A checklist of larval digeneans parasitising molluscs from inland waters of Argentina is presented here. Based on the bibliographical survey of 113 scientific articles and nine theses published between 1930 and 2021, 213 digeneans were found, which were distributed within 13 superfamilies and 35 families. The parasites were identified in 102 locations, encompassing eight of the sixteen biogeographical provinces in Argentina. Digeneans were found in 34 mollusc species (31 gastropods and three bivalves) belonging to 17 genera. The available data are presented for each digenean species, and included host information, localities, prevalence values, type of habitat, life cycle information (natural or experimental host), and information on material and genetic sequences deposited in repositories. Only 21.1% of individuals were identified to species level, and 8.5% to genus level. In addition, the genetic sequences of only 10 species (4.7%) were available at GenBank. This survey constitutes the first checklist of parasitic helminths in molluscs from inland waters of Argentina.

There is an important small-scale fishery using mechanized dredges and targeting clams (mainly wedge clam Donax trunculus and striped venus clam Chamelea gallina) along the Catalan coast (NW Mediterranean Sea). This study evaluated for the first time the discards and impact of mechanized clam dredging on the Catalan coast. To this end, three surveys were performed on board standard clam vessels (September and November 2016 and January 2017). Surveys were conducted in the three main clam fishing areas (Rosas Bay, South Barcelona and Ebro Delta). The composition of discards and the impact caused to discarded species was assessed using a three-level scale (undamaged; minor or partial damage; and lethal damage). Our study revealed that a large proportion of the catch (between 67–82% weight) is discarded. Even though about 63% of the discarded species were undamaged, 11% showed minor or partial damage and 26% lethal damage. Infaunal and epifaunal species with soft-body or fragile shells were the most impacted by the fishing activity (e.g. the sea urchin Echinocardium mediterraneum (~89%) and the bivalve Ensis minor (~74%)). Our results showed different levels of impact by target species and fishing area.

The most deleterious stage of a trematode life cycle occurs in the first intermediate host where the parasite penetrates as a miracidium and asexually multiplicates in sporocysts or rediae. When infection advances, other organs can be occupied with severe effects on host individual health and population dynamics. Existing studies focused on these host/parasite systems are still scarce due to the usual low prevalence in ecosystems. Using cockles (Cerastoderma spp.) and two trematode species (Monorchis parvus and Gymnophallus choledochus) infecting these bivalves as first and second intermediate host, the present work aimed to (1) summarize the most relevant literature and (2) provide new information regarding this host/parasite system, taking advantage of a 21-year monthly database from Banc d'Arguin (France). This long-term monitoring showed that different trematode species display varying host size range preference (6–38 and 31–36 mm for M. parvus and G. choledochus, respectively). The occurrence of coinfection was lower than expected, raising some questions related to parasite interspecific competition. This review improved our understanding of the processes shaping the prevalence and distribution of parasitism. This study highlighted that beyond constant trematode assemblage monitoring, there is a need to identify the main predictors of rediae/sporocysts infection, such as the definitive host dynamics and miracidium infection processes, for future better management of host severe disease and mortality episodes.

Haplosporidian protist parasites are a major concern for aquatic animal health, as they have been responsible for some of the most significant marine epizootics on record. Despite their impact on food security, aquaculture and ecosystem health, characterizing haplosporidian diversity, distributions and host range remains challenging. In this study, water filtering bivalve species, cockles Cerastoderma edule, mussels Mytilus spp. and Pacific oysters Crassostrea gigas, were screened using molecular genetic assays using deoxyribonucleic acid (DNA) markers for the Haplosporidia small subunit ribosomal deoxyribonucleic acid region. Two Haplosporidia species, both belonging to the Minchinia clade, were detected in C. edule and in the blue mussel Mytilus edulis in a new geographic range for the first time. No haplosporidians were detected in the C. gigas, Mediterranean mussel Mytilus galloprovincialis or Mytilus hybrids. These findings indicate that host selection and partitioning are occurring amongst cohabiting bivalve species. The detection of these Haplosporidia spp. raises questions as to whether they were always present, were introduced unintentionally via aquaculture and or shipping or were naturally introduced via water currents. These findings support an increase in the known diversity of a significant parasite group and highlight that parasite species may be present in marine environments but remain undetected, even in well-studied host species.

