This study aims at updating the diversity and distribution of Sphaeriidae in Argentine Patagonia, with a particular emphasis on the Santa Cruz Province. Samples were collected between 2015 and 2023 across diverse habitats, including rivers, lakes, lagoons, and Patagonian wetlands, and this was complemented by data obtained from a comprehensive literature review and a revision and improvement of major malacological collections. Both manual and sieve-based collection methods were used to obtain specimens from different habitats. From 121 records analyzed, 101 records were identified to species level, including four species of Pisidium and two of Sphaerium. Pisidium magellanicum and Pisidium patagonicum were the most frequently recorded species. Sphaerium patagonicum demonstrated the broadest distribution, ranging from northern Neuqu & eacute;n to southern Tierra del Fuego. Santa Cruz Province had the highest number of records (57), followed by Chubut (24), with R & iacute;o Negro and Tierra del Fuego having the fewest records. We report the first record of Pisidium chilense in Neuqu & eacute;n Province, providing new evidence of its presence in Argentine Patagonia. These findings advance our knowledge of Sphaeriidae distribution in Patagonia and highlight gaps in coverage, particularly in less-sampled regions.

AbstractNudibranchs of the genus Spurilla (Aeolidiidae) are currently represented worldwide by five species: S. braziliana, S. croisicensis, S. dupontae, S. neapolitana, and S. sargassicola. Two of these, S. neapolitana and S. braziliana, have been previously reported from the Argentine Sea. This study aimed to identify Spurilla specimens collected from intertidal zones at four sites in the San Matías Gulf. We conducted detailed morphological and anatomical examinations, including external traits (body coloration, rhinophores, and cerata) and internal structures (radula, jaws, nervous system, and reproductive system). These characteristics were compared with published descriptions of all five known species. To strengthen our findings, we incorporated a molecular approach based on mitochondrial gene sequences. The analysis revealed low genetic differentiation between populations from Argentina and Brazil, supporting the presence of a single, widespread species, S. braziliana, throughout the southwestern Atlantic. Genetic patterns also suggest that Brazil may represent the species' center of origin, with subsequent southward dispersal to Argentina and northward expansion toward Central America and the Caribbean. This revision confirms that S. braziliana is the only species of the genus present along the western coast of the San Matías Gulf, contributing to a clearer understanding of regional marine biodiversity and species distributions.

Invasive species require long-term characterization of their shifting population dynamics to understand their environmental impacts and socio-economic effects. The dynamics of freshwater bivalves depend on their biology, which is influenced by the vulnerability of the ecosystems. This study evaluates the coexistence of Corbicula fluminea and C. largillierti in a stream in the Argentine Pampa, integrating density, size, and reproduction. In this stream, characterized by a temperate climate and hydrological fluctuations, live specimens of both species were sampled monthly using a 0.07 m2 cylinder. The anteroposterior length of each specimen was measured, and size distributions were analyzed by decomposing normal modes using the least-squares method. Gonadal cycles were compared with data from the previous literature. Since 2004, C. fluminea has dominated the system with significantly higher densities. Both species exhibited contrasting reproductive cycles. Hydrological instability in the stream limited both species. C. fluminea dominated due to its greater resilience and longevity under stress. In contrast, C. largillierti prioritized initial rapid growth, making it more sensitive to fluctuations. These results highlight that environmental instability conditions invasive success and interspecific competition in freshwater systems.

Global awareness of introduced species as one of the primary drivers of biodiversity change—causing environmental impacts, and economic and social effects—emphasizes the need to enhance our understanding of these species. Developing a comprehensive database will enable policymakers to identify global bioinvasion patterns and strengthen their capacity to manage them effectively. Aquatic mollusks play a crucial role in the ecosystems they inhabit, influencing food webs and nutrient cycling, and habitat formation and modification. They are also the dominant group in aquaculture, contributing significantly to the economy while also causing economic losses through macrofouling and posing health risks. Despite their importance, information on the introduction, establishment, and dispersal of mollusk species in South America remains scarce and is often confined to the grey literature. With the aim of organizing, increasing, and strengthening the knowledge of non-native and transplanted mollusks in general and aquatic mollusks in particular, 29 specialists in the introduced mollusks of South America, from seven countries, have been working collaboratively since 2016. Each member contributes expertise, data, and bibliographic resources to build the status of the introduced mollusks in South America and provide critical information to prevent future introductions and transplants. In aquatic environments, 41 non-native mollusk species and 18 transplanted species have been identified. Among them, the bivalve Limnoperna fortunei stands out with the greatest economic effect, while the gastropods Lymnaeidae and Thiaridae represent significant health concerns. Although this research represents a major step forward, it also highlights challenges such as the scarcity of taxonomic studies and the limited investigation of vast areas in South America. The information compiled in this review serves as a resource for researchers, policymakers, and the general public when addressing mollusk bioinvasions in South America.

