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Omalonyx unguis was previously known to occur in Argentina, Paraguay and Uruguay. We report the first conclusive record of occurrence of this species in Brazil, based on specimens collected in three localities in the Paraguay River sub-basin (Mato Grosso do Sul state – Campo Grande and Miranda; Mato Grosso state – Poconé), and in the Brazilian margin of the Paraná River (Foz do Iguaçu, Paraná State). The species was identified by comparative morphology of the reproductive system, and a map that synthesizes the literature and reports new records is presented.

The genus Omalonyx d'Orbigny, 1837, includes neotropical semi‐aquatic succineid slugs and comprises six recognized species to date. Field surveys across continental South America recovered five of the six recognized species. According to the morphological characters traditionally included in Omalonyx descriptions, the specimens were tentatively identified as O. matheroni, O. pattersonae, O. convexus, O. geayi and O. unguis. Employing sequences of mitochondrial cytochrome oxidase I (COI) alone or combined with the nuclear second internal transcribed spacer (ITS2) in discovery methods of species delimitation (GMYC and STACEY) led to species delimitation hypotheses that, except for unambiguously supporting O. convexus, have no correspondence to morphologically based assignments. To choose the delimitation model that best fit our data, the hypotheses recovered by GMYC, STACEY and morphology and created by merging species recovered by those methods had their marginal likelihood estimated and compared using the Bayes factors. The best‐supported hypothesis distinguished two species besides O. convexus: one widespread over most of South America and the other restricted to Rio de Janeiro State, Brazil. Furthermore, the pattern of genetic structuring supports pathways connecting the Amazonian and Atlantic forests. This pattern is similar to that observed in terrestrial taxa (e.g., forest‐dwelling small mammals) and is different from the pattern for fully aquatic taxa.

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Accurate distributional information is crucial for studies on systematics, biodiversity and conservation. To improve the knowledge regarding the geographical distribution of Omalonyx in South America, we present updated information based on data from a literature review, institutional collections and malacological surveys. All this information composed the dataset used to predict species distribution employing the Maximum Entropy Algorithm (MaxEnt). The model was run using data on species distribution, altitude and bioclimatic variables (WorldClim database). The model had consistent performance, and areas presenting similar conditions to areas where the species were recorded were considered areas of occurrence. The predicted occurrence areas included those that were already surveyed and those that are considered potential occurrence areas. The results demonstrate that the genus has widespread distribution in the Neotropical region and occurs in the tropical, temperate and arid regions of South America and Lesser Antilles. Omalonyx spp. were recorded in all South American countries and hydrographic regions. However, in some countries, there were only isolated records (ex: Colombia and Ecuador). Here, we also present the first record of Omalonyx spp. in four Brazilian States (Acre, Rondônia, Piaui, and Amapá). The genus was found in all hydrographic regions within Brazil and among 27 federative unities; it was absent from only two unities (Roraima State and Distrito Federal). This work contributes to the knowledge on Omalonyx spp. distribution and provides an important basis for the work of ecologists and taxonomists.

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The use of molecular tools in Brazilian malacological studies was analyzed. We searched for these molecular tools by screening the annals of malacological events in Brazil and Latin America within the last 15 years. Information was obtained from a Brazilian curricula data bank (curriculum Lattes), which enabled the identification of the main national research groups, their main researchers and research focuses. An estimate of the scientific production on the basis of the analysis of these curricula is also provided. The main techniques and molecular markers employed were indicated. The data showed that these studies were concentrated in institutions in the South and Southeast regions and emphasized gastropods of medical importance. However, molecular studies that examined other gastropods, cephalopods and bivalves were also performed. No research study was found in the Central-West region of the country. The growth of this field of study in the country is expected, considering the molecular studies that have been performed and the great diversity of the molluscan fauna in Brazil. Future molecular studies on some taxa in the country, which have not yet been studied, should be contemplated. The increase in the use of sequencing techniques will help to bridge the gaps in our taxonomic and phylogenetic knowledge, contributing to the studies on biodiversity and conservation. Keywords: Molecular biology, malacology, snail, Brazil, DNA.

Despite the epidemiological importance of the Lymnaeidae family regarding transmission of Fasciola hepatica, knowledge about the diversity and distribution of these molluscs and the role of each species in the expansion of fasciolosis remains sparse. Classical morphological (n=10) identification was performed in lymneids from Lagoa Santa, a municipality in the state of Minas Gerais, Brazil, along with molecular and phylogenetic analysis (n=05) based on the partial nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I gene (COI mtDNA) and ribosomal internal transcribed spacer II (ITS-2 rDNA). The shell morphology made it possible to distinguish the lymneids of Lagoa Santa from Pseudosuccinea columella. Differences found in the penile complex and prostate shape allowed this species to be distinguished from Galba truncatula. However, the homogeneity of reproductive tract characteristics among Lymnaea (Galba) cubensis, L. viator and L. neotropica confirmed that these characteristics show low taxonomic reliability for identifying cryptic species. Genetic divergence analysis for the COI mtDNA gene and ITS-2 region of rDNA revealed greater similarity to Lymnaea (Galba) cubensis. Thus, correct species differentiation is important for monitoring the epidemiological risk of fasciolosis in the state of Minas Gerais, where cases of the disease have increased over recent years.