Micryletta inornata ( Boulenger 1890 ), 1987

Alhadi, Farits, Hamidy, Amir, Farajallah, Achmad, Munir, Misbahul, Atmaja, Vestidhia Y., Garg, Sonali, Biju, S. D. & Smith, Eric N., 2019, Rediscovery of Micryletta inornata (Boulenger, 1890) from Sumatra: redescription, molecular identity, and taxonomic implications, Zootaxa 4613 (1), pp. 111-126 : 117-120

Micryletta inornata ( Boulenger 1890)

Deli Paddy Frog

( Figures 1–4 ; Tables 1–4 )

Original name and description. Microhyla inornata Boulenger 1890 . Proceedings of the Zoological Society of London, 1890: 37. Syntypes. An adult male, NHM 1889.11.12.30 (ex. BMNH 1947.2.11.75), and an adult female, NHM 1889.11.12.4 (ex. BMNH 1947.2.11.74). Type locality. Deli, Sumatra, Indonesia. Current status of specific name. Valid name, as Micryletta inornata ( Boulenger 1890) ( Dubois 1987) .

Specimens examined. Syntypes: An adult male, NHM 1889.11.12.30 (ex. BMNH 1947.2.11.75) , and an adult female, NHM 1889.11.12.4 (ex. BMNH 1947.2.11.74), from “Deli, Sumatra ”, Indonesia . Topotypes : An adult male, MZB Amph 27242, from Suka Makmue , Nagan Raya Regency , Aceh Province , Sumatra, Indonesia (04°09’58.9’’ N, 96°19’44.4’’ E, 71 m a.s.l.) ; an adult male, MZB Amph 8542 from Gumai Pasemah Wildlife Reserve , Lahat Regency , South Sumatra Province, Indonesia (03°58’13.6” S, 103°19’58.5” E, 661 m a.s.l.) ; and eight sub-adults, UTA A-65747 ( SVL 13.3 mm), UTA A-65750 ( SVL 12.6 mm), UTA A-65749 ( SVL 10.2 mm), MZB Amph 23948 ( SVL 12.0 mm), MZB Amph 23947 ( SVL 12.0 mm), MZB Amph 23569 ( SVL 9.1 mm), MZB Amph 23949 ( SVL 9.1 mm), and MZB Amph 23570 ( SVL 13.1 mm), all from Tanjung Morawa , Deli Serdang Regency, North Sumatra Province, Indonesia (03°36’05.2” N, 98°51’31.0” E, 12 m a.s.l.). Morphometric measurements for all adult specimens are provided in Table 2

.

Diagnosis. Micryletta inornata differs from other members of the genus by the combination of following characters: small adult snout-vent size (male SVL 16.8–20.5 mm, N = 3; female SVL 19.5 mm, N = 1), slender body; absence of maxillary and vomerine teeth; finger and toe tips rounded; presence of well-developed subarticular tubercles on all fingers and toes; presence of a small inner metatarsal tubercle and absence of outer metatarsal tubercle on foot; absence of webbing between fingers and toes; dorsum brownish-grey with a silver tinge and irregular blackish-brown blotches of variable size; presence of a discontinuous lateral blackish-brown streak from tip of the snout to near the groin; throat light reddish-grey without prominent spots ( Figure 3 ).

Morphological comparison of male topotype (MZB Amph 27242) with male syntype (NHM 1889.11.12.30). The original description ( Boulenger 1890) mentioned three syntypes (“Three specimens, two males and one female”), all from Professor Moesch’s collection from “Deli, Sumatra ”, Indonesia. Currently only two specimens are available at NHM, London—an adult male, NHM 1889.11.12.30 (ex. BMNH 1947.2.11.75), and an adult female, NHM 1889.11.12.4 (ex. BMNH 1947.2.11.74).

