In contrast to their relative ecological and economic importance, many species of Ampullariidae remain poorly studied, and lack robust data needed to clearly circumscribe the species or understand their biogeographic distributions. A few, e.g., Pomacea maculata Perry, 1810 and P. canaliculata (Lamarck, 1822), have been well studied, in part because of their notorious reputations as invasive pests. Unfortunately, beyond broad phylogenetic studies, we know little about the relationships and distributions of the dozen or so other species with which these two well-known ampullariids have and continue to be confused. The ability to delimit such species not only has implications for invasion biology, but also for conservation of native species. The ampullariid Pomacea sordida (Swainson, 1823) is endemic to the state of Rio de Janeiro, Brazil. Recent molecular analyses revealed that several populations previously referred to as P. sordida, belong to another genetically distinct species, Pomacea intermedia (Férussac in Quoy & Gaimard, 1825), currently regarded as a junior synonym of P. sordida. To evaluate the validity of this previous study, we examined all of the material identified as P. sordida from the collection of the Institute Oswaldo Cruz and carried out additional surveys across the known distribution of these species. Phylogenetic analyses of COI sequences from 96 snails sequenced for this study, along with additional sequences from GenBank, recovered P. sordida and P. intermedia as sister taxa in a clade sister to P. flagellata (Say, 1829) and P. patula (Reeve, 1856). Surveys of aquatic habitats in the state of Rio de Janeiro recovered both species in allopatric populations with P. sordida primarily restricted to seven sites in the southwestern part of the state, whereas P. intermedia occurred in six sites in the central part of the state, northeast of P. sordida populations. Although cursory examination of male reproductive anatomy of these two species does not provide taxonomically informative characters that allow delineation of these two species, other traits e.g., juvenile shell characters, egg morphology, and kidney shape and arrangement, appear to be informative and provided necessary data to rescue P. intermedia from synonymy with P. sordida.

Many freshwater snail species of the family Lymnaeidae are known to act as intermediate hosts of Fasciola hepatica, the causative agent of fasciolosis, a parasitic disease of great veterinary and medical importance. Morphological identification of lymnaeid species is based on characteristics of shell, reproductive and renal systems. However, such identification is challenging due to interspecific similarity, which is particularly evident among the species Galba viator, G. cubensis, and G. truncatula. To overcome these difficulties, we used molecular markers and a morphological approach applied to specimens from Brazil to compare the data obtained with type specimens, topotypes, and other lymnaeid species. We used PCR-RFLP with MboII, HpaII, and AluI enzymes directed to the ITS2-rDNA region, which allowed differentiation among Pseudosuccinea columella, Pectinidens diaphanus, G. viator, G. cubensis, and G. truncatula when morphological characterization is inconclusive. These results allowed us to report for the first time the occurrence of G. cubensis and G. truncatula in the state of Minas Gerais, Brazil. We also performed phylogenetic analyses using 16S mtDNA sequences, which corroborated the PCR-RFLP results. The molecular techniques used in this study aimed to support the morphological identification of Lymnaeidae populations from Brazil and have proven to be a helpful tool when morphological analysis does not support confident identification at the species level.

Lepidochitona is a genus with a wide distribution in the Atlantic and Pacific oceans. In this study, we describe Lepidochitona pardogandarillasae new species using morphological and molecular data. This new species is morphologically distinct from other species of the genus in displaying a convex postmucronal slope, the jugal part of tegmentum slightly protruded, and a large body length (> 20 mm). The phylogenetic analyses conducted in this study using mitochondrial markers confirm the existence of a new species of Lepidochitona, which was found in northern Peru. This study represents a contribution to knowledge of the Lepidochitona diversity and distribution along the eastern Pacific.

