Plagiodontes dentatus (Wood, 1828) is the type species of a South American genus including eight named species that show a high degree of local endemism. Due to some misidentifications with P. multiplicatus (Doering, 1874) and P. daedaleus (Deshayes, 1851), P. dentatus has been cited as inhabiting two disjunct areas with quite different ecological conditions. In this paper the identity of this morphospecies is clarified through a study of shell sculpture and apertural teeth data, and a comparison with the smaller adult specimens (<25 mm long) of its closest species, P. patagonicus (d’Orbigny, 1835) and P. multiplicatus, i.e., the only shells to which P. dentatus could have been confounded. A statistical analysis of shell variability revealed that, beyond the qualitative diagnostic characters, there are significantly different shell proportions that also define P. dentatus. The distribution of P. dentatus over two disjunct areas is not supported, its confirmed geographic range being restricted to the Oriental Republic of Uruguay and the Argentine provinces of Entre Ríos and northeastern Buenos Aires. An intraspecific multivariate analysis upholds the opinion that any subspecific discrimination is unwarranted.

Temperature can be a limiting factor on parasite development. Riccardoella limacum, a haematophagous mite, lives in the mantle cavity of helicid land snails. The prevalence of infection by R. limacum in populations of the land snail Arianta arbustorum is highly variable (0-78%) in Switzerland. However, parasitic mites do not occur in host populations at altitudes of 1290 m or higher. It has been hypothesized that the host's hibernation period might be too long at high elevations for mites and their eggs to survive. To test this hypothesis, we experimentally infected snails and allowed them to hibernate at 4°C for periods of 4-7 months. Winter survival of host snails was negatively affected by R. limacum. The intensity of mite infection decreased with increasing hibernation duration. Another experiment with shorter recording intervals revealed that mites do not leave the host when it buries in the soil at the beginning of hibernation. The number of mites decreased after 24 days of hibernation, whereas the number of eggs attached to the lung tissue remained constant throughout hibernation. Thus, R. limacum survives the winter in the egg stage in the host. Low temperature at high altitudes may limit the occurrence of R. limacum.

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Plagiodontes patagonicus (d'Orbigny, 1835) is a quite variable species endemic to southern Buenos Aires province (Argentina). Its taxonomic characterization did not include any quantitative analysis of variability for an accurate discrimination, and the extremes of its variation were described as different subspecies or species. In this paper, shell measurements and angles, and quantitative data on the terminal male genitalia were studied by Principal Component Analysis and Varimax multivariate analysis. Typical Plagiodontes patagonicus and the largest form known as P. patagonicus magnus Hylton-Scott, 1951 showed an almost continuous pattern of shell variation, which is positively correlated with the altitude gradient over their geographical range, which in turn is correlated with a rainfall gradient, i.e. they constitute a size-form cline that does not allow objective delimitation of different morphospecies. Data from the genital system were also arranged as a geographical gradient within the P. patagonicus patagonicus-P. patagonicus magnus continuum. The variability of protoconch sculpture and apertural teeth also indicate recognition of them as a single taxon.

Plagiodontes weyrauchi sp. nov. is among the smallest species in the genus Plagiodontes (Doering, 1877). Statistical multivariate analyses confirmed its distinctiveness from other species, mostly because of its high number of whorls (8-9.75), relatively small width, and low proportions of last whorl and aperture length to shell length; multivariate discriminant analysis applied to this species and its most similar relative, P. multiplicatus parvus, correctly identified 100% of specimens. Pallial and genital anatomy supports P. weyrauchi as a different species, mainly because of the position of the ureteric pore, the small general size of the genital system, the presence of an accessory lobe alongside the verge, and the vaginal internal structure. Internal anatomy of four other small-sized taxa in the genus was studied. Two of them have a verge with no accessory lobe [P. dentatus (Wood, 1828) and P. patagonicus (d'Orbigny, 1835)], while the remaining two have an accessory lobe with different characteristics [P. rocae Doering, 1881 and P. multiplicatus parvus (Hylton-Scott, 1952)]. Internal structure of the vagina also shows specific differences among Plagiodontes species; their phylogenetic significance will be further investigated.

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Background: Sperm size and quality are key factors for fertilization success. There is increasing empirical evidence demonstrating that sperm form and function are influenced by selective pressures. Theoretical models predict that sperm competition could favour the evolution of longer sperm. In hermaphrodites, self-fertilizing species are expected to have shorter sperm than cross-fertilizing species, which use sperm stored from several mating partners for the fertilization of their eggs and thus are exposed to intense sperm competition. We tested this hypothesis by comparing original data on sperm length in 57 species of simultaneously hermaphroditic stylommatophoran gastropods from Europe and South America with respect to the species' breeding system. We used 28S rRNA nuclear and COI mitochondrial sequence data to construct a molecular phylogeny. Phylogenetic generalized linear models were applied to examine the potential influence of morphological and life-history characters. Results: The best-fit model revealed that the breeding system and age at sexual maturity influence sperm length in gastropods. In general, species with predominant cross-fertilization had longer sperm than species with predominant self-fertilization or a mixed breeding system. Across species with shells (snails), sperm length also increased with shell size. Conclusions: Our study provides evidence that sperm length in stylommatophoran gastropods is influenced by the risk of sperm competition, as well as by age at sexual maturity and shell size. This finding extends present knowledge of sperm evolution to a group of so far poorly studied simultaneous hermaphrodites.

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