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Dinophysistoxin 1 (DTX1, 1) and okadaic acid (OA, 2) , produced by the dinoflagellates Dinophysis spp. and Prorocentrum spp. are primary diarrhetic shellfish toxins (DSTs), which may cause gastric illness in people consuming such as bivalves. Both compounds convert to dinophysistoxin 3 (DTX3, 3 ; generic name for 1 and 2 with fatty acids conjugated at 7-OH) in bivalves. The enzyme okadaic acid O -acyl transferase (OOAT) is a membrane protein found in the microsomes of the digestive glands of bivalves. In this study, we established an in vitro enzymatic conversion reaction using 4-nitro-2,1,3-benzoxadiazole (NBD)-OA (4), an OA derivative conjugated with (R)-(-)-4-nitro-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole (NBD-APy) on 1-CO2H, as a substrate. We detected the enzymatically produced 3 , NBD-7- O -palmitoyl-OA (NBD-Pal-OA), using high-performance liquid chromatography-fluorescence detection. We believe that an OOAT assay using 4 will facilitate the fractionation and isolation of OOAT in the future. [ABSTRACT FROM AUTHOR]

The freshwater mussels (Bivalvia: Unionida) of the biodiversity hotspot Sundaland are experiencing severe anthropogenic threats, whilst their diversity and distribution remain poorly understood. Here, we present the first modern-day data on Unionida diversity and distribution across western Borneo. Mussels were surveyed and collected in the upper Kapuas and Pawan river basins in West Kalimantan, Indonesia, and the Sambas Besar, Sarawak and Batang Sadong river basins in Sarawak, Malaysia. DNA sequencing (COI  + 16S +  ND1  + 18S + 28S) and morphological analyses were conducted to delineate and identify species, and reconstruct phylogenetic relationships and population genetics. Specimens belonged to six native genera and nine species, of which seven are endemic to Borneo and three are new to science, i.e. Ctenodesma mawonae Zieritz et al. sp. nov. Sarawak basin, and Ctenodesma bersinara Zieritz et al. sp. nov. and Rectidens lauris Zieritz et al. sp. nov. both Pawan basin. The monotypic genera Caudiculatus and Discomya were phylogenetically highly divergent from other known Gonideinae taxa, potentially indicating a separate tribe (for Caudiculatus) and subfamily (for Discomya). In addition, we report new records of the non-native Sinanodonta pacifica Heude, 1878 in the Batang Sadong and Kapuas river basins. [ABSTRACT FROM AUTHOR]

The Astartidae (Bivalvia) are a common benthic fossil in the British Lower Jurassic and as such it is important to understand their taxonomy so as to use them as a study system with which to consider environmental change through, and extinction events in, this epoch. The majority of the species of the Astartidae from the British Lower Jurassic are taxa within the subfamily Astartinae, encompassing the genera Neocrassina, Coelastarte and Oxyeurax. There has been some question as to whether those shells attributed to Neocrassina could be further split, with two species assigned to this genus having some characters that are atypical. We prefer to retain the atypical species within ? Neocrassina , the genus with which they have the greatest affinity, rather than erect another genus. This study assigns the suite of British Lower Jurassic fossil bivalves attributed to Nicaniella to Oxyeurax , based on the presence of a poorly defined 3a tooth and form of commarginal ridge ornament. Differentiation at the species level in Astartinae is complicated; the subfamily exhibits generally low disparity compared with other bivalves, compounded by ecomorphological effects and, in some cases, sexual dimorphism. We show that the Neocrassina lineage exhibits gradual changes in shape, as well as hinge plate development and complexity, through the Lower Jurassic, and identify potential sexual dimorphism in species of Oxyeurax. The temporally overlapping species of Oxyeurax display varying degrees of ornamental development which may well be environmentally controlled and are used in this study to define distinct new species. This study recognizes 12 distinct species of Astartinae from the British Lower Jurassic. Nine are established taxa (Neocrassina elegans, N. expansa, N. gueuxii, N. lurida, N. phaedra , ? N. camertonensis , ? N. dentilabrum, Oxyeurax duplicata, O. striatosulcata), whilstthree are new species (Coelastarte wardenensis, O. mickletonensis and Oxyeurax thompsoni). Only two of the British Lower Jurassic Astartinae species appear to have survived the global Early Toarcian extinction event as represented in British successions; one Neocrassina and one Oxyeurax. However, the lack of fossiliferous, high energy near shore environments in the early Toarcian may bias this observation, especially for Oxyeurax. [ABSTRACT FROM AUTHOR]