Ecosystems and biodiversity around the globe face multiple threats, including climate change and invasive species. Non-native species are known for their resilience to disturbances and their ability to thrive more successfully than native species in urbanized or otherwise disturbed areas, and some of them can become invasive. It is a complex challenge to detect, manage, and control such species, which require coordinated efforts from society, government, and the academic community. In this study, the eMIAS (South American Invasive Mollusks Specialists) research group (27 experts from seven South American countries) aim to provide foundational knowledge for management of these species. We compiled and synthesized information on the mollusc species that are native to South America and that have been introduced to other regions of the world. A total of 29 species were detected, including 10 marine, 10 freshwater, and 9 terrestrial. For each species, the area of origin, date and place of introduction, and current distribution were determined. We could determine that (1) most of these introductions have occurred in connection with globalization processes, such as an increase in trade. (2) The potential source regions of those 29 species are also areas that received non-native species from elsewhere (e.g., Europe, Asia). (3) Regions where species introductions have taken place are subject to the impacts of climate change and/or urbanization.

Globally, the Unionida have suffered an increasing decline in both their populations and distribution range. This phenomenon has been well documented in Europe and North America. In Argentina, the study of the group reached its height between 1960 and 1980, producing valuable but now outdated information. This study aims to explore the distribution range before and after 1990 and discuss the potential threats to Unionida (Hyriidae and Mycetopodidae families) in Argentina. We analyzed bibliographies, databases, and new samplings following the malacological provinces of Argentina (MP) zoogeographic scheme. A total of 2452 georeference records were analyzed. Of the 35 species detected up to 1990, 17 (48%) have not been recorded since that year. Freshwater mussels are recorded in seven of the eight MP and in six there has been a reduction of more than 50%. Climate change (increasing water temperature, droughts or extreme floods, and fires), globalization (invasive species), and human activity (intensive agriculture, wastewater discharge, construction of dams or river channelization, and commercial exploitation) have all contributed to the decline and reduction of native mussel populations, leading to range reduction and extirpation. The results of the present study will allow future research to estimate the endangered status and degree of conservation of unionidan species in southern South America, which provide multiple ecosystem services.

Invasive non-native freshwater mollusks are a growing concern in South America, with 16 species already recorded in the region. Among them, Sinotaia quadrata has only been documented in Argentina, for the first time in the Punilla Valley, Córdoba (2009) and La Plata, Buenos Aires (since 2015). In this study, we report the presence of S. quadrata in two additional areas, the Río de la Plata River and a stream (unnamed) in the Paraná River basin, two of the most significant rivers in South America, located in the provinces of Buenos Aires and Entre Ríos, respectively. These new records confirm the invasive nature of this species, which has also been identified in Europe, the United States, and Africa in recent years. The findings of this study highlight the need for continued monitoring and management of invasive species in South America's freshwater ecosystems.

Invasive non -native freshwater mollusks are a growing concern in South America, with 16 species already recorded in the region. Among them, Sinotaia quadrata has only been documented in Argentina, for the first time in the Punilla Valley, C & oacute;rdoba (2009) and La Plata, Buenos Aires (since 2015). In this study, we report the presence of S. quadrata in two additional areas, the R & iacute;o de la Plata River and a stream (unnamed) in the Paran & aacute; River basin, two of the most significant rivers in South America, located in the provinces of Buenos Aires and Entre R & iacute;os, respectively. These new records confirm the invasive nature of this species, which has also been identified in Europe, the United States, and Africa in recent years. The findings of this study highlight the need for continued monitoring and management of invasive species in South Americ & aacute;s freshwater ecosystems.

Physa acuta is a freshwater snail of North American origin that has spread to all continents. In South America it was detected for the first time in 1966 (Brazil) and is currently present in Argentina, Brazil, Peru, Chile, Colombia, Ecuador and Uruguay, occupying 13 of the 52 South American freshwater eco-regions. Its introduction would be related to the import and transportation of aquatic plants. Here we update the distribution of P. acuta in Argentina based on a review of scientific collections, published works and new collections. Our review expands the distribution of the species from 11/23 Argentine provinces (until 2010) to 19/23, and we report the first record for the province of Santa Cruz, this being the southernmost site of the species. This new discovery in the province of Santa Cruz (Austral Patagonia), with an established and reproducing population in an urban area, poses a potential threat to local biodiversity (where there are no records of other non-native mollusks) and to human and animal health. This is due to the finding of populations in southern Argentina that are naturally infested by Fasciola hepatica. The record of P. acuta in aquatic environments of southern Patagonia makes it necessary to generate monitoring and control plans with the objective of identifying the dispersion vectors and preventing the spread of the species in other water bodies in the region.