Our collections from the type locality “Deli” (Deli Serdang), Aceh and South Sumatra, Indonesia, are well comparable with the original description of Microhyla inornata Boulenger 1890 (= Micryletta inornata ) in size, colour and markings, and overall morphology. In order to morphologically confirm the identity of our new collections from Sumatra, we compared a topotypic specimen (MZB Amph 27242, male, and/or male MZB Amph 8542; in parenthesis) with various characters stated in the original description (sex of described specimen not stated; in double quotes) along with measurements taken from the syntype specimen/s (NHM 1889.11.12.30, male, and/or NHM 1889.11.12.4, female; in italics). Snout-vent size: “From snout to vent 20 millim”, male NHM 1889.11.12.30, SVL 16.8 mm and female NHM 1889.11.12.4, SVL 19.5 mm (male MZB Amph 27242, SVL 20.5 mm; male MZB Amph 8542, SVL 17.0 mm). Snout length: “shorter than the diameter of the orbit”, male NHM 1889.11.12.30, SL 1.8 mm vs. EL 2.1 mm (male MZB Amph 27242, snout shorter than the diameter of eye, SL 2.1 mm vs. EL 2.3 mm). IUE: “interorbital space a little broader than upper eyelid”, male NHM 1889.11.12.30, IOD 2.1 mm vs. UEW 0.8 mm (male MZB Amph 27242, IOD 2.7 mm vs. UEW 1.1 mm). Relative finger length: “First finger much shorter than second”, male NHM 1889.11.12.30, length of first finger 55.6% of second finger, FL I 1.0 mm vs. FL II 1.8 mm (male MZB Amph 27242, length of first finger 78.9% of second finger, FL I 1.5 mm vs. FL II 1.9 mm). Foot webbing: toes “quite free”, male NHM 1889.11.12.30, webbing between toes absent (male MZB Amph 27242, webbing between toes absent). IMTL: “inner metatarsal tubercle very small, rounded”, male NHM 1889.11.12.30, small and rounded, IMTL 0.4 mm (male MZB Amph 27242, IMTL 0.4 mm). OMTL: “no outer tubercle”, male NHM 1889.11.12.30, outer metatarsal tubercle absent (male MZB Amph 27242, absent). Tibiotarsal articulation: “The tibio-tarsal articulation reaches the eye” (male MZB Amph 27242, tibiotarsal articulation reaches the eye).

Further, since both the syntypes are bleached, reliable comparison of skin characters was only possible between the original description and our new collections from Sumatra ( Figure 3 ). Dorsal colouration and markings of the described specimen dark brown above, spotted or marbled with black; sides of the head black, with a series of white spots along with the upper lip; lower parts brown; throat of male black match our new collections with limited variations in dorsal black spots and blotches ( Figure 3 ).

Hence, we conclude that our new collections from Deli Serdang, Aceh and South Sumatra unambiguously match with the original description and syntype specimens of Micryletta inornata ( Boulenger 1890) . Below we provide a detailed description of a topotype specimen (male, MZB Amph 27242) from Aceh, in order to establish a better understanding of the species and facilitate future comparison.

Description of topotype, male, MZB Amph 27242 (measurements in mm). A small-sized Micryletta (SVL 20.5); head wider (HW 5.7) than long (HL 5.1); snout nearly rounded in dorsal and ventral view, acute in lateral view, its length (SL 2.1) slightly shorter than horizontal diameter of the eye (EL 2.3); loreal region acute with round- ed canthus rostralis; interorbital space flat, wider (IOD 2.7) than the upper eyelid (UEW 1.1) and internarial distance (IND 1.4); distance from nostril to tip of snout (S–NL 0.7) shorter than distance from nostril to the eye (N–EL 1.5); tympanum diameter (TD 0.7) shorter than eye length (EL 2.3); distance from nostril to the eye (N-EL 1.5) longer than distance from tympanum to the eye (T-EL 0.4); internarial distance (IND 1.4) shorter than interorbital distance (IOD 2.7); tympanum weakly-developed, supratympanic fold extending from posterior corner of eye to the shoulder weakly-developed; vomerine teeth absent; tongue small, oval, without papillae.

Forelimbs slender, length (FLL 13.2), forearm (FAL 4.4) shorter than hand length (HAL 5.0); lower arm and hand length (LAL 9.6), longer than hand length (HAL 5.0); relative length of fingers: I<II<IV<III (FL I 1.5, FL II 1.9, FL III 3.0, FL IV 2.0); fingers free of webbing; supernumerary tubercle prominent; nuptial pad absent; subarticular tubercles well developed, rounded, all present; three palmar tubercles: inner palmar tubercle oval (IPTL 0.4), smaller than outer palmar tubercle (OPTL 0.5); tips of all fingers rounded, slightly dilated.