The subfamily Sphaeriinae is a diverse and ecologically significant group of freshwater invertebrates, playing a keystone role in the energy flow and nutrient cycling in aquatic ecosystems. Despite a long history of its study, the taxonomic structure and species content of this group are a matter of ongoing disputes between malacologists. We clarify the taxonomy, distribution, and evolutionary biogeography of the Sphaeriinae around the world based on the largest dataset of DNA sequences of these clams ever accumulated, which includes the data on specimens collected from various continents and countries around the globe. Our 16S rRNA and two-locus phylogenies reveal that the Sphaeriinae is a monophyletic group, containing at least seven genus-level clades: Sphaerium Scopoli, 1777, Pisidium C. Pfeifffer, 1821 (s.s.), Euglesa Jenyns, 1832, Odhneripisidium Kuiper, 1962, Conventus Pirogov & Starobogatov stat. nov. 1974, 'Pisidium' sterkianum group, and Hindupisidium Vinarski & Bespalaya gen. nov. Our 16S rRNA phylogenetic tree contains 80 well-supported clades corresponding to the putative species-level taxa. Four species new to science are described here: Euglesa kolymensis Bespalaya, Aksenova & Bolotov sp. nov. , Euglesa kyrgyzica Bespalaya, Aksenova, Kondakov & Palatov sp. nov. , Euglesa moroccana Bespalaya, Vinarski, Aksenova, Mabrouki, Kondakov & Palatov sp. nov. , Odhneripisidium caucasus Bespalaya, Vinarski, Aksenova, Kondakov & Palatov sp. nov. Our fossil-calibrated phylogeny and generalized biogeographic model indicate that the most recent common ancestor of the Sphaeriidae could have originated somewhere within a broad area covering China near the Lower Cretaceous boundary. [ABSTRACT FROM AUTHOR]

Dead coral rocks are prevalent hard substrates in shallow warm waters, providing habitat for various infaunal and boring invertebrates. Despite this, the nature of species interactions, especially symbiotic relationships, among them remains poorly understood. Bonellia (Annelida: Thalassematidae: Bonelliinae) is a group of greenish echiuran worms commonly inhabiting cavities inside dead coral rocks. Although echiuran burrows in marine sediments are known to harbour various host-specific macrosymbionts, it remains unclear whether such associations also occur in hard substrates. To address this, we investigated the diversity of macrosymbionts associated with the burrows of Bonellia sp. aff. minor in the warm-temperate coast of the Kii Peninsula, Japan, and the evolutionary origins of those symbionts. The host's burrow morphology was also examined using micro-computed tomography (CT) scanning. Our field survey revealed that the burrows of Bo. sp. aff. minor hosted three commensal species including a polychaete, Oxydromus fauveli , and two new species, a bivalve (Basterotia bonelliphila sp. nov.) and an amphipod (Leucothoe bonelliae sp. nov.). Our molecular phylogenetic analyses showed that each symbiont species belongs to a clade comprising commensal species specific to echiurans or annelids. Overall, our findings contribute to a better understanding of symbiotic associations in marine hard substrates. [ABSTRACT FROM AUTHOR]

The shell of bivalves acts as structural support, defence against predators, stressors, and maintenance of homeostasis. Haemocytes and mantle epithelial cells participate in shell formation. Mantle epithelial cells produce the organic matrix of the shell and are associated with biomineralization because of their proximity to the shell surface and ability to maintain shell deposition ex vivo. Haemocytes play an immunological role and are involved in Ca2+ and CO32- intracellular transport implicated in shell mineralization. This study aims to evaluate the expression of molecules that play key roles in internal defence and the nervous system, in epithelial cells and haemocytes of the outer mantle margin of two species of bivalves, Polititapes aureus Gmelin, 1791 and Cerastoderma glaucum Bruguière, 1789, to highlight their collaborative role in shell formation. Our data show for the first time the presence of serotonin/S100 protein, and TLR2/iNOS colocalization in the haemocytes and mantle epithelial cells of P. aureus and C. glaucum , suggesting that the mantle cells perform their canonical role of sensory and biomineralizing activity, while the haemocytes perform their typical immune function, and their collaboration in shell formation, providing new information on cellular interactions in shell formation and giving more details for taxonomical studies. [ABSTRACT FROM AUTHOR]

Cyrtopleura costata is a pholadid bivalve that inhabits tidal flats inside burrows c. 40 cm deep, and its visceral mass outgrows its shell significantly. Thus, unlike other bivalves, it cannot isolate its soft tissues from the external environment through complete valve closure. One can thus hypothesize that this bivalve would be inevitably more exposed and susceptible to the tidal changes in salinity. No information regarding its osmoregulatory physiology has been found in the literature. We thus investigated how its fluids would respond to seawater dilution and seawater concentration, and how its tissues would be able to keep their moisture content. Individuals of C. costata were acclimated to 30‰ and then independently exposed stepwise (1 h for each 5‰ change) to 25, 20, 15 and 10‰ or to 35, 40, 45 and 50‰. Isolated tissue slices obtained from control animals (30‰) of siphon, mantle and muscle were exposed in vitro to salines corresponding to salinities of 10, 30 and 50‰. Cyrtopleura costata responded as a typical euryhaline osmoconformer between 25 and 40‰, with haemolymph and mantle cavity water being isosmotic to the external medium. However, some 'buffering' of haemolymph osmolality was displayed in the most extreme salinities, 10–20‰ and 45–50‰. This could result from muscle contraction and other cellular responses, reducing 'apparent permeability' and diffusive fluxes; the muscle was the tissue with the highest capacity to maintain constant hydration despite significant osmotic challenge. Both in vivo and in vitro experiments indicated a higher tolerance of salinity increases than decreases. Thus, if global and local changes in climate and precipitation rates result in more frequent seawater dilution in its habitat, the area occupied by its realized niche may be reduced. [ABSTRACT FROM AUTHOR]