Understanding variations in the reproductive cycle of commercial and ecologically important bivalve species is essential to address fisheries management and climate oscillation issues. Spatial and temporal trends in the reproductive cycle of Callista chione were analysed using standard histological procedures and gonadosomatic index (GSI) for two consecutive years at two coastal sites in the Adriatic Sea. Reproductive output and fecundity were analysed quantitatively to gain better insight into the seasonal energy balance with respect to gametogenesis. A seawater temperature difference of ~4°C between the two sites likely influenced the onset and duration of spawning. At Cetina (milder temperatures), spawning was prolonged and occurred between spring and July, whereas at Pag there was only one main spawning peak in July. Both histology and GSI showed similar trends, indicating GSI to be a reliable method for analysing the main characteristics of the reproductive cycle. Conversely, the use of the body mass index (BMI) as an indicator of gonad development should be addressed carefully. Intraspecific variation in energy allocation between populations suggested life strategies modified to different habitat conditions. A higher reproductive investment and output in the Pag population directed gonadal resorption to ensure the generation of a new cycle, whereas the higher fecundity at the Cetina site indicated the production of gonads from newly available food. These results suggest successful physiological acclimatization to recent increasing temperatures.

The present paper, dedicated to the legacy of local geologist–engineer Peter Jozef (Sjeuf) Felder, who died in 2009, confirms his view that bioclasts constitute a valuable tool in the correlation of outcrops and borehole cores across the type area of the Maastrichtian Stage in the vicinity of Maastricht. His approach of interpreting changes in bioclast contents as having been influenced by Milankovitch cyclicity has here been applied successfully to the entire sedimentary complex of Maastrichtian (latest Cretaceous) age in the study area. In the present approach, results are corroborated by index fossils, mainly dinoflagellate cysts but also calcareous nannofossils, which allow correlation with the Stevns-1 core reference section in eastern Denmark. With the exception of local remnants of Belemnella obtusa Zone age, the Maastrichtian Stage in its type area encompasses the last 4.6 Ma of the Cretaceous Period (i.e. the Belemnella sumensis/Acanthoscaphites tridens Zone up to the K/Pg boundary). P.J. Felder's bioclast analyses have enabled the detection of twelve 400 kyr eccentricity cycles of Milankovitch cyclicity in the area. However, the section is not continuous; there is a hiatus of c.700 kyr between the Gulpen and Maastricht formations at the ENCI-HeidelbergCement Group quarry. In addition, smaller hiatuses, usually in the range of several 20 kyr cycles, have been detected in the upper Maastricht Formation.

Recent results suggest that bivalves can play an important role in restraining the spread of various aquatic infections. However, the ability of mussels to remove free-living stages of macroparasites and reduce their transmission is still understudied, especially for freshwater ecosystems. We investigated the influence of the common freshwater mussel (Anodonta anatina) on the transmission of a trematode (eye fluke, Diplostomum pseudospathaceum), which frequently infects fish in farms and natural habitats. In our experiments, mussels caused a significant decrease (P < 0·001) in the abundance of trematode free-living stages, from 6520 to 1770 cercariae L−1 on average (about 4-fold in 2 h). Individual clearance rates of mussels were 0·6‒3·7 L per hour (mean 1·9). These tests were followed by experimental infections of rainbow trout (Oncorhynchus mykiss) with different doses of D. pseudospathaceum cercariae in the presence or absence of mussels. Exposure of fish to cercariae in the presence of mussels significantly (P < 0·05) reduced the infection intensities in fish (by 30–40%) at all exposure doses. Our results indicate that freshwater bivalves can markedly reduce local cercariae densities and could be useful in mitigation of trematodoses harmful to fish farming.

