Nasutixalus microdiscus (Annandale, 1912) nov. comb.

Chresonymy.

Rhacophorus microdiscus Annandale, 1912: 114.

Rhacophorus (Rhacophorus) microdiscus — Ahl (1931): 57, 121.

Philautus (Kirtixalus) microdiscus — Dubois (1987): 73.

Philautus (Philautus) microdiscus — Bossuyt and Dubois (2001): 40.

Philautus microdiscus — Ahmed et al. (2009): 16.

Comments on taxonomic status.

What is currently known under Philautus microdiscus (Fig. 9) was originally described by Annandale (1912), based on a single specimen (ZSI 16924), as Rhacophorus microdiscus from Kobo in the foothills of Abor (now in Assam; Fig. 1 A). This species has never been reported since its description. Gorham (1974) synonymized this species with Rhacophorus jerdonii (now Nasutixalus jerdonii) but this was not followed by Dubois (1987) and Bossuyt and Dubois (2001). Gorham (1974) was only followed by Sarkar and Ray (2006). Dubois (1987) placed this species in the genus Philautus under the subgenus Kirtixalus. Later, Bossuyt and Dubois (2001) transferred it to the nominotypical subgenus Philautus. However, Garg et al. (2021) questioned the placement of this species in the genus Philautus. Based on molecular data of bush frogs collected from across northeast India, we argue that there are no species of the genus Philautus (sensu stricto) present in this region.

After a review of Annandale’s original description and examination of the holotype (ZSI 16924) we provide the following characters for the holotype: small body size (28.7 mm); presence of vomerine teeth; presence of rudimentary webbing on hand; presence of discs on digits. Annandale (1912) mentioned that the disc on the third finger is less than half of the tympanic diameter, but this may be because the specimen was in a dehydrated state as seen on the sketch provided in the original description); granular abdomen and thighs; subtriangular marking on head; concave stripes on dorsum; crossbars on dorsal surface of limbs (Fig. 9); lateral sides of thighs reddish (based on original description).

The holotype being a small bodied frog (28.7 mm) with a comparatively short rounded snout and discs on the fingers and toes (as with species in Nasutixalus, Philautus, Pseudophilautus, and Raorchestes), from northeast India (as we argue only with Nasutixalus and Raorchestes) with vomerine teeth (absent in Raorchestes) strongly suggests that “ P. microdiscus ” belongs to the genus Nasutixalus Jiang et al., 2016. Species of the genus Nasutixalus (e. g., N. medogensis) are known to occur in the Adi (= Abor) Hills of Arunachal Pradesh (Biju et al. 2016; Yang et al. 2018). During our field surveys over the past five years we recorded several populations of Nasutixalus in the upper reaches of the Adi Hills and throughout the State of Arunachal Pradesh. These recorded specimens partially match Annandale’s description by the following set of characters: dorsally rounded and laterally nearly truncate snout shape, distinct canthus rostralis, presence of vomerine teeth, distinct tympanum, presence of dorsal stripes, presence of dark bar on inter-upper eyelid space, crossbars on limbs, granular belly, discs on fingers, webbing on foot. Thus, we formally transfer Philautus microdiscus to Nasutixalus microdiscus nov. comb. but acknowledge that further studies involving collecting specimens from the type locality or near the type locality of N. microdiscus and including molecular data for phylogenetic comparisons will be necessary to confirm the identity of these records. In addition, the type localities of N. microdiscus and N. medogensis are 90 km apart. Therefore in the light of these new findings, the identity of N. medogensis needs to be verified. Morphometric measurements of holotype of N. microdiscus taken in this study are provided in Table S 11.

Distribution.

In the original description, the type locality was given as “ Kobo, at the base of Abor foothills ”. However, species of the genus Nasutixalus are known to occur above 1000 m elevation, while the elevation of Kobo (present day) is below 150 m a. s. l. (Bossuyt and Dubois 2001). It is possible that the specimens were collected from the hills immediately above Kobo in Adi Hills. Fresh material from the area or DNA from the type specimen will help to resolve the true identity of this species.