The study of diet and how a species obtains food is relevant to understand its role within natural environments. The apple snail Pomacea canaliculata (Lamarck, 1822) is a freshwater dweller that primarily consumes aquatic macrophytes and detritus but also incorporates resources of animal origin in its diet. Our aim was to investigate the ingestion of macroinvertebrates by P. canaliculata in four watercourses from its native range by analyzing its digestive contents. The frequency of occurrence of animal remains in the digestive contents of P. canaliculata snails was 68.50% across different seasons, with values of more than 50% in each of the watercourses studied. The spring-summer contents showed high frequencies of animal remains, whereas in autumn they were recorded only in 10% of the contents from one of the watercourses. The macroinvertebrates ingested belonged to six different insect orders, crustaceans, mites, bivalves, and gastropods. The frequencies of occurrence were higher for arthropods than for mollusks in two watercourses and similar in the other two. In two watercourses, the relative abundances of mollusks were higher than those of arthropods and the opposite was true in the other two. The number of individuals ingested by an average P. canaliculata was highest for the snail Heleobia parchappii, followed by arthropods, H. parchappii eggs, and the snails Physella acuta and Chilina parchappii. Most ingested macroinvertebrates were small, slow or with little or no mobility, such as snails and case-bearing insects. Arthropods able to swim or to swiftly escape, such as Amphipoda and nymphs of Odonata and Ephemeroptera, were not detected at all in the digestive contents. Ingestion of macroinvertebrates appears to be opportunistic and even accidental and probably depends more on their microhabitats or behavior than on preferences of P. canaliculata. Notwithstanding, the high frequency of ingestion observed on some species of snails could have a significant negative effect on the abundance of their populations.

Aneuploidy, or presence of an abnormal number of chromosomes, has been commonly observed in marine bivalves. This phenomenon has also been shown to be negatively correlated with growth and survival rates in several species of oysters and clams. The impact of pollutants on the aneuploidy level in bivalves has also been previously demonstrated. Over the past two decades, evidence of nonrandom chromosomal loss has been demonstrated, with the identification of the missing chromosomes in aneuploid karyotypes reported in several species. The results have shown that only a few pairs were preferentially affected by the loss of one homologue chromosome in different species of oysters and clams. Recently, during the genotoxicity assessment of the marine environment in Qatar using the pearl oyster Pinctada radiata (Leach, 1814) as model and surrogate species, we observed hypodiploid and hyperdiploid karyotypes. Hyperdiploidy was more frequent, which is highly uncommon in bivalves. The identification of the extra and missing chromosomes in aneuploid cells showed that pairs 4, 5, 12, and 13 were found to be more susceptible than others in having an extra individual chromosome. The same set of pairs showed a tendency to lose one homologue chromosome. Several hypotheses on the preferential chromosomal susceptibility in bivalves, in general, are discussed.

Exotic species that achieve successful invasions often show considerable dietary plasticity in resource choice, sometimes adjusting their diet to new or variable resources. This can increase species' impact in the recipient environment. In this study, we explore the diet of the invasive gray side-gilled sea slug Pleurobranchaea maculata (Quoy & Gaimard, 1832) in two environments with contrasting presence of algae (different depths) on northern Patagonian coasts, by means of stable isotope analysis. Results showed the most probable prey contribution to the diet of shallow individuals of P. maculata to be algae, whereas colonial tunicates were the preferred prey in deep environments. Therefore, we suggest that P. maculata behaves as an omnivorous species in the receiving community, because it consumes and assimilates the algae, which represents a dietary shift compared to their original feeding habits (carnivorous). This species exhibited the ability to adapt to different dietary resources by showing significant differences in niche locations, niche breadth, and exhibiting little to no overlap between different environments, which supports the previous description of P. maculata as a generalist consumer. Pleurobranchaea maculata's dietary plasticity might drive ecological consequences in the invaded community. Thus, it is important to monitor for future changes in the benthic community to develop efficient programs for the management of this invasive voracious species.