Bivalve populations display fluctuating densities resulting in different interactions among them and with their environment. Using the edible cockle (Cerastoderma edule) as a model, we investigated two alternative hypotheses concerning the effect of density on individual infection intensity by trematode parasites. Considering that these parasites infect cockles through filtration activity, our first hypothesis was that high host density will have a dilution effect so that infection intensity decreases with host density. Conversely, high cockle density could attract other hosts used by these trematode parasites to complete their life cycle. A 17-year monthly survey of a cockle population in Arcachon Bay, France, showed a negative correlation between the cockle density and the abundance of parasite larvae in juvenile cockles with a significant threshold when adult cockle density reached 400 ind. m−2. This result was confirmed for the four dominating trematode parasites, independently considered. Additionally, a field experiment was performed during 9 months, with cockles maintained in enclosures with two densities (200 and 800 ind. m−2). Individual cockle mean infection was 1.5 times higher at low cockle density, mainly due to one dominant trematode species (Parvatrema minutum). In conclusion and confirming the first advanced hypothesis, for certain environments, negative consequences of bivalve intraspecific competition at high density can be mitigated by lower parasite pressure.

Amiantis purpurata shells from the San Matías Gulf (SMG) were analysed in order to compare both morphology and size throughout the late Quaternary in relation to environmental changes. Shells from modern beaches, Holocene marine assemblages (late Holocene, 3630 ± 100 years bp) and interglacial Pleistocene marine assemblages (MIS 5, 100 ka years bp) were studied by measuring the height and length, and using the elliptic Fourier analysis (EFA) to take an outline contour. The Pleistocene shells were smaller, more elliptical and with a deeper lunule than the Holocene and modern ones. No significant differences were recorded in the allometry index throughout the late Quaternary. The variation in size and shape of the A. purpurata shells could be related to the phenotypic plasticity of this species as a response to the environmental changes registered in the SMG during the Quaternary. These changes include variations in sea surface temperatures, salinities and substrates, and also water circulation changes, which would have modified nutrient availability. Morphological changes imply burrowing activity, mechanical stability, nutrient uptake and defence response to predation.

Nanoparticles have applications in a diverse range of products including medications, detergents, cosmetics, paint, sunscreen and electronics, with an economic worth projected to reach $2.5 trillion dollars in 2015. Research into the effects of manufactured nanomaterials on the environment, however, has failed to keep pace with the high volume of commercial production. Whereas a number of studies have examined the effects of nanoparticles on aquatic species, little work has focused on the way in which benthic marine species encounter, ingest and depurate these materials. The purpose of this study was to examine the ingestion and depuration of titania nanoparticles (anatase) by the blue mussel (Mytilus edulis) and the eastern oyster (Crassostrea virginica) during a spill scenario (an acute exposure to elevated concentrations). Bivalves were exposed to nanoparticles either incorporated into marine snow, an environmentally relevant medium for pollutants, or added directly to seawater at a concentration of 4.5 mg L−1 for 2 h. After feeding, the animals were transferred to filtered seawater and allowed to depurate. Faeces and tissues were collected at 0, 6, 24, 72 and 120 h, post-exposure, and analysed for concentrations of titanium by inductively coupled plasma-mass spectrometry. Results indicated that the capture and ingestion of titania nanoparticles by both species was not dependent on the method of delivery (incorporated into marine snow or freely suspended). Additionally, greater than 90% of the titania nanoparticles, on average, were eliminated from the tissues after 6 h, and only trace amounts remained after 72 h. These data demonstrate that mussels and oysters readily ingest titania nanoparticles, but rapidly depurate the material within hours of an acute exposure suggesting that little would be transferred to secondary consumers including humans. Further research is required to determine if other species of suspension-feeders handle titania nanoparticles in a manner similar to bivalves.

The pea crab Nepinnotheres villosulus is recorded for the first time from Sonmiani, Pakistan. It was found in six species of clams, Meretrix casta, Marcia recens, Callista umbonella, Gastrana multangula, Protapes cor and Psammotreta angulata and in one species of blood cockle, Anadara antiquate, with the highest prevalence in Meretrix casta. In some clams, both male and female crabs were found inside the host. More than 60% of female crabs were soft-shelled and ovigerous.

Marine invertebrate borings are very rare in crystalline rocks, providing evidence of particular strategies producers use to colonise these unfavourable substrates. In the Sorbas Basin (Almería, southern Spain), Upper Miocene transgressive successions contain blocks of metamorphic and igneous rocks of the Nevado–Filabride Complex of the Betic Cordillera. Ichnological analysis of the embedded blocks shows the presence of two types of macroborings located in gneiss boulders, revealed to be an extraordinary case worldwide. The most abundant are regular hemispherical depressions ascribed reservedly to the well-known, mostly bivalve boring Gastrochaenolites. The second one is a pouch-like depression, tapering downward, elliptical in outline, and clearly different to other non-circular-in-outline, pouch-shaped macroborings. Thus, a new ichnogenus and ichnospecies Cuenulites sorbasensis has been defined. According to the overall shape, an endolithic or semi-endolithic bivalve using chemical means to bore is suggested as the tracemaker. Colonisation could be determined by sea-level coastal dynamics, with decreasing energy during advancing transgression allowing boring, which was then stopped due to supply of fine-grained sediment that killed the borers.

