Plagiodontes daedaleus (Deshayes, 1851) is the most widespread species in the genus Plagiodontes Doering, 1877. Although some 19th century authors recorded some differences in shell shape between the populations living to the east or to the west of the Pampean Sierras, Argentina, such differences were ignored by later authors. A multivariate statistical analysis on 608 adult shells collected at 29 localities in and around these mountains was used to test if such narratively described shell differences were statistically significant, irrespectively of their taxonomic status. Shells classified as collected from the east or the west of the sierras were correctly identified in 91.9% of the cases by Multivariate Discriminant Analysis, leading to recognizition of two allopatric shell morphologies. These external divergences were found to correspond with anatomical differences in the reproductive system. We conclude that two different, allopatric species were merged under the name Plagiodontes daedaleus in the literature and raise the subspecies Plagiodontes daedaleus strobelii (Doering, 1877) to the specific level. Another subspecies living to west of the sierras, Plagiodontes daedaleus salinicola (Doering, 1877), also showed a simple penis papilla and a non-swollen vagina, which shows that salinicola is not a member of P. daedaleus but rather a population of P. strobelii that does not deserve subspecific status. The taxonomic significance of the presence of either a simple penial papilla or a papilla bearing an accessory lobe was also confirmed for these Plagiodontes species.

Members of the gastropod genus Ferrissia Walker, 1903, have a near-cosmopolitan distribution in freshwater ecosystems. Five North American species, distinguished by conchological, habitat, and distributional details, are generally recognized. However, they can be difficult to diagnose in practice, and we aimed to comprehensively revisit their systematics and taxonomy using molecular phylogenies. Our primary result was congruent for all three genetic markers: two highly distinctive Ferrissia clades, each encompassing multiple nominal species, were widely distributed across North American watersheds in both lentic and in lotic habitats. One clade was restricted to North America and was exclusively composed of lotic F. rivularis (Say, 1817) and lentic F. parallela (Haldemann, 1841). These two taxa exhibited geographic, rather than taxonomic, genetic structuring, strongly implying that they are conspecific and that F. parallela is a junior synonym of F. (Ferrissia) rivularis. The other clade contained three North American taxa, F. fragilis (Tryon, 1863) and putative specimens of F. mcneilli Walker, 1925, and F. walkeri (Pilsbry & Ferriss, 1907), in addition to the Hawaiian F. sharpi (Sykes, 1900), as well as multiple invasive Eurasian founder populations. All four taxa shared overlapping genotypes and shell phenotypes, prompting us to conclude that they are conspecific with F. fragilis having taxonomic priority. This New World species had robust phylogenetic links to Old World congeners, thereby enabling us to unite global septum-forming Ferrissia species under the subgenus Kincaidilla Hannibal, 1912. Ferrissia rivularis and F. fragilis differed in a number of conchological traits, including maximum body size, details of apex positioning and orientation, and the ability to form a septum. The two former traits were sufficient to distinguish sympatric populations.

Diverse biogeographic regions have been proposed in Argentina using different approaches of biogeography and different criteria. However, none of these proposals has considered freshwater gastropods in estimating biodiversity values, although gastropods from continental waters have great ecological importance and are a useful group to characterize freshwater environments. For this reason, our aim is to define freshwater gastropod provinces and to compare them with the available information on biogeographic regions previously defined using other data sets. The gastropod database comprises approximately 4,000 georeferenced records from museum collections, bibliographic records, and collections of our research team. A similarity analysis among basins was carried out using the species as characters and applying Jaccard's coefficient and UPGMA clustering with the MVSP program to obtain the resulting phenogram. Eight provinces were identified: I, Misionerean; II, Middle Paraná; III, Uruguay River; IV, Lower Paraná — Río de la Plata; V, Central; VI, Cuyo; VII, Northern Patagonia; and VIII, Southern Patagonia. Between Provinces V and VI lies a Transitional Zone that shows a higher faunal similarity with the Del Plata basin than with the Patagonian basins. The provinces with the highest diversity were I and IV (H = 1.92 and 1.89 respectively), while Province III shows the highest richness (S = 51) and quantity of endemic and vulnerable species. These provinces are the most densely populated in the country and therefore include the areas with the highest environmental degradation level.

