Introduction
The frog family Microhylidae is among the most speciose groups of Anura, comprising 690 species and 12 subfamilies (Frost 2020; Streicher et al. 2020). Much of this diversity is from tropical habitats (Savage, 1973; Van Bocxlaer et al. 2006; Van der Meijden et al. 2007; Kurabayashi et al. 2011). Among the 12 currently recognized subfamilies of microhylids, the subfamily Microhylinae, with 100 species, is widely distributed in South, Southeast, and East Asia (Garg and Biju, 2019; Frost, 2020). Of these Asian lineages, it is the narrow-mouthed frogs of the genus Microhyla Tschudi, 1838 that have the widest distribution and highest diversity, ranging from the Ryukyu Islands (Japan), India, Indochina, the Sunda Shelf, and the Philippines (Matsui et al. 2005; Atmatja et al. 2018). Microhyla currently contains 41 species, seven of them known to occur in Sumatra: M. achatina Tschudi, 1838; M. berdmorei Blyth, 1856; M. fissipes Boulenger, 1884; M. heymonsi Vogt, 1911, M