Invasive non-native freshwater mollusks are a growing concern in South America, with 16 species already recorded in the region. Among them, Sinotaia quadrata has only been documented in Argentina, for the first time in the Punilla Valley, Córdoba (2009) and La Plata, Buenos Aires (since 2015). In this study, we report the presence of S. quadrata in two additional areas, the Río de la Plata River and a stream (unnamed) in the Paraná River basin, two of the most significant rivers in South America, located in the provinces of Buenos Aires and Entre Ríos, respectively. These new records confirm the invasive nature of this species, which has also been identified in Europe, the United States, and Africa in recent years. The findings of this study highlight the need for continued monitoring and management of invasive species in South America's freshwater ecosystems.

The Natural Reserve of Punta Lara (RNPL) is a protected natural area that includes Paranaense forest southernmost in the world. This area is surrounded by a densely populated and touristic sector. The objective of this work was to estimate the richness, diversity and equity of the RNPL mollusks (aquatic and terrestrial) and to establish the relationship of their species in aquatic environments. One sampling per year was carried out between 2013 and 2019. There were 32 species recorded (six are non-native species): 23 gastropods (14 freshwater, nine terrestrial) and nine bivalves. Three species were recorded in all sampling years, while six only on one occasion. The land snail genus Drepanostomella is reported for the first time in that region, and five freshwater species are reported for the first time for the RNPL. The similarity analysis of the freshwater environment separated the coastal environments from the internal environments. The environments with the highest specific richness were in internal sites of the RNPL, while the least diverse was the coast of the Río de la Plata, where the invasive species Limnoperna fortunei predominates. It is recommended to increase the conservation efforts of the different environments of the RNPL continuously threatened by urbanization.

The impacts of biological invasions remain poorly known for some habitats, regions and taxa. To date, there has been no comprehensive effort to review and synthesize the impacts of invasive mollusc species in South America. In this paper, we provide a synoptic view on what is known on documented socio-ecological impacts of aquatic no-native mollusc species (NNMS) and transplanted mollusc species (TMS) from South America. An expert group involving malacologists and taxonomists from different countries, the “South America Alien Molluscs Specialists” (eMIAS), shared and summarized the scientific literature, databases, and published and unpublished information on confirmed impacts of NNMS and TMS in South America. Three broad categories, non-mutually exclusive were used as a framework: “Environmental/Biodiversity impacts”, “Economic and social effects”, and “Human health impacts”. Some 21 NNMS and seven TMS have documented impacts on at least one of those three categories. We encourage targeting the less known areas of research, such as economic valuation of human health (and veterinary) impacts attributable to NNMS or TMS and expand our knowledge of environmental impacts for the species listed in this study.

Limnoperna fortunei, a problematic freshwater invasive mussel in South America, was first detected in 1991 at Bagliardi Beach, Río de la Plata (Argentina). Since then, there has been a high increase in population density, reaching up to 150,000 ind. m−2. The distribution, density, individual sizes, and associated mollusk assemblages of L. fortunei were evaluated 30 years after its first detection. Seven sites along Río de la Plata River were sampled between 2018 and 2020. The highest density was recorded in the La Balandra Beach (above the stabilization value) and the lowest density in the Martín García Island (IMG—by its acronym in Spanish—, below the stabilization value). Two reproductive events were observed: late spring and late summer. Our results showed different sets of species associated with Limnoperna fortunei, with protected areas such as the IMG standing out, showing greater species richness, including first records, versus other coastal environments. We recommend increasing conservation efforts given the constant advance of urbanization in the coastal sites of the province of Buenos Aires, with environmental impact studies prior to coastal reforms, and implementation of density control strategies for Limnoperna fortunei in protected areas.