Hindlimbs slender, length (HLL 29.7); tibia slightly longer (TL 9.2) than foot length (FL 8.9); relative length of toes: I<II<V<III<IV; tips of toes rounded, dilated; supernumerary tubercles absent; subarticular tubercles well developed; toes free of webbing; inner metatarsal tubercle present, outer metatarsal tubercle absent.

Skin. Skin of dorsum smooth to shagreened, covered with small scattered tubercles; ventral surfaces smooth.

Colour. Considerable colour differences exist between adults and sub-adults.Adult male, in life. Dorsum brownish-grey with a silver tinge and irregular blackish-brown blotches of variable size; upper eyelids and snout with a greenish-tinge; discontinuous blackish-brown lateral streak from tip of the snout to near the groin; lateral surfaces of belly light brown with greyish-white spots; flanks light brown with blackish-brown spots; silvery-grey line along the margins of upper lip; fore- and hind limbs brownish-grey with irregular light brown spots and blotches; fingers III and IV, and toes IV and V brownish-grey with faint cross bands; fingers I and II, and toes I–III light violet grey; iris bicoloured, light golden brown anteriorly and dark brown posteriorly. Ventrally, throat light reddish-grey with blackish-brown margins (calling male); chest and belly light reddish-grey with faint light grey scattered spots especially towards the margins; fore- and hindlimbs light violet grey. Adult male, in preservation. Dorsum brownish-grey with irregular dark brown blotches of variable size; discontinuous dark brown lateral streak from tip of the snout to near the groin; lateral surfaces of belly light brown with grey spots; fore- and hind limbs light grey with irregular light brown spots and blotches. Ventrally, throat light brown with dark brown margins; chest and belly light greyish-brown with faint grey scattered spots especially towards the margins; fore- and hindlimbs light greyish-brown. Sub-adult (MZB Amph 23570), in life. Dorsum, including fore- and hindlimbs, violet grey, light grey or dark grey with irregular golden yellow spots; lateral surfaces of head and belly blackish-brown; margins of upper lip with white spots; a light golden yellow streak extending from either side of the snout running up to the posterior end of upper eyelids; dorsal margins of snout and flanks dark brown with yellowish-grey spots. Ventrally, throat flesh white; chest flesh red with scattered white spots; belly flesh white; fore- and hind limbs light flesh red with a light violet tinge ( Figure 3 ).

Variations. MZB Amph 8542: Dorsal and lateral markings less prominent and lighter in colour compared to MZB Amph 27242.

Morphological comparison. Micryletta inornata cannot be confused with any other known microhylid frog found in the region due to a combination of characters such as small snout-vent size (<SVL 20.5 mm), finger and toe tips rounded without dorso-terminal grooves, absence of webbing between fingers and toes, presence of inner metatarsal tubercle and absence of outer metatarsal tubercle. This species is also the only known member of the genus Micryletta currently known to occur in Sumatra, and could presumably also be endemic to the island. There are currently no available synonyms under M. inornata that originate from Sumatra.

Since Micryletta inornata is the type species of the genus, in order to facilitate future studies, a comparison with all known members of the genus is provided below. A detailed comparison of morphological characters is also tabulated in Table 4 .

Micryletta inornata differs from M. steinegeri by its smaller snout-vent size in males, SVL 16.8–20.5 mm, N = 3 (vs. SVL 23.0–24.0 mm, N = 3); tibiotarsal articulation of adpressed limb reaching up to the level of eye (vs. reaching up to the level of tympanum); webbing between toes absent (vs. rudimentary webbing); dorsum brownishgrey with a silver tinge (vs. dark grey to violet, based on Poyarkov et al. [2018]); and ventral surfaces light reddishgrey without mottling (vs. with mottling).

