Seven new species of Hypselostomatidae are described from the Chinese province Guangxi: Angustopila dominikae Páll-Gergely & Hunyadi, sp. n., A. fabella Páll-Gergely & Hunyadi, sp. n., A. subelevata Páll-Gergely & Hunyadi, sp. n., A. szekeresi Páll-Gergely & Hunyadi, sp. n., Hypselostoma socialis Páll-Gergely & Hunyadi, sp. n., H. lacrima Páll-Gergely & Hunyadi, sp. n. and Krobylos sinensis Páll-Gergely & Hunyadi, sp. n. The latter species is reported from three localities. All other new species are known only from the type locality. Specimens nearly identical to the type specimens of Angustopila huoyani Jochum, Slapnik & Páll-Gergely, 2014 were found in a cave in northern Guangxi, 500 km from the type locality. Adult individuals of Angustopila subelevata sp. n. (shell height = 0.83–0.91 mm, mean = 0.87 mm) and A. dominikae sp. n. (shell height of the holotype = 0.86 mm) represent the smallest known members of the Hypselostomatidae, and thus are amongst the smallest land snails ever reported. We note that Pyramidula laosensis Saurin, 1953 might also belong to Krobylos. Paraboysidia neglecta van Benthem Jutting, 1961, which was previously included in Angustopila, is classified in Hypselostoma.

A review of the microgastropod genus Systenostoma is provided. Thai and Malaysian species are transferred to a new genus, Angustopila (type species: Systenostoma tamlod Panha & Burch 1999). A new subterranean Angustopila species is described here. Conchologically, the new species is most similar to the cave-dwelling, Thai A. tamlod (Panha & Burch, 1999). One Thai species (Systenostoma edentata) is transferred to the genus Hypselostoma. Vietnamese members remain in the genus Tonkinospira (nomen novum) for Systenostoma Bavay & Dautzenberg 1908 (non Systenostoma Marsson 1887). A comprehensive map of former Systenostoma species is presented. SEM and NanoCT images, including a video of A. huoyani sp. n. internal shell morphology, provide novel perspectives of the shells of Angustopila and of the scarcely known Vietnamese Tonkinospira species. The biology of these snails is not yet known but collection localities suggest a troglophilic ecology.

Two new, extremely small land snail species, Angustopila coprologos Páll-Gergely, Jochum & Hunyadi n. sp. and Angustopila psammion Páll-Gergely, Vermeulen & Anker n. sp. are described from northern Vietnam and northern Laos, respectively. The former is characterized by a rough surface sculpture and bears tiny mud granules arranged in a pattern of radial lines on its shell surface. The latter species is the new global record-holder of the tiniest land snail title, with a shell width of 0.6–0.68 mm and a shell height of 0.46–0.57 mm. These measurements surpass the former records of Angustopila pallgergelyi and Acmella nana.

The Southeast Asian genusAngustopila, 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.Angustopilais 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. akrodonPáll-Gergely & Hunyadi,sp. nov.,A. apiariaPáll-Gergely & Hunyadi,sp. nov.,A. apiostomaPáll-Gergely & Vermeulen,sp. nov.,A. apokritodonPáll-Gergely & Hunyadi,sp. nov.,A. antidomedonPáll-Gergely & Hunyadi,sp. nov.,A. babelPáll-Gergely & Vermeulen,sp. nov.,A. bathyodonPáll-Gergely & Hunyadi,sp. nov.,A. bidentataPáll-Gergely & Jochum,sp. nov.,A. cavicolaPáll-Gergely & Dumrongrojwattana,sp. nov.,A. cicatricosaPáll-Gergely & Vermeulen,sp. nov.,A. coprologos uninodusPáll-Gergely & Grego,ssp. nov.,A. erawanicaPáll-Gergely & Dumrongrojwattana,sp. nov.,A. fratermajorPáll-Gergely & Vermeulen,sp. nov.,A. fraterminorPáll-Gergely & Vermeulen,sp. nov.,A. gracilisPáll-Gergely & Hunyadi,sp. nov.,A. halongensisPáll-Gergely & Vermeulen,sp. nov.,A. hyronPáll-Gergely & Vermeulen,sp. nov.,A. maasseniPáll-Gergely & Vermeulen,sp. nov.,A. majusculaPáll-Gergely & Hunyadi,sp. nov.,A. margaritarionPáll-Gergely & Hunyadi,sp. nov.,A. megastomaPáll-Gergely & Vermeulen,sp. nov.,A. occidentalisPáll-Gergely & Hunyadi,sp. nov.,A. oostomaPáll-Gergely & Vermeulen,sp. nov.,A. papaverPáll-Gergely & Hunyadi,sp. nov.,A. parallelaPáll-Gergely & Hunyadi,sp. nov.,A. prolixaPáll-Gergely & Hunyadi,sp. nov.,A. pusillaPáll-Gergely & Hunyadi,sp. nov.,A. pustulataPáll-Gergely & Hunyadi,sp. nov.,A. quadridensPáll-Gergely & Vermeulen,sp. nov.,A. raraPáll-Gergely & Hunyadi,sp. nov.,A. reticulataPáll-Gergely & Hunyadi,sp. nov.,A. somsakiPáll-Gergely & Hunyadi,sp. nov.,A. steffekiPáll-Gergely & Grego,sp. nov.,A. tetradonPáll-Gergely & Hunyadi,sp. nov.,A. thersitesPáll-Gergely & Vermeulen,sp. nov.,A. tonkinospiroidesPáll-Gergely & Vermeulen,sp. nov.,A. tridentataPáll-Gergely & Hunyadi,sp. nov.,A. tweedieiPáll-Gergely & Hunyadi,sp. nov.,A. uvulaPáll-Gergely & Hunyadi,sp. nov.,A. vandevenderiPáll-Gergely & Jochum,sp. nov.,A. vitrinaPáll-Gergely & Hunyadi,sp. nov.,A. vomerPáll-Gergely & Hunyadi,sp. nov.,A. werneriPáll-Gergely & Hunyadi,sp. nov.Angustopila subelevataPáll-Gergely & Hunyadi, 2015 is moved to the synonymy ofAngustopila elevata(F. G. Thompson & Upatham, 1997), andA. singuladentisInkhavilay & Panha, 2016 is a junior synonym ofA. fabellaPáll-Gergely & Hunyadi, 2015. Three species, namelyA. elevata,A. fabellaandA. 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 ofA. erawanicasp. nov.is described.

Current biodiversity patterns are considered largely the result of past climatic and tectonic changes. In an integrative approach, we combine taxonomic and phylogenetic hypotheses to analyze temporal and geographic diversification of epigean (Carychium) and subterranean (Zospeum) evolutionary lineages in Carychiidae (Eupulmonata, Ellobioidea). We explicitly test three hypotheses: 1) morphospecies encompass unrecognized evolutionary lineages, 2) limited dispersal results in a close genetic relationship of geographical proximally distributed taxa and 3) major climatic and tectonic events had an impact on lineage diversification within Carychiidae.