Hiatella is among the most poorly understood bivalve genera. Most of the species remain known only from shell morphology, which has proved to be extremely variable in the group. Few studies have addressed their anatomy and biology, and no studies have combined morphological, anatomical and biological characters with molecular characters. This has led to the hiatellids all around the world being regarded as a single, widely distributed species. This contribution represents a step towards a better understanding of hiatellids worldwide by providing the first integrative study of the species occurring in southern South America. Three entities are recognized: Hiatella meridionalis , Hiatella barnea and Hiatella umbonata sp. nov. To understand their intraspecific variability, all the species are carefully described and figured, based on large series of specimens. Saxicava chilensis , Saxicava mollis , Saxicava lebruni and Saxicava subantarctica are considered synonyms of H. meridionalis ; a lectotype for S. subantarctica is designated; and S. antarctica and S. frigida are regarded as nomina dubia. This study suggests that worldwide living hiatellids might have originated from South American species and that reduction/loss of hinge teeth during ontogeny and life on hard substrates or on/inside other invertebrates would represent derived traits within the genus Hiatella. [ABSTRACT FROM AUTHOR]

We describe the use of abraded bivalve shells by the shellback crabs Hypoconcha arcuata Stimpson, 1858 and H. parasitica (Linnaeus, 1763) in southeastern Brazil. Shells from four species of bivalves were associated with the crabs: Eucallista purpurata (Lamarck, 1818), Chionopsis crenata (Gmelin, 1791), and Tivela zonaria (Lamarck, 1818) (Veneridae), and, most frequently (50%), Dallocardia delicatula (E.A. Smith, 1915) (Cardiidae). This was the first documented record of shellback crabs using valves of veneriid bivalves, as well as the first report of a crab-shell association for Hypoconcha in the South Atlantic Ocean. The relationship between the increase in size of shellback crabs and the size of the chosen shell was discussed. [ABSTRACT FROM AUTHOR]

Among Metazoa, bivalves have the highest lifespan disparity, ranging from 1 to 500+ years, making them an exceptional testing ground to understand mechanisms underlying aging and the evolution of extended longevity. Nevertheless, comparative molecular evolution has been an overlooked approach in this instance. Here, we leveraged transcriptomic resources spanning 30 bivalve species to unravel the signatures of convergent molecular evolution in four long-lived species: Margaritifera margaritifera , Elliptio complanata , Lampsilis siliquoidea , and Arctica islandica (the latter represents the longest-lived noncolonial metazoan known so far). We applied a comprehensive approach—which included inference of convergent dN/dS, convergent positive selection, and convergent amino acid substitution—with a strong focus on the reduction of false positives. Genes with convergent evolution in long-lived bivalves show more physical and functional interactions to each other than expected, suggesting that they are biologically connected; this interaction network is enriched in genes for which a role in longevity has been experimentally supported in other species. This suggests that genes in the network are involved in extended longevity in bivalves and, consequently, that the mechanisms underlying extended longevity are—at least partially—shared across Metazoa. Although we believe that an integration of different genes and pathways is required for the extended longevity phenotype, we highlight the potential central roles of genes involved in cell proliferation control, translational machinery, and response to hypoxia, in lifespan extension. [ABSTRACT FROM AUTHOR]

Genetic elements encoded in nuclear DNA determine the sex of an individual in many animals. In certain bivalve lineages that possess doubly uniparental inheritance (DUI), mitochondrial DNA (mtDNA) has been hypothesized to contribute to sex determination. In these cases, females transmit a female mtDNA to all offspring, while male mtDNA (M mtDNA) is transmitted only from fathers to sons. Because M mtDNA is inherited in the same way as Y chromosomes, it has been hypothesized that mtDNA may be responsible for sex determination. However, the role of mitochondrial and nuclear genes in sex determination has yet to be validated in DUI bivalves. In this study, we used DNA, RNA, and mitochondrial short noncoding RNA (sncRNA) sequencing to explore the role of mitochondrial and nuclear elements in the sexual development pathway of the freshwater mussel Potamilus streckersoni (Bivalvia: Unionida). We found that the M mtDNA sheds a sncRNA partially within a male-specific mitochondrial gene that targets a pathway hypothesized to be involved in female development and mitophagy. RNA-seq confirmed the gene target was significantly upregulated in females, supporting a direct role of mitochondrial sncRNAs in gene silencing. These findings support the hypothesis that M mtDNA inhibits female development. Genome-wide patterns of genetic differentiation and heterozygosity did not support a nuclear sex-determining region, although we cannot reject that nuclear factors are involved with sex determination. Our results provide further evidence that mitochondrial loci contribute to diverse, nonrespiratory functions and additional insights into an unorthodox sex-determining system. [ABSTRACT FROM AUTHOR]

