smaller tubercles (Garg and Biju 2019).
The skin on the dorsum is generally shagreen. The snout and upper eyelids have scattered granular projections. There are more prominent granular projections on the upper and lower parts of flanks and anterior and posterior parts of the dorsum. The dorsal parts of the limbs also have granular projections. The skin around the anal region are prominently granular. The ventral surfaces of the throat is finely granular while the chest, belly, and limbs are smooth with granular projections (Garg and Biju 2019).
At Gosner stage 34, the tadpoles of M. franki have a total length of 28.8 mm and a snout-vent length of 8.98 mm. The body height is 5.32 mm, the body width of 6.51 mm, and vent-to-tail length is 19.8 mm. The bodies are bulbous, with a narrower and shorter anterior region and a wider and longer posterior region. The snout is rounded with narial depressions closer to the snout tip than eyes. The nostrils are closely spaced with a distance of 1.24 mm. The eyes are small, bulbous, and laterally positioned with a distance of about 5.36 mm. The mouth appears as a slit opening, and no oral disc is present. No jaw sheaths and papillae are seen, and the mouth also lacks keratodonts. The tadpole has a short, tubular sinistral spiracle with the opening located above the ventral tail musculature margin. The tubular vent is located ventrally and medially with the opening in line with the ventral fin. The tail musculature was bilaterally divided with unequal tail membranes on either side. At the distal end, the tail tapers, ending in a whip-like flagellum. The tail musculature ends halfway along the tail, leaving a weak trail of muscles extending up to the tail tip. The dorsal fins begin near the tail-body junction, and the margin of the lower fin is not parallel to the margin of the tail muscle. The maximum tail height is 6.30 mm with the tail musculature height is 5.98 mm. The tail width is 1.96 mm (Garg and Biju 2019).
At the time of its description, M. franki was the only member of the new genus, Mysticellus. It can be distinguished from other members of its family, Microhylidae, by hand musculature. Other morphological characters differentiate M. franki from individual genera. More specifically, M. franki can be distinguished from frogs in the genus Glyphoglossus by the former having a slenderer body, horizontal pupils, and well-developed hand tubercles. It can be distinguished from Kaloula frogs by the focal species having a smaller adult snout-vent length, lacking a ridge on the posterior sides of the choanae, lacking a supratympanic fold, having smaller digit discs, and having a smaller inner metatarsal tubercle. It differs from Metaphrynella by M. franki lacking a ridge on the posterior sides of the choanae, having smaller digit discs, lacking finger webbing, preferring terrestrial habit, and breeding around temporary water puddles. Mysticellus franki is differentiated from Microhyla by having a linearly shaped body, having dark blackish-brown “false-eye” lateral spots, and having prominent subarticular tubercles that alternate with smaller tubercles. Unlike Micryletta, M. franki has externally indistinct tympanum, and “false-eye” spots in the lateral region. From Phrynella, M. franki is distinguished by having smaller digit discs, separated metatarsal tubercles, and less toe webbing. Lastly, from Uperodon, M. franki is diagnosed by its slender body, lacking a ridge on the posterior sides of the choanae, having prominent subarticular tubercles that alternate with smaller tubercles, having dark blackish-brown “false-eye” lateral spots, smaller digit discs, smaller inner metatarsal tubercles, and less toe webbing (Garg and Biju 2019).
In life, the dorsal color is dark brick red to reddish-brown. There is a thin, lighter colored mid-dorsal line that extends from the tip of the snout to the vent. The dorsal surfaces of the forearm are light brown while the hand and fingers are reddish-brown. The dorsal surface of the hindlimbs, including the toes, match the dorsal coloration but are patterned with faint greyish-brown transverse bands. The posterior portion of the thigh are light brown. The lateral surfaces of the body from the tip of the snout to the lower abdomen and extending towards the dorsal surface above the hind legs are dark brown, almost black. This patterning forms two prominent blackish-brown ‘false-eye’ like spots on either side. The ventral surfaces of the throat, belly, arms and legs are dark brown with a violet tinge and patterned with various sized greyish-white speckles and blotches. Males have a distinct calling patch on the throat (Garg and Biju 2019).
In preservation, the dorsum is greyish-brown, with the upper eyelids and center of the dorsum being slightly darker greyish-brown. The lateral surfaces remain prominently brownish-black from tip of the snout up to the lower abdomen, maintaining its patterning as in life. The dorsal surface of the forearm is light brown, with the hands and fingers turning a dark greyish-brown. The dorsal surface of the hind limbs, including the toes, are greyish-brown with faint dark brown transverse bands. The ventral surface of the throat is dark greyish-brown, and the chest, belly and limbs are brown to dark brown with various sized off-white speckles and blotches. The ventral surfaces of the forearm and thighs are light brown (Garg and Biju 2019).
In tadpoles, dark pigmentation is visible around the narial depressions (Garg and Biju 2019).
There is some sexual dimorphism with breeding males having a distinct calling patch on their throat. Nuptial pads are absent from finger I. Otherwise, the color and markings are almost identical across all the type specimens with only slight variation in the darkness of the dorsal coloration (Garg and Biju 2019).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Males produce a single type of pulsatile call that is not delivered in groups and have uniform intervals. The 1771.4 ms long call have a rise time of 91.4 ms, a fall time of 1681.9 ms, a pulse rate of 80.2 pulses per second for a total of 141 pulses, and a mean dominant frequency of 3.7 kHz. During the call, males also raise the hind part of their bodies, displaying the prominent “false-eye” markings on their backs (Garg and Biju 2019).
When disturbed, some individuals display similar posterior elevation as calling males, suggesting that this may serve a defensive role against predators (Garg and Biju 2019).
Females lay over 150 pigmented eggs with a diameter of about 1.1 mm, deposited with a large mass of transparent jelly above and below the egg mass. Tadpoles may begin appearing in breeding ponds by the end of July (Garg and Biju 2019).
Maximum Likelihood and Baysesian Inference of mitochondrial 16S rRNA indicate that M. franki is sister to the genus Micryletta. This relationship was also supported by independent analyses using nuclear and mitochondrial datasets (Garg and Biju 2019).
The microhylid genus Mysticellus diverged from its sister lineage Micryletta about 39.7 mya during the Eocene, with the pairwise distances of the mitochondrial 16S rRNA gene sequences showing considerable genetic differentiation of at least 8.2% between the two genera. This split is likely to have occurred as the Indian landmass drifted close to the Myanmar-Malay Peninsula during the Middle and Late Eocene (Garg and Biju 2019).
The genus name Mysticellus is derived from the Latin “mysticus” meaning “mysterious” and “ellus,” a diminutive, in reference to the fact that this small frog remained out of sight despite occurring in nearby areas surrounding human settlements (Garg and Biju 2019).
The species epithet, “franki,” is in honor of evolutionary biologist Prof. Franky Bossuyt of Vrije Universiteit Brussel to recognize his role in global amphibian research and education, particularly for his contribution to the study of Indian amphibians (Garg and Biju 2019).
Garg, S., Biju, S.D. (2019). ''New microhylid frog genus from Peninsular India with Southeast Asian affinity suggests multiple Cenozoic biotic exchanges between India and Eurasia.'' Scientific Reports , 9, 1906. [link]
Originally submitted by: Avi Berger (first posted 2020-06-11)
Edited by: Ann T. Chang (2020-06-12)
Species Account Citation: AmphibiaWeb 2020 Mysticellus franki: Mysterious Narrow-Mouthed Frog <https://amphibiaweb.org/species/8958> University of California, Berkeley, CA, USA. Accessed Dec 8, 2021.
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Citation: AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 8 Dec 2021.
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