Two new species are described based on material from the Late Miocene Paraná Formation, Entre Ríos, Argentina: Polymesoda muravchiki, nov. sp., and Erodona doellojuradoi, nov. sp. The bearing rocks were deposited during the Entrerriense ingression that covered part of central-northern Argentina, reaching as far north as Bolivia, Paraguay, and southern Brazil. The exposure from where the material was collected represents a rich parautochtonous assemblage — also including marine taxa — that has been assigned to the Late Miocene. Extant representatives of Polymesoda and Erodona are known to inhabit mostly brackish environments in the Caribbean region, the eastern Pacific coast of America, and Southeast Asia (in the case of Polymesoda), and the Atlantic coast of southern South America (Erodona). The presence of these bivalves in the Paraná Formation suggests that at least a marginal connection may have existed between a southern arm of the Amazonian Sea and the Paraná Sea during the Miocene. It is highly unlikely that these taxa could have migrated along the Atlantic coast of South America — contrarily to the case of the fully marine taxa — in view of their peculiar ecological requirements.

We examine variation in species richness, species composition and distance decay in similarity in forest snail faunas from Poland and a small part of Transcarpathian Ukraine, and their connection with geographical position in relation to Pleistocene refugia. Forest faunas were sampled from sites of standard size in each of ten regions. Data were analysed using DCA and partial CCA, extracting the geographical, climatic and ecological correlates with the major axes. Relationships among site and regional faunas were further examined through the Simpson Index of Similarity. Site species richness shows no significant variation with geographical position or climate, but relates to soil and vegetation characteristics. Composition varies with location; southern highland faunas differ from one another far more than do northern lowland faunas, showing a clear east-to-west pattern of change. The aggregate highland fauna is richer than that of the lowlands, which is a subset of the former. Two intermediate upland regions show different associations, one with the highlands the other with the lowlands. Lowland faunas, even over large distances, are very similar, and all relate more closely to the western end of the highlands than to the east. Disaggregating the fauna into large and small species shows that the former show a stronger geographical pattern than the latter; most universally distributed species are small. Latitudinal variation in regional richness, and longitudinal differentiation among highland faunas relate to distance from glacial refugia. This is not reflected in site species richness, raising questions about the assembly rules for local faunas. The western bias in the relationships of lowland faunas to those of the highlands, the differences between large and small species and the varying rates of faunal turnover within the area studied suggest that patterns of post-glacial dispersal are complex and incompletely understood.

Two introduced predatory land snails, Euglandina rosea and Oxychilus alliarius, have been implicated in the decline of native Hawaiian and Pacific island land snails. We examined the feeding ecology of E. rosea and O. alliarius, focusing first on prey size and species preferences, and second on quantifying consumption rates, which is necessary to address the possible levels of impact on natural populations. In prey-size preference experiments, E. rosea always consumed more snails in the smaller size class. In prey-species preference experiments, E. rosea preferred snails to slugs but showed no preference among snail species. Size preference experiments indicated that O. alliarius will only consume prey less than 3 mm in shell length. In prey species preference experiments O. alliarius consumed every snail species offered but did not consume either of the slug species. Consumption rates were positively related to the size of the predator, with the larger predator, E. rosea, having a much higher consumption rate than O. alliarius, and with larger E. rosea consuming more than smaller E. rosea. These results have unfortunate conservation ramifications, because since they indicate that both E. rosea and O. alliarius are generalist snail predators feeding preferentially on the smallest snails, although they rarely eat slugs. Since many extant Hawaiian and Pacific island snail species are small, they are at risk of predation by these two introduced predators, while invasive slugs — there are no native slugs in Hawaii — may not be impacted by them.