Bivalves are a diverse group of molluscs that have recently attained a central role in plenty of biological research fields, thanks to their peculiar life history traits. Here, we propose that bivalves should be considered as emerging model systems also in sex-determination (SD) studies, since they would allow to investigate: 1) the transition between environmental and genetic SD, with respect to different reproductive backgrounds and sexual systems (from species with strict gonochorism to species with various forms of hermaphroditism); 2) the genomic evolution of sex chromosomes (SCs), considering that no heteromorphic SCs are currently known and that homomorphic SCs have been identified only in a few species of scallops; 3) the putative role of mitochondria at some level of the SD signaling pathway, in a mechanism that may resemble the cytoplasmatic male sterility of plants; 4) the evolutionary history of SD-related gene (SRG) families with respect to other animal groups. In particular, we think that this last topic may lay the foundations for expanding our understanding of bivalve SD, as our current knowledge is quite fragmented and limited to a few species. As a matter of fact, tracing the phylogenetic history and diversity of SRG families (such as the Dmrt , Sox , and Fox genes) would allow not only to perform more targeted functional experiments and genomic analyses, but also to foster the possibility of establishing a solid comparative framework. [ABSTRACT FROM AUTHOR]

Most organisms possess the capacity to metabolize arsenic (As) accumulating compounds to less toxic forms, thus minimizing the adverse effect induced by this metalloid. However, other contaminants may to interfere with As metabolism, contributing to the accumulation of more toxic compounds. Microplastics (MPs) are omnipresent in aquatic environment and may induce toxicological effects (alone or in combination with other contaminants) on living organisms. Therefore, the objective of the present study was to evaluate the effect of the exposure of the freshwater clam Limnoperna fortunei to a combination of MP (4 and 40 μg/L of polystyrene microbeads, 1.05 μm) and As (50 μg/L) for 48 h, evaluating the accumulation and metabolization of As and oxidative stress parameters, such as catalase (CAT), glutathione-S-transferase activities, total antioxidant competence, reduced glutathione (GSH), and lipid damage in the gills and digestive glands. Results revealed that low MP concentration disrupts the redox state of the digestive gland by a decrease in the antioxidant activity (CAT and total antioxidant capacity). GSH levels in the gills of animals exposed to MP (4 μg/L) alone and the combination of MP + As increased, concomitant with an increase in the percentage of toxic compounds, indicating the effect of MP on As metabolism. Although, few studies evaluated the effect of coexposure to MP + As by considering metabolization of metalloid in freshwater bivalve, our results revealed that exposure to MP reduced the metabolization capacity of As, favoring the accumulation of more toxic compounds besides the MP alone, which showed a pro-oxidant effect in L. fortunei. [ABSTRACT FROM AUTHOR]

Siphons represent a remarkable example of evolutionary convergence in different bivalve lineages. In Protobranchia, the siphons, when present, are used exclusively to channel the water currents used for respiration, waste removal and gamete release. Their emergence is thought to be associated with the taxonomic and morphological diversification within the Nuculanida. While siphons have been extensively studied in other bivalve groups, particularly the Heterodonta, gaps remain in the knowledge of protobranch siphons, especially on their morphology, including the musculature and innervation, and their functioning. The few data on Protobranchia siphons are restricted to some Nuculanoidea, and information is still missing for other nuculanid lineages, such as the Sareptoidea. The present study provides a description of the siphonal morphology of Aequiyoldia eightsii , a sareptid bivalve. Histological data were obtained to investigate their organization and infer their functioning. All traits observed were compared with those of heterodont siphons. In A. eightsii , the siphons are fused with each other and distinguished by their reduced longitudinal musculature in bundles that do not form layers, by the presence of a blood lacunal system that fills most of the wall of the siphon and by the innervation that is likely diffuse. This suggests that the siphons are hydrostatic organs with a hydraulic mechanism whose expansion occurs when the lacunar system is filled with blood. Our results provide the first morphological and functional details of a protobranch siphon and thus contribute to knowledge on the comparative anatomy of Bivalvia. [ABSTRACT FROM AUTHOR]

Foot inflation and protrusion in bivalve molluscs is part of a sequence of events necessary for burrowing into the substrate. Although this process been observed after exogenous exposure to the neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] and by some selective serotonin reuptake inhibitor (SSRI) type antidepressants, no study has shown that foot inflation and protrusion as a precursor to burrowing is under serotonergic control. In order to elucidate the physiological mechanism mediating this response, we tested over 2,000 freshwater bivalves in three species by exposing them to 5-HT, two 5-HT receptor agonists, two receptor antagonists and five antidepressants. Fingernail clams (Sphaerium striatinum), Asian clams (Corbicula fluminea) and unionid mussels (Elliptio complanata) all showed significant foot inflation or foot protrusion when exposed to 5-HT and the serotonergic agonists 8-OH-DPAT and alpha-methyl 5-HT. Some SSRI-type antidepressants (fluoxetine and fluvoxamine) also significantly induced these responses in all three species but were not as potent at the concentrations tested. In S. striatinum and C. fluminea , a 2-h exposure to the 5-HT2 receptor antagonists mianserin and cyproheptadine effectively blocked foot inflation induced by 5-HT and 8-OH-DPAT. The 5-HT receptor mediating this response is thus sensitive to mammalian 5-HT1 and 5-HT2 receptor ligands, supporting the hypothesis that serotonin mediates the initial step in burrowing. [ABSTRACT FROM AUTHOR]