Micryletta inornata differs from M. erythropoda (based on Tarkhnishvili 1994; Poyarkov et al. 2018) by its smaller snout-vent size in males, SVL 16.8–20.5 mm, N = 3 (vs. SVL up to 30 mm); tibiotarsal articulation of adpressed limb reaching up to the level of eye (vs. reaching up to the level of posterior edge of tympanum); outer metatarsal tubercle absent (vs. present); webbing between toes absent (vs. rudimentary webbing); dorsum brownish-grey with a silver tinge (vs. grey or beige to saturated ochre or brick-red); dorsum with irregular blackish-brown blotches of variable size (vs. irregular dark spots); flank light brown with blackish-brown spots (vs. dark brown to grey with white patches); and ventral surfaces light reddish-grey without mottling (vs. with mottling).

Micryletta inornata differs from M. nigromaculata (based on Poyarkov et al. 2018) by its relatively smaller snout-vent size in male, SVL 16.8–20.5 mm, N = 3 (vs. 18.5–23.3 mm, N =18); supratympanic fold weakly developed (vs. well developed, thick and granular); dorsal skin smooth, covered with small scattered tubercles (vs. slightly granular with small round flattened tubercles); dorsum brownish-grey with a silver tinge (vs. brown to reddish-brown); hourglass-shape marking on dorsum absent (vs. irregular hourglass-shaped marking bordered by orange line present); flank light brown with blackish-brown spots (vs. brown with dark patches or spots edged with white), and ventral surface light reddish-grey without mottling (vs. whitish with grey mottling).

Apart from comparison with all the currently recognised species, we compare Micryletta inornata with another available taxon currently under its synonymy. Microhyla inornata lineata Taylor 1962 (= Micryletta inornata lineata ) was originally described as a subspecies from Nakhon Si Thammarat, Thailand. Based on morphological characters stated in the original description ( Taylor 1962), Micryletta inornata inornata differs from M. inornata lineata by its tibiotarsal articulation of adpressed limb reaching up to the level of eye (vs. below the eye); and dorsum with irregular blackish-brown blotches of variable size (vs. dorsum with nearly continuous longitudinal stripes).

Natural history. All specimens in the present study were collected from lowland secondary forests (Aceh and South Sumatra) and oil palm plantations (Deli Serdang) at elevations of 12–661 m a.s.l. The specific habitat where the individuals were located comprised of several temporary ponds.All individuals were found sitting on grass blades about 10–20 cm above the ground. During our surveys in January 2014 and June 2016, none of the male individuals were found calling and no tadpoles were observed in the temporary ponds. Other species observed at the sampling locality included Microhyla heymonsi , Pulchrana glandulosa , Phrynoidis asper and Limnonectes macrodon .

Distribution. Micryletta inornata is currently known only from three localities in Sumatra Island, Indonesia: (1) Tanjung Morawa in Deli Serdang Regency (“Deli”), North Sumatra Province; (2) Suka Makmue in Nagan Raya Regency, Aceh Province; and (3) Gumai Pasemah Wildlife Reserve in Lahat Regency, South Sumatra Province ( Figure 1 ).

Figures

FIGURE 1. The revised distribution of Micryletta inornata based on new locality records from Sumatra. Genetically and morphologically studied M. inornata samples (red); an additional morphologically studied M. inornata sample (green); and previously misidentified M. ‘inornata’ populations used for the molecular study (blue). The locality numbers are referenced in Table 1.

FIGURE 2. Maximum Likelihood tree for 19 samples of the genus Micryletta based on ~435 bp fragment of the mitochondrial 16S rRNA gene. Values at the branches indicate Maximum Likelihood Bootstrap Support (MLBS) and Bayesian Posterior Probabilities (BPP), respectively.

FIGURE 3. Micryletta inornata from Sumatra in life. A–B. Adult male (MZB Amph 27242 from Aceh): A. dorsolateral view; B. ventral view. C–D. Sub-adult (MZB Amph 23570 from Deli Serdang): C. dorsolateral view; D. ventral view.

FIGURE 4. Micryletta inornata, syntype (male, NHM 1889.11.12.30) and topotype (male, MZB Amph 27242). A–E. Syntype, in preservation: A. dorsal view; B. ventral view; C. lateral view of head; D. ventral view of hand; E. ventral view of foot. F–J. Topotype, in preservation: F. dorsal view; G. ventral view; H. lateral view of head; I. ventral view of hand; J. ventral view of foot. Scale bars = 5 mm.