Five times over: 42 new Angustopila species highlight Southeast Asia's rich biodiversity (Gastropoda, Stylommatophora, Hypselostomatidae).

The Southeast Asian genus Angustopila, currently comprising 13 nominal species, encompasses the world's tiniest land snails. This work shows that there are far more species than previously suspected, and that this genus is in fact, a very speciose group of tiny snails widely distributed in Southeast Asia. Angustopila is revised based on type material of known species as well as 211 samples newly collected in China, Laos, Myanmar, Thailand and Vietnam. Altogether, 53 species and one subspecies are recognised, of which 42 species and subspecies are new to science: A.akrodon Páll-Gergely & Hunyadi, sp. nov., A.apiaria Páll-Gergely & Hunyadi, sp. nov., A.apiostoma Páll-Gergely & Vermeulen, sp. nov., A.apokritodon Páll-Gergely & Hunyadi, sp. nov., A.antidomedon Páll-Gergely & Hunyadi, sp. nov., A.babel Páll-Gergely & Vermeulen, sp. nov., A.bathyodon Páll-Gergely & Hunyadi, sp. nov., A.bidentata Páll-Gergely & Jochum, sp. nov., A.cavicola Páll-Gergely & Dumrongrojwattana, sp. nov., A.cicatricosa Páll-Gergely & Vermeulen, sp. nov., A.coprologosuninodus Páll-Gergely & Grego, ssp. nov., A.erawanica Páll-Gergely & Dumrongrojwattana, sp. nov., A.fratermajor Páll-Gergely & Vermeulen, sp. nov., A.fraterminor Páll-Gergely & Vermeulen, sp. nov., A.gracilis Páll-Gergely & Hunyadi, sp. nov., A.halongensis Páll-Gergely & Vermeulen, sp. nov., A.hyron Páll-Gergely & Vermeulen, sp. nov., A.maasseni Páll-Gergely & Vermeulen, sp. nov., A.majuscula Páll-Gergely & Hunyadi, sp. nov., A.margaritarion Páll-Gergely & Hunyadi, sp. nov., A.megastoma Páll-Gergely & Vermeulen, sp. nov., A.occidentalis Páll-Gergely & Hunyadi, sp. nov., A.oostoma Páll-Gergely & Vermeulen, sp. nov., A.papaver Páll-Gergely & Hunyadi, sp. nov., A.parallela Páll-Gergely & Hunyadi, sp. nov., A.prolixa Páll-Gergely & Hunyadi, sp. nov., A.pusilla Páll-Gergely & Hunyadi, sp. nov., A.pustulata Páll-Gergely & Hunyadi, sp. nov., A.quadridens Páll-Gergely & Vermeulen, sp. nov., A.rara Páll-Gergely & Hunyadi, sp. nov., A.reticulata Páll-Gergely & Hunyadi, sp. nov., A.somsaki Páll-Gergely & Hunyadi, sp. nov., A.steffeki Páll-Gergely & Grego, sp. nov., A.tetradon Páll-Gergely & Hunyadi, sp. nov., A.thersites Páll-Gergely & Vermeulen, sp. nov., A.tonkinospiroides Páll-Gergely & Vermeulen, sp. nov., A.tridentata Páll-Gergely & Hunyadi, sp. nov., A.tweediei Páll-Gergely & Hunyadi, sp. nov., A.uvula Páll-Gergely & Hunyadi, sp. nov., A.vandevenderi Páll-Gergely & Jochum, sp. nov., A.vitrina Páll-Gergely & Hunyadi, sp. nov., A.vomer Páll-Gergely & Hunyadi, sp. nov., A.werneri Páll-Gergely & Hunyadi, sp. nov. Angustopilasubelevata Páll-Gergely & Hunyadi, 2015 is moved to the synonymy of Angustopilaelevata (F. G. Thompson & Upatham, 1997), and A.singuladentis Inkhavilay & Panha, 2016 is a junior synonym of A.fabella Páll-Gergely & Hunyadi, 2015. Three species, namely A.elevata, A.fabella and A.szekeresi, are widespread over several hundred kilometres while some other species (A.huoyani, A.parallelasp. nov., A.cavicolasp. nov.) are known from just two sites a few hundred kilometres apart. All others are small range or single-site endemics. The reproductive anatomy of A.erawanicasp. nov. is described.