Truncilla macrodon ¸ the Texas Fawnsfoot, is currently considered to be restricted to the Brazos and Colorado river drainages in central Texas, USA. Subfossil specimens resembling T. macrodon from shell middens in the Trinity river drainage have raised questions about its presumptive range. Extant Truncilla populations occupying the Trinity river drainage are believed to be Truncilla donaciformis , the Fawnsfoot, but the species identity has not been assessed using molecular techniques. In this study, we set out to use phylogeographic and morphometric approaches to resolve the distribution of Truncilla spp. in Texas, with an emphasis on assessing species identity of Truncilla in the Trinity river drainage. Our molecular analyses indicated individuals from the Trinity river drainage are T. macrodon rather than T. donaciformis , and morphometric analyses using ratios of shell length, width and height supports this finding and showed differentiation among T. macrodon, Truncilla cognata and T. donaciformis. These combined findings suggest the range of T. macrodon is larger than previously recognized and includes the Colorado, Brazos and Trinity river drainages. The status of Truncilla spp. in the San Jacinto river basin remains unclear due to lack of information on historical or extant populations, but we recommend conservationists consider T. macrodon as part of the mussel fauna since the drainage shares an embayment with the Trinity river drainage. Molecular data also indicated the Trinity population of T. macrodon is distinct from, and more genetically diverse than, the Brazos and Colorado populations. This difference suggests the Trinity River population should be treated as a separate management unit from the Brazos and Colorado River populations to facilitate effective conservation and recovery planning. Our study adds to the growing body of literature highlighting the utility of molecular data in conservation and management of freshwater mussels. [ABSTRACT FROM AUTHOR]

The morphological disparity of the marine benthos, through the Phanerozoic, is shaped by multiple abiotic and biotic factors, among which substrate and ecology are key contributors. However, the relationship among substrate, ecology, and morphology is not straightforward—a substrate can be occupied by phylogenetically unrelated families with different life habits, influencing morphological convergence. In contrast, related taxa may differ in substrate and life habits, indicating morphological divergence. Here we evaluate the effect of substrate and ecology on the community-level morphological disparity of 398 Recent marine bivalve species from coastal India, using geometric morphometrics. We further evaluate whether the observed patterns are decoupled from taxonomic identities, i.e. phylogenetic (in)dependence. We find that the Recent marine bivalve assemblages show significant morphological differences while living in different substrates or having different life habit traits. However, while sharing a specific substrate or life habit trait (tiering/motility), different families do not show shape convergence, i.e. families maintain their mean shape, except for families living in soft sediments, for which they show strong substrate-driven morphological convergence. These instances of morphological divergence and convergence suggest that the association among sediment preference, ecology, and shape can be rather complex, and can often transgress phylogenetic boundaries in bivalves. [ABSTRACT FROM AUTHOR]

Inaccurate taxonomy can lead to species in need of conservation being overlooked, which makes revisionary systematics crucially important for imperilled groups. The freshwater mussel genus Alasmidonta is one such group in need of study. Here, we take a multilocus phylogenetic approach to assess species-level taxonomy of Alasmidonta and test monophyly of this genus. Phylogenetic inference resulted in polyphyly of Alasmidonta. Lasmigona , which was included to test monophyly of Alasmidonta , was also polyphyletic. Species delimitation methods disagreed about whether Alasmidonta arcula , Alasmidonta triangulata and Alasmidonta undulata are distinct species, but all delimitation methods agreed that Alasmidonta harbours an undescribed species that would be considered Alasmidonta varicosa under current taxonomy. Given conflict among species delimitation methods and geographical separation, we maintain the current taxonomy for A. arcula and A. triangulata. The undescribed species is restricted to rivers of the Uwharrie Mountains region in North Carolina, USA that flow into the Pee Dee River from the east and can be distinguished morphologically from A. varciosa by higher and wider placed adductor mussels and a hooked pseudocardinal tooth. We offer insights into how supraspecific taxonomy of subtribe Alasmidontina might be resolved and formally describe the lineage from the Uwharrie Mountains region as Uwharrie elktoe, Alasmidonta uwharriensis sp. nov. [ABSTRACT FROM AUTHOR]

