A recent study on a group of rough-skinned Gephyromantis frogs from Madagascar (Anura: Mantellidae: Mantellinae) established a new subgenus, Asperomantis, with five described species and one undescribed candidate species. Based on newly collected material from the Bealanana District, we address the taxonomy of this candidate species, and reveal that it consists of two populations with low genetic and morphological divergence but considerable bioacoustic differences that are obvious to the human ear. As a result, we describe some of the specimens formerly assigned to Gephyromantis sp. Ca28 as G. angano sp. n. and assign the remaining specimens from a locality between Bealanana and Antsohihy to a new Unconfirmed Candidate Species, G. sp. Ca29. Gephyromantis angano sp. n. is a small species that strongly resembles G. asper and G. ceratophrys, but it differs from these and all other Gephyromantis species by a unique, clinking advertisement call. The new species may be highly threatened by habitat fragmentation, but at present we recommend it be treated as Data Deficient until more data are available to assess its distribution. We discuss the curious relationship between G. angano sp. n. and G. sp. Ca29, which we suspect may represent a case of incipient speciation. We also identify two additional new Unconfirmed Candidate Species of Gephyromantis based on sequence data from other specimens collected during our surveys in the Bealanana District.