The paramyxean parasite Marteilia refringens infects several bivalve species including European flat oysters Ostrea edulis and Mediterranean mussels Mytilus galloprovincialis. Sequence polymorphism allowed definition of three parasite types ‘M’, ‘O’ and ‘C’ preferably detected in oysters, mussels and cockles respectively. Transmission of the infection from infected bivalves to copepods Paracartia grani could be experimentally achieved but assays from copepods to bivalves failed. In order to contribute to the elucidation of the M. refringens life cycle, the dynamics of the infection was investigated in O. edulis, M. galloprovincialis and zooplankton over one year in Diana lagoon, Corsica (France). Flat oysters appeared non-infected while mussels were infected part of the year, showing highest prevalence in summertime. The parasite was detected by PCR in zooplankton particularly after the peak of prevalence in mussels. Several zooplanktonic groups including copepods, Cladocera, Appendicularia, Chaetognatha and Polychaeta appeared PCR positive. However, only the copepod species Paracartia latisetosa showed positive signal by in situ hybridization. Small parasite cells were observed in gonadal tissues of female copepods demonstrating for the first time that a copepod species other than P. grani can be infected with M. refringens. Molecular characterization of the parasite infecting mussels and zooplankton allowed the distinguishing of three Marteilia types in the lagoon.

The presence of the non-indigenous species, the black-pygmy mussel Limnoperna securis, was surveyed for the first time in the Rias of Pontevedra and Arousa, areas adjacent to the first location (Ria of Vigo) of this potential invader in Atlantic waters. Molecular identification of the mussels was conducted by polymerase chain reaction amplification and sequencing of nuclear and mitochondrial genes. This paper describes for the first time the species in the Ria of Pontevedra, confirming that this invader was absent in an intense shellfish farming area of the Ria of Arousa (Galicia, north-western Spain). Field sampling revealed that relatively high concentrations of this mytilid bivalve have colonized some localities of the inner part of the Ria of Pontevedra located in brackish waters. A comparison between population densities, size and substrate preference of L. securis in the Rias of Pontevedra and Vigo was conducted. Dispersion capacity of L. securis is discussed based on molecular detection of larval stages in the stomach contents of the copepod Centropages typicus coupled with physical oceanography of the southern Galician Rias. The invasive role of L. securis is also discussed in the context of the bissus secretion and attachment strength, ecological tolerance of the species, and the recent finding of settlements of this species on numerous colonies of the economically important blue mussel Mytilus galloprovincialis.

The composition and structure of a molluscan assemblage inhabiting an outcrop with a coralligenous community was studied in southern Spain. A total of 117 molluscan species were identified, with gastropods as the dominant group. Calyptraea chinensis was the dominant species and the family Conidae presented the highest number of species. The Shannon–Wiener diversity index and the Evenness showed non-significant changes between cold and warm months, displaying high values (~4 bits and ~0.8 bits respectively). Some of the dominant and/or frequent species are strictly associated with coralligenous-building organisms, such as Neosimnia spelta with gorgonians. Regarding trophic guilds, carnivores are the dominant group, followed by filter feeders due to the high abundance of C. chinensis. Regarding biogeographical distributions, most of these species (<95%) are widely distributed in European waters, the number of strictly Mediterranean species being very low. The Alboran Sea represents the distributional limit towards the Mediterranean for some species found in this bottom, such as the Atlantic Bela powisiana. Rocky–coralligenous bottoms are scarce in the western Alboran Sea but support a high species richness molluscan assemblage, displaying higher diversity values than the surrounding soft bottoms and increasing the biodiversity at local scale. This high biodiversity is partly explained by the coexistence of different taxa with contrasting biogeographical affinities promoted by the geographical location of the area. Due to this, conservation efforts should be required to protect this stretch of coastline where one of the most biodiverse invertebrate assemblages along the European coasts can be found.