Toll-like receptors (TLRs) are the most widespread class of membrane-bound innate immune receptors, responsible of specific pathogen recognition and production of immune effectors through the activation of intracellular signaling cascades. The repertoire of TLRs was analyzed in 85 metazoans, enriched on molluscan species, an underrepresented phylum in previous studies. Following an ancient evolutionary origin, suggested by the presence of TLR genes in Anthozoa (Cnidaria), these receptors underwent multiple independent gene family expansions, the most significant of which occurred in bivalve molluscs. Marine mussels (Mytilus spp.) had the largest TLR repertoire in the animal kingdom, with evidence of several lineage-specific expanded TLR subfamilies with different degrees of orthology conservation within bivalves. Phylogenetic analyses revealed that bivalve TLR repertoires were more diversified than their counterparts in deuterostomes or ecdysozoans. The complex evolutionary history of TLRs, characterized by lineage-specific expansions and losses, along with episodic positive selection acting on the extracellular recognition domains, suggests that functional diversification might be a leading evolutionary force. We analyzed a comprehensive transcriptomic data set from Mytilus galloprovincialis and built transcriptomic correlation clusters with the TLRs expressed in gills and in hemocytes. The implication of specific TLRs in different immune pathways was evidenced, as well as their specific modulation in response to different biotic and abiotic stimuli. We propose that, in a similar fashion to the remarkable functional specialization of vertebrate TLRs, the expansion of the TLR gene family in bivalves attends to a functional specification motivated by the biological particularities of these organisms and their living environment. [ABSTRACT FROM AUTHOR]

In most animals, mitochondrial DNA is strictly maternally inherited and non-recombining. One exception to this pattern is called doubly uniparental inheritance (DUI), a phenomenon involving the independent transmission of female and male mitochondrial genomes. DUI is known only from the molluskan class Bivalvia. The phylogenetic distribution of male-transmitted mitochondrial DNA (M mtDNA) in bivalves is consistent with several evolutionary scenarios, including multiple independent gains, losses, and varying degrees of recombination with female-transmitted mitochondrial DNA (F mtDNA). In this study, we use phylogenetic methods to test M mtDNA origination hypotheses and infer the prevalence of mitochondrial recombination in bivalves with DUI. Phylogenetic modeling using site concordance factors supported a single origin of M mtDNA in bivalves coupled with recombination acting over long evolutionary timescales. Ongoing mitochondrial recombination is present in Mytilida and Venerida, which results in a pattern of concerted evolution of F mtDNA and M mtDNA. Mitochondrial recombination could be favored to offset the deleterious effects of asexual inheritance and maintain mitonuclear compatibility across tissues. Cardiida and Unionida have gone without recent recombination, possibly due to an extension of the COX2 gene in male mitochondrial DNA. The loss of recombination could be connected to the role of M mtDNA in sex determination or sexual development. Our results support that recombination events may occur throughout the mitochondrial genomes of DUI species. Future investigations may reveal more complex patterns of inheritance of recombinants, which could explain the retention of signal for a single origination of M mtDNA in protein-coding genes. [ABSTRACT FROM AUTHOR]

Google Scholar Crossref Search ADS PubMed WorldCat 2 BENTHOTAGE C., COLE V.J., SCHULZ K.G., BENKENDORFF K. 2020. Google Scholar Crossref Search ADS PubMed WorldCat 28 KOLMOGOROV M., BICKHART D.M., BEHSAZ B., GUREVICH A., RAYKO M., SHIN S.B., KUHN K., YUAN J., POLEVIKOV E., SMITH T.P.L., PEVZNER P.A. 2020. metaFlye: scalable long-read metagenome assembly using repeat graphs. Google Scholar Crossref Search ADS WorldCat 3 BERNT M., BRABAND A., SCHIERWATER B., STADLER P.F. 2013a. Genetic aspects of mitochondrial genome evolution. Google Scholar Crossref Search ADS Google Preview WorldCat COPAC 48 STÖGER I., SCHRÖDL M. 2013. [Extracted from the article]

Background: Given the recent detection of tetrodotoxin (TTX) in bivalve molluscs but the absence of a full collaborative validation study for TTX determination in a large number of shellfish samples, interlaboratory assessment of method performance was required to better understand current capabilities for accurate and reproducible TTX quantitation using chemical and immunoassay methods. Objective: The aim was to conduct an interlaboratory study with multiple laboratories, using results to assess method performance and acceptability of different TTX testing methods. Methods: Homogenous and stable mussel and oyster materials were assessed by participants using a range of published and in-house detection methods to determine mean TTX concentrations. Data were used to calculate recoveries, repeatability, and reproducibility, together with participant acceptability z-scores. Results: Method performance characteristics were good, showing excellent sensitivity, recovery, and repeatability. Acceptable reproducibility was evidenced by HorRat values for all LC-MS/MS and ELISA methods being less than the 2.0 limit of acceptability. Method differences between the LC-MS/MS participants did not result in statistically different results. Method performance characteristics compared well with previously published single-laboratory validated methods and no statistical difference was found in results returned by ELISA in comparison with LC-MS/MS. Conclusion: The results from this study demonstrate that current LC-MS/MS methods and ELISA are on the whole capable of sensitive, accurate, and reproducible TTX quantitation in shellfish. Further work is recommended to expand the number of laboratories testing ELISA and to standardize an LC-MS/MS protocol to further improve interlaboratory precision. Highlights: Multiple mass spectrometric methods and a commercial ELISA have been successfully assessed through an interlaboratory study, demonstrating excellent performance. [ABSTRACT FROM AUTHOR]

