Many roads to success: alternative routes to building an economic shell in land snails.

Land snails exhibit an extraordinary variety of shell shapes. The way shells are constructed underlies biological and mechanical constraints that vary across gastropod clades. Here, we quantify shell geometry of the two largest groups, Stylommatophora and Cyclophoroidea, to assess the potential causes for variation in shell shape and its relative frequency. Based on micro-computed tomography scans, we estimate material efficiency through 2D and 3D generalizations of the isoperimetric ratio, quantifying the ratios between area and perimeter of whorl cross-sections (2D) and shell volume and surface (3D), respectively. We find that stylommatophorans optimize material usage through whorl overlap, which may have promoted the diversification of flat-shelled species. Cyclophoroids are bound to a circular cross-section because of their operculum; flat shells are comparatively rare. Both groups show similar solutions for tall shells, where local geometry has a smaller effect because of the double overlap between previous and current whorls. Our results suggest that material efficiency is a driving factor in the selection of shell geometry. Essentially, the evolutionary success of Stylommatophora likely roots in their higher flexibility to produce an economic shell.

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.

An extraordinary new fluvial bdelloid rotifer, Coronistomus impossibilis gen. nov., sp. nov., with adaptations for turbulent flow (Rotifera: Bdelloidea: Coronistomidae fam. nov.).

A new bdelloid rotifer, Coronistomus impossibilis gen. nov., sp. nov. is described from the Hawlings River in Maryland, USA. The new species is a non-swimming sediment dweller that exceeds 550 µm in body length. Its corona is a weakly bilobed ciliated field on the ventral side of the head with lateral borders continuing into mouth. The species has ramate trophi that have on each half three widely spaced major teeth with two interproximal teeth. The foot lacks spurs and ends with a pair of long, thick ventral toes and a medially positioned caudal appendage. The new species lives in microhabitats exposed to turbulent flow and its morphological idiosyncrasies are interpreted as adaptations to reduce the likelihood of getting dislodged by the water. Although the corona morphology and the caudal appendage of the new species are similar to the corresponding traits of some of the species in the family Philodinavidae, the structure of its nonprotrusible trophi and its possession of only two toes (as opposed to four) separate it from all other members of the Philodinavidae. Therefore, a new family, Coronistomidae fam. nov., is erected for the new genus Coronistomus.

The trouble with Adineta vaga (Davis, 1873): a common rotifer that cannot be identified (Rotifera: Bdelloidea: Adinetidae).

My purpose here is to highlight three long-standing problems in the taxonomy of Adineta vaga (Davis, 1873) and its subspecies: 1. The lack of unique morphological criteria to identify the morphological variant (morphovariant) Davis described; 2. The lack of an evolutionarily meaningful subspecies definition applicable to parthenogenetic bdelloid rotifers; 3. The lack of compliance with the applicable articles of the International Code of Zoological Nomenclature (ICZN; https://tinyurl.com/y8f242an) when subspecies are assigned to A. vaga.

A review of Aulacospira Möllendorff, 1890 and Pseudostreptaxis Möllendorff, 1890 in the Philippines (Gastropoda, Pupilloidea, Hypselostomatidae).

The genera Aulacospira and Pseudostreptaxis of the Philippines are revised based on the collections of the Senckenberg Forschungsinstitut und Naturmuseum (Frankfurt am Main, Germany), the Florida Museum of Natural History (USA), and recently collected material. Three new species are described: Aulacospiralens Páll-Gergely & Auffenberg, sp. n., Aulacospirakrobyloides Páll-Gergely & Schilthuizen, sp. n., Pseudostreptaxisharli Páll-Gergely & Schilthuizen, sp. n.

Taxonomic morphology of the genus Adineta (Rotifera: Bdelloidea: Adinetidae) with a new species from a suburban garden.

The morphological descriptions of the species of bdelloid rotifers and the associated taxonomic difficulties, primarily resulting from the inadequate original descriptions of many species, are discussed. The genus Adineta, whose members are relatively easy to study and frequently encountered, is proposed as a starting point for taxonomic revisions of the Bdelloidea. The taxonomically significant morphological traits in the genus Adineta are discussed. Some of these have rarely been used: the number of denticles on the rake organ and body proportions. These traits are used to describe Adineta beysunae sp. nov., which was found in a sample from a house garden. The new species is diagnosed by the morphology of its rump, foot and rake organ. The latter has up to 11 denticles, the highest number recorded in an Adineta species.