The State of Santa Catarina in southern Brazil is the most important Brazilian producer region. The Pacific oysters Crassostrea gigas and the brown mussels Perna perna are the main species currently produced. The occurrence and impact of parasites on bivalves from natural or culture populations from Brazil are still poorly studied. This work describes several diseases, parasites and commensals from four edible bivalve species, from cultured and exploited stocks, from five sites at Santa Catarina State. Unspecific histopathological symptoms of stress, parasites and commensals were found, including viral gametocytic hypertrophy and rickettsia-like organisms with very low prevalences; the protozoan Nematopsis sp. with high prevalence and, ovarian parasites with low prevalences; and, diverse metazoans, such as turbellarian, sporocysts and metacercariae of trematodes, metacestoda larvae and spionid polychaete. Ray's fluid thioglycollate medium assays for detection of Perkinsus spp. did not detect any infected bivalves. Polymerase chain reaction assays for Marteiliodies chungmuensis in oysters with ovarian lesions produced negative results.

The impact of an alien species is correlated with its abundance and potential to colonisenew environments. Consequently, the crucial aspects that give a mytilid species invasivepotential include its strength and capacity for adhesion to a wide variety of substratesand its ecological tolerance to environmental conditions. The alien black pygmy musselXenostrobus securis settles together with the indigenous and raftcultured mussel Mytilus galloprovincialis on hard substrates of the innercoastline of the Ría de Vigo (Atlantic Coast NW Spain). Key parameters for the ecologicalsuccess of these species could include their byssus structure and ecological plasticity.In this study, we assessed their comparative ability to attach to different substratesunder different environmental conditions, using both in situ and laboratory approaches.Byssus threads secreted by X. securis were found to be extremely thin andtheir thickness did not vary with mussel size. This thinness of byssus filaments inX. securis was compensated by the secretion of a huge number (up tothousand of byssus filaments). Although no increase in attachment strength was found withincreasing mussel size in this species, multiple byssus thread secretion might be a keyfactor in the successful invasion of inner areas of the estuary. Furthermore, X.securis exposes a much lower shell area to lift and drag forces in musselconglomerates. By contrast, the indigenous species M. galloprovincialissecretes thicker byssus threads, which provide stronger in situ attachmentdisplaying a linear increase in strength relative to the size of mussels. The exposure ofboth mytilid species to different abiotic factors in the laboratory confirmed the weakerbyssus secretion and limited variation in attachment strength in the alien species. On onehand, X. securis seemed to be better adapted to life on soft bottoms andnot capable of much plasticity when attached to different substrates. However, X.securis might be also well adapted to variable environmental conditions, e.g.,salinity fluctuations, with no need to modify its byssus properties to ensure secureattachment. Attachment strength of M. galloprovincialis was higher thanX. securis in all abiotic conditions tested. Results are discussed inrelation to the ecological tolerance and impact of these mytilid species.

The present study reports new records of the invasive pygmy mussel Xenostrobus securis in six brackish-water localities in the western Mediterranean. Until now X. securis, whose native range includes southern Australia and New Zealand, was also known from the northern Adriatic Sea and southern France. Along the coast of northern Tuscany (Italy) X. securis invaded brackish-water canals in the area between the port of Leghorn and the mouth of the Arno River. Moreover, this mussel has been found in one inner site of the Gulf of Olbia (north-eastern Sardinia, Italy) and at the mouth of the Fluvià River (northern Catalonia, Spain). As an ecosystem engineer, X. securis is an ecologically important species, heavily altering pre-existing benthic communities. Given that its presence in other western Mediterranean sites is highly possible, we recommend a closer monitoring of brackish-water biotopes.

During studies of mangrove communities in central Vietnam (Nhatrang Bay, Tre Is and Dam Bay) a heterosexual pair of pontoniine shrimp, Neoanchistus cardiodytes, was found in the mantle cavity of the deeply burrowing bivalve Mactra grandis (Mactridae). This is the fourth record of pontoniine shrimps in symbiosis with burrowing bivalves, the second record of this species as well as its first record from Vietnam and the Pacific Ocean. A representative of the family Mactridae is firstly reported as a host for pontoniine shrimps and a new host for N. cardiodytes.