Phosphate mineralization as a skeletal material is uncommon in invertebrate animals and rare in Mollusca. Remarkably, apatite minerals were first reported more than 30 years ago in the periostracum of two species of the mytilid bivalve Lithophaga where shells are mostly constructed of calcium carbonate. This discovery extended the range of biominerals secreted by molluscs but has attracted no subsequent research. In this study we review the occurrence of phosphate mineralization in Lithophaga and putatively allied taxa. Lithophagine bivalves, particularly Lithophaga and the more diverse Leiosolenus species, are well known for their endolithic chemical dissolution of calcareous rocks and corals with calcium-binding lipoproteins secreted by mantle glands. Fluorapatite was identified by X-ray diffraction in an outer layer of the periostracum in six species of Lithophaga. Morphological study by scanning electron microscopy of four species showed the fluorapatite crystals embedded in periostracal material in a layer 10–20 µm thick. Dilute bleach treatment revealed the crystals as densely packed euhedral prisms 250–400 nm in size. The succeeding inner layers of the periostracum were unmineralized. Observations of the developing periostracum of Lithophaga teres suggest that the initial mineralization is in the form of amorphous granules that coalesce and transform into euhedral crystals. Periostracal phosphate was not recorded in other members of the Lithophaginae – Leiosolenus , Botula or Zelithophaga species. Leiosolenus species characteristically have extraperiostracal aragonitic encrustations that can be thick and structurally complex. Published molecular phylogenies of Mytilidae bivalves show a division into two major clades with Lithophaga species in one clade and Leiosolenus species in the other, indicating that the subfamily Lithophaginae as presently understood is polyphyletic. This result implies that the two genera have independent evolutionary pathways to endolithic occupation of calcareous substrates although using similar mantle gland secretions to excavate their crypts. Because fluorapatite is considerably less soluble and harder than calcium carbonate, it is suggested that the phosphate layer of Lithophaga is a functional adaptation to protect their shells from self-dissolution from their rock-dissolving glandular secretions and may also act as defence against other shell-eroding organisms. [ABSTRACT FROM AUTHOR]

This comparative study assessed hepatitis A virus (HAV) contamination in shellfish harvesting areas in Morocco, and the correlations between viral contamination and rainfall. To this aim, HAV contamination was evaluated in 156 shellfish samples collected at three Moroccan coastal areas (52 samples/area): Dakhla (class A), Oualidia (class B), and Moulay Bousselham (class C). Samples were collected monthly between March 2018 and March 2019, and included oysters from different farms at the Oualidia and Dakhla coastal areas, and wild mussels at the Moulay Bousselham lagoon. HAV was detected by RT-qPCR in 24/156 (15.38%) samples: 16/145 (11.03%) mussel (Mytillus galloprovincialis) and 8/156 (5.13%) oyster (Crassostea gigas) samples. The 16 mussel-positive samples (16/52) were collected at Moulay Bousselham, and the eight oyster-positive samples (8/52) were collected at Oualidia, and none at Dakhla (class A). The highest HAV contamination rate was recorded at Moulay Bousselham lagoon (class C) (30.77%), while it did not exceed 8% at Oualidia (class A). A nonsignificant, positive correlation between HAV-positive samples and mean rainfall was observed. The important HAV presence in bivalve mollusks from the Oualidia and Moulay Bousselham lagoons indicate the need of viral surveillance of bivalve mollusks and of improving wastewater quality to enhance shellfish safety. [ABSTRACT FROM AUTHOR]

There are increasing findings of the bivalve transmissible neoplasia derived from the Pacific mussel Mytilus trossulus (Mtr BTN) in populations of different Mytilus species worldwide. The Subarctic is an area where this disease has not yet been sought despite the fact that Mytilus spp. are widespread there, and M. trossulus itself is a boreal species. We used flow cytometry of the hemolymph, hemocytology, and histology to diagnose disseminated neoplasia in a sample of M. trossulus from Magadan in the subarctic Sea of Okhotsk. Neoplasia was identified in 11 of 214 mussels studied. Using mtDNA COI sequencing, we revealed genotypes identical or nearly identical to known Mtr BTN ones in the hemolymph of most of the diseased mussels. Both Mtr BTN evolutionary lineages have been identified, the widespread Mtr BTN2, and Mtr BTN1, so far only known from M. trossulus in British Columbia on the other side of the Pacific from Magadan. In addition, Mtr BTN2 was represented by 2 common diverged mtDNA haplolineages. These conclusions were confirmed for selected cancerous mussels by molecular cloning of COI and additional nuclear and mtDNA genes. On the background of high genetic diversity, different cancers were similar in terms of ploidy (range 4.0–5.8 n) and nuclear-to-cell ratio. Our study provides the first description of neoplasia and Mtr BTN in mussels from the Sea of Okhotsk and from the Subarctic, of both Mtr BTN1 and Mtr BTN2 in the same mussel population, and the first direct comparison between these transmissible cancers. [ABSTRACT FROM AUTHOR]

