Abundance in secret: a review of the genus <i>Leptobrachium</i> (Anura, Megophryidae) in India, with descriptions of two new species

Of the 39 currently recognized species in the Slender Armed Frog genus <i>Leptobrachium</i>, four are reported from India, <i>Leptobrachium aryatium, L. bompu</i>, <i>L. smithi</i>, and <i>L. sylheticum</i>. Based on new collections, we review these reported species by integrating molecular, morphological, and behavioral data. Our comparative analyses of external and internal morphology as well as molecular data and acoustic properties reveal two new species-level lineages from the Lower Dibang Valley and Shi Yomi districts of Arunachal Pradesh, India, which we describe here as new species. Phylogenetically, <i>Leptobrachium mechuka</i> <b>sp. nov.</b> and <i>Leptobrachium somani</i> <b>sp. nov.</b> are members of the <i>L. bompu</i> species group, but they are distinct from <i>L. bompu sensu stricto</i> by DNA sequence divergence in the 16S mitochondrial rRNA gene of 3.6-4.2% and 4.5-4.7%, respectively. A population previously identified as <i>L.</i> cf<i>. bompu</i> from Medog County, China, is also assignable to <i>Leptobrachium mechuka</i> <b>sp. nov.</b> Each new species is distinguished from congeners by a combination of diagnostic morphological characters, including in the case of <i>Leptobrachium somani</i> <b>sp. nov.</b>, a unique advertisement call comprising two distinct call types; unicolored silvery white iris; moderately large webbing between toes; and ventral coloration. <i>Leptobrachium mechuka</i> <b>sp. nov.</b> on the other hand, is distinguishable by its head length equal to width; nostril equidistant from the snout tip and the eye; internarial distance equal to the distances from nostril to eye and from nostril to snout tip; distance from the tip of inner metatarsal tubercle to the tip of first toe shorter than the length of inner metatarsal tubercle itself; and frontoparietals separated at the midline by a moderate fontanelle. Analyses of multiple new populations representing members of the <i>L. smithi</i> group reveal that <i>L. smithi</i> is absent from the Indian fauna; all previous records attributed to this species from India instead represent <i>L. aryatium</i> or <i>L. sylheticum</i>. These discoveries highlight the prevalence of taxonomic misidentifications in the absence of detailed systematic studies as well as the underestimation of diversity in the genus <i>Leptobrachium,</i> not only from India but across its known range. Our results underscore the need for dedicated surveys that document amphibian diversity in underexplored regions of Northeast India.