During a field trip to the western part of the Balkan Peninsula in 2016, investigations of several caves and karstic springs revealed six new gastropod species living in subterranean waters and resulted in some note-worthy faunistic records. Five of the new species are assigned to the genus Paladilhiopsis Pavlović, 1913, namely P. prekalensis sp. n., P. lozeki sp. n., P. szekeresi sp. n., P. wohlberedti sp. n., P. falniowskii sp. n. and one to the genus Plagigeyeria Tomlin, 1930, namely P. steffeki sp. n. New Albania and Kosovo distribution records are given for Iglica illyrica Schütt, 1975, Plagigeyeria zetaprotogona Schütt, 1960, Vinodolia matjasici (Bole, 1961), and the first georeferenced record is given for Saxurinator schlickumi Schütt, 1960. The most important environmental factors influencing habitat selection of these subterranean freshwater gastropods are briefly discussed.

The biospeleological investigations of several cenotes in the eastern region of Yucatán state, Mexico, during January 2018 yielded, among other invertebrates, two new truncatelloid gastropod species described herein as Mexicenoticaxochiigen. n. et sp. n. and Pyrgophorusthompsonisp. n. Both species represent the first record of stygobiont gastropod species from the cenotes of Yucatán indicating the high biodiversity potential of the studied area.

The family Moitessieriidae includes minute dioecious gastropods exclusively inhabiting subterranean waters, including thermal ones. Only empty shells were collected in most species, the vast majority of them are described from their gross shell morphology alone. Several visits to a site are usually required to obtain at least some living individuals. High variability in shell morphology and the lack of diagnostic features, coupled with anticipated high levels of endemism, has resulted in a long list of nominal moitessierid species. Type specimens stored as empty shells omit unambiguous identification and delimitation of species boundaries. Due to inaccessibility of cave animals and consequent lack of material suitable for molecular analysis, the phylogenetic relationships, as well as the taxonomy of the family at genus/species level, are far from being understood. The anatomy of the family is also poorly known and provided only for a few taxa. The distinctness of the Moitessieriidae has sometimes been questioned, and their monophyly not proved. Twelve species of the Balkan Moitessieriidae are considered: two species of Paladilhiopsis, two species of Bythiospeum, six species of Iglica, Costellina turrita and Lanzaia bosnica. The shell morphology of each species, as well as the reproductive system of Paladilhiopsis and Iglica, were analysed. DNA sequences of nuclear histone H3, ribosomal 18S, ribosomal 28S and mitochondrial cytochrome oxidase subunit I (COI) were applied to infer phylogenetic relationships among the taxa. The sequences of Bythiospeum from GenBank have been used to infer relationships between Bythiospeum and Paladilhiopsis that were recently synonymized. Paladilhiopsis and Iglica are distinct, but closely related genera, as is the genus Bythiospeum, which does not occur in the Balkans. Its relationships with both former taxa remain unresolved. The Moitessieriidae are clearly distinct from all other families of the Truncatelloidea, however, their monophyly remains doubtful.

Formosana renzhigangi n. sp. and Serriphaedusa (Gibbophaedusa) gerberi n. sp. are described from Yunnan Province of southern China. Additionally, new occurrence records of Papilliphaedusa kunmingensis (Chen et Zhang, 1999) are provided. The composition and diversity of Yunnan's Clausiliidae fauna, its relation to those of the adjacent zoogeographic regions, and the taxonomic status of the native genera Formosana Boettger, 1877 and Papilliphaedusa Nordsieck, 2003 are discussed.

The position of the southwestern Caucasus as a stygobiotic Mollusca hotspot is confirmed. Molecular data of stygobiotic gastropods revealed the diversity of subfamily Sadlerianinae Szarowska, 2006, inhabiting the subterranean environment of Georgia. In addition to the well-known endemic genera Pontohoratia Vinarski, Palatov & Glöer, 2014 and Motsametia Vinarski, Palatov & Glöer, 2014, five more genera were identified in northwestern Georgia as new to the science: Kartvelobiagen. nov., Imeretiopsisgen. nov., Caucasopsisgen. nov., Caucasogeyeriagen. nov., and Hausdorfeniagen. nov. Additionally, 21 new species were found to inhabit the studied area (Samegrelo, Imereti, Racha regions in Georgia).