A common issue for several freshwater snail families is the fact that, for some genera, the criteria for species delimitation are scarce, subjected to intraspecific and ontogenetic variation, or insufficiently discrete to allow a clear distinction between species. For these genera, the use of molecular approaches is decisive in recognizing valid species. Herein, we applied coalescent methods to delimit evolutionary significant units (ESUs) in Physidae. We used 496 sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene available in GenBank, ascribed to six genera and 25 nominal species, and the algorithms GMYC (General Mixed Yule-Coalescent) with two criteria (single-threshold and multiple-threshold), PTP (Poisson Tree Process), and mPTP (multi-rate Tree Poisson Process). The method that presented the best performance was the mPTP. This method showed a higher frequency of taxonomic species recovery and has delimited a lower number of ESUs (25 ESUs from a dataset attributed to 25 nominal species). Physidae is a family of freshwater snails that presents several issues related to the recognition of species boundaries. Herein, the use of coalescent delimitation methods allowed us to address important taxonomic questions, opening new avenues for future taxonomic research. Our findings have shown that the morphological operational criteria used to delimit several valid species fall within the limits of intraspecific variability, demonstrating taxonomic inflation within this family. Our results also demonstrated the presence of cryptic diversity under the nominal species Physella acuta (Draparnaud, 1805), Beringophysa jennessi (Dall, 1919), Physella pomilia (Conrad, 1834), and Physella gyrina (Say, 1821).

Analyses of phylogeographic and population genetic structure of marine species with large population sizes, low fecundity, larval brooding, and limited dispersal such as the New Zealand flat oyster, Ostrea chilensis Küster, 1844, permit testing of the effects of historical and contemporary processes affecting patterns of coastal genetic differentiation and diversity. Analyses of DNA sequences from two mitochondrial DNA regions (COI, Cyt-b) compiled from O. chilensis individuals from 14 localities revealed a pronounced structure with three genetic clusters [Hauraki Gulf (HG); North; South] being resolved. These results suggest that historical processes have contributed to patterns of regional separation that have in turn contributed to regional genetic differences that are still observable today. Divergence time estimates of HG from North+South (1.97 Ma) and of North from South (0.36 Ma) indicate that O. chilensis from these regions represent evolutionarily significant units that evolved separately and rapidly in the early to middle Pleistocene. Analyses revealed no obvious periods of population expansion within any of the regions. These results contribute to a better understanding of how historical factors can result in pronounced mitochondrial DNA patterns of contemporary genetic structure and show how key life-history characteristics, e.g., larval brooding, can contribute to phylogeographic structure in coastal marine invertebrates.

In this paper, a taxonomic review of the bivalves of the genus Cuspidaria Nardo, 1840 from the southern southwestern Atlantic is conducted. Specimens deposited in malacological collections and samples collected onboard the R/V Puerto Deseado off Mar del Plata (∼36°S) and MPA Namuncurá/Burdwood Bank area (∼54°S), between 200 and 3,000 m depth, are the focus of this revision. The specimens were analyzed through conchological and anatomical features. The geographic and bathymetric distributions for each species are provided and possible factors determining biogeographic patterns are discussed. As a result, Cuspidaria infirma n. sp., Cuspidaria cancellata n. sp., Cuspidaria namuncura n. sp., and Cuspidaria cf. kerguelensis (Smith, 1885), are described. In addition, Cuspidaria exigua (Jeffreys, 1876), Cuspidaria bicarinata Jeffreys, 1882, Cuspidaria platensis (Smith, 1885), Cuspidaria tenella Smith, 1907, Cuspidaria infelix Thiele, 1912, and Cuspidaria barnardi Knudsen, 1970 are redescribed after the study of new specimens. Elliptic Fourier analyses were performed for each side of the shell to delimit species objectively using their shape. Results showed a clear differentiation on both valves among species. Cuspidaria bicarinata and Cuspidaria exigua, both North Atlantic species, were recorded for the first time in the southwestern Atlantic, and Cuspidaria infelix and Cuspidaria tenella, both Antarctic/sub-Antarctic species, expanded their distribution northwards. Two cluster analyses, for species and areas respectively, revealed a vertical zonation, separating species into two different groups highly corresponding to deep-sea water mass distributions.

We report a rare case of hyperstrophy in the intertidal turban snail Lunella correensis (Récluz, 1853), which was recently found in the collection of Kumagusu Minakata, a Japanese naturalist and folklorist. Although the soft-part anatomy is unknown, the combination of shell morphological characters indicate that the specimen is clearly dextral and hyperstrophic. Such variations in chilarity mostly hinder normal growth, hence an abnormal hyperstrophic adult individual is extremely rare. This mutation in chilarity is the first reported case of a hyperstrophic individual in Vetigastropoda.