The movement of species is among the most serious environmental threats of the new millennium, as the transplantation of species beyond their native or historical range has intensified in the last five decades. Traditionally, studies on bioinvasions have focused on species that have been introduced, deliberately or accidentally, to biogeographic regions where they did not previously occur. However, less attention has been given to species movement to novel areas within the same biogeographic region. Our research group, the South America Introduced Molluscs Specialists, analyzed potential cases of native South American mollusc species introduced deliberately or accidentally beyond their natural range within South America. To achieve this, it is key to differentiate between anthropogenic processes and passive responses to environmental conditions. We considered the past and current spatial distribution of species, analyzed known or putative vectors, and discuss the impacts of taxonomic and nomenclatural knowledge. Based on the evidence currently available, we propose different scenarios to explain observed changes in mollusc distributions within South America. Seventeen transplanted mollusc species (TMS) were recognized, considering marine, freshwater, and terrestrial environments. Of the 189 South American ecoregions 31 were occupied by transplanted species, but this proportion varied by environment: 10 of 28 marine ecoregions, 12 of 52 freshwater ecoregions, and 9 of 109 terrestrial ecoregions. The ecoregions with TMS are generally located in the peripheral zones of the continent. Those with the highest number of TMS were the Southern Caribbean (three species) in the marine environment, the Central Andean Pacific Slopes (three species) in the freshwater environment, and the Alto Paraná Atlantic forests (two species) in the terrestrial environment. The number of unintentionally moved TMS is greater than those moved intentionally. The transplantation process is similar to the introduction and settlement process of non-native mollusc species, and so is their impact.

ABSTRACT Heterobranch sea slugs exhibit a wide range of body shapes, sizes and color patterns. The genus Placida (Sacoglossa) includes cryptic species, and in 2019 four species were recovered through molecular studies. Specimens of Placida collected in the Argentinian Sea (San Matias Gulf, Patagonia) between 2016 and 2019 are shown to belong to an undescribed species using molecular and morphological evidence. Placida sudamericana n. sp. is described using external, radular, penial stylet and egg mass characters. The specimens were always found associated with the green algae Codium fragile. Placida sudamericana is the only Placida species in the South Atlantic waters of South America and was recorded in a molluscan biodiversity hotspot.

The Atlantic Forest is a highly fragmented biodiversity hotspot, which in Argentina is represented by the Paranaense Forest, covering a wide area of the province of Misiones. In conservation studies, groups of vertebrates, plants and arthropods are generally used together but other invertebrates scarcely used. In the present work, we aim to provide information on new species of freshwater gastropods, from protected and unprotected areas. Specimens were collected in a protected area (Yabotí Biosphere Reserve) and in two unprotected areas (Alba Posse city and Centro de Investigaciones Antonia Ramos -CIAR-). The shell, radula, internal anatomy and the molecular information of the partial sequence of mitochondrial cytochrome c oxidase subunit I (COI) were analysed. The phylogenetic trees were obtained using Maximum Likelihood and Bayesian Inference analyses. Altogether, the anatomical, shell, and genetic studies allow us to differentiate six new species of the genus Potamolithus from the others present in Argentina and the surrounding areas. These new species raise the number of freshwater gastropods for the malacological province Río Uruguay to 64. Three of the new species have been found within a protected area, while other three at unprotected areas. The presence of invasive species, such as Limnoperna fortunei (Dunker 1857) and Melanoides tuberculata (Müller, 1774), as well as the possible creation of a hydroelectric dam, may modify the environment inhabited by the new endemic fauna.

Twenty-five sub-ecoregions make Argentina from southern South America a favored area to study the mutual correspondence between environments and biodiversity. Unfortunately, efforts devoted to study these environments are unbalanced, with the subtropical dry forests less studied than the tropical and subtropical humid ones. Since the limits of ecoregions are based on vegetation criteria, land gastropods represent an independent source of information to test the relevance of sub-ecoregions in different aspects of biodiversity. We ask if land gastropods mirror these traditional diversity patterns when their distributions are framed in the context of sub-ecoregions. Additionally, we want to test if short-range endemic species (SRE) are randomly scattered across the sub-ecoregions. We first built an updated taxonomic checklist and mapped all the valid records compiled to date. Taxonomic richness, taxonomic diversity, and beta-diversity between sub-ecoregions were calculated. We obtained a hierarchical grouping of sub-ecoregions and the respective list of species that significantly support each cluster. We also developed two new analytical resources: a radial plot for showing the species composition of clusters resolved at three taxonomic levels, and a mixed coefficient of distributional size useful to identify SRE from sparse point records. This dimensionless measure of spatial range combines information of both the convex hull area and the length of the minimum spanning tree connecting point localities of presence. The Southern Andean Yungas and Dry Chaco are the species-level richest ecoregions. Although the Paranaense Forest harbors half of the number of species found in the Chaco Serrano, it reaches the highest score of taxonomic diversity because of the eclectic nature of their genera. SRE species are not randomly distributed across the sub-ecoregions, but they broadly overlap with the orographic Peripampasic arc extended over Chaco Serrano and Yungas Forests. SREs are highly dependent on the physical nature of the landscape.