Freshwater Unionid bivalves have recently faced ecological upheaval through pollution, barriers to dispersal, harvesting, and changes in fish–host prevalence. Currently, over 70% of species in North America are threatened, endangered or extinct. To characterize the genetic response to recent selective pressures, we collected population genetic data for one successful bivalve species, Megalonaias nervosa. We identify megabase-sized regions that are nearly monomorphic across the population, signals of strong, recent selection reshaping diversity across 73 Mb total. These signatures of selection are greater than is commonly seen in population genetic models. We observe 102 duplicate genes with high d N /d S on terminal branches among regions with sweeps, suggesting that gene duplication is a causative mechanism of recent adaptation in M. nervosa. Genes in sweeps reflect functional classes important for Unionid survival, including anticoagulation genes important for fish host parasitization, detox genes, mitochondria management, and shell formation. We identify sweeps in regions with no known functional impacts, suggesting mechanisms of adaptation that deserve greater attention in future work on species survival. In contrast, polymorphic transposable elements (TEs) appear to be detrimental and underrepresented among regions with sweeps. TE site frequency spectra are skewed toward singleton variants, and TEs among regions with sweeps are present at low frequency. Our work suggests that duplicate genes are an essential source of genetic novelty that has helped this species succeed in environments where others have struggled. These results suggest that gene duplications deserve greater attention in non-model population genomics, especially in species that have recently faced sudden environmental challenges. [ABSTRACT FROM AUTHOR]

Currently, the validity of many nominal bivalve species of the genus Corbicula endemic to the Russian Far East and South Korea needs a critical reassessment. In this study, we clarify the taxonomic status of Corbicula species of this area based on a combination of molecular genetic, conchological and anatomical data. According to our results, four Corbicula lineages, corresponding to the nominal species Corbicula japonica , Corbicula elatior , Corbicula leana and Corbicula fluminea , can be delineated in samples collected in the Primorye and Khabarovsk regions of Russia and South Korea. Two species endemic to the Russian Far East (i.e. Corbicula finitima and Corbicula lindholmi) are considered here as junior synonyms of the species C. japonica , which is widely distributed in estuarine habitats around the Japanese Archipelago, Sakhalin Island, southern Kurile Islands, Primorye and Khabarovsk regions, Korean Peninsula and China. Three nominal species described from the Lower Amur basin (Corbicula amurensis , Corbicula nevelskoyi and Corbicula sirotskii) appeared to be synonyms of C. elatior , whose range covers the Korean Peninsula, Primorye and Khabarovsk regions and, perhaps, China. We delineated several colour morphs of C. fluminea and C. japonica. The distinctness between these colour morphs can be attributed to both heritable and environmental factors. [ABSTRACT FROM AUTHOR]

New molecular phylogenies of the chemosymbiotic bivalve family Lucinidae, using 18S rRNA, 28S rRNA and cytochrome b genes, include species from genera not previously analysed. Notable additions from Myrteinae are sequences from Rostrilucina , Solelucina and Taylorina species, species of Ustalucina , Gonimyrtea from Leucosphaerinae and additional species of Ctena , Codakia , Lucinoma and Divalucina from Codakiinae. New sequences of Lucininae include the type species of Parvilucina (P. tenuisculpta), Liralucina , Falsolucinoma , Easmithia , Jallenia , Radiolucina and Cardiolucina as well as samples of Loripes orbiculatus from multiple localities. Five major clades, defined as subfamilies, are recognized: Pegophyseminae, Myrteinae, Leucosphaerinae, Codakiinae and Lucininae. Two branches, Fimbriinae and Monitilorinae, are represented by single species. Pegophyseminae are an extremely long-branched group with a sister-group relationship to Leucosphaerinae, while Codakiinae are a sister clade to the Lucininae. In various gene trees, the position of Myrteinae is unstable in relation to Pegophyseminae + Leucosphaerinae, Monitilorinae and Fimbriinae. The Myrteinae are not well resolved, with an ambiguous correlation of molecular and morphological characters. Codakiinae now include Divalucina cumingi , shown to be related to Lucinoma rather than Divaricella and Divalinga of the Lucininae. Leucosphaerinae are a well-supported clade but morphologically disparate, with the positions of Gonimyrtea and Callucina unresolved. Several molecularly distinct subclades are recognized within the Lucininae, especially the Lucinisca , Loripes and Parvilucina groups. Parvilucina species are paraphyletic with P. tenuisculpta , the type species, distinct from the western Atlantic species. Codakia , Ctena and Pegophysema have pan-tropical distributions with former connections disrupted by vicariant events of the closure of the eastern Tethyan and Central American Seaways. Species of Radiolucina , Pleurolucina and Lucinisca are present on either side of the Isthmus of Panama. A new classification of the 96 living lucinid genera is presented, providing a framework for future studies of systematics, ecology, biogeography and bacterial symbioses. [ABSTRACT FROM AUTHOR]

As efforts to restore coastal habitats accelerate, it is critical that investments are targeted to most effectively mitigate and reverse habitat loss and its impacts on biodiversity. One likely but largely overlooked impediment to effective restoration of habitat-forming organisms is failing to explicitly consider non-habitat-forming animals in restoration planning, implementation, and monitoring. These animals can greatly enhance or degrade ecosystem function, persistence, and resilience. Bivalves, for instance, can reduce sulfide stress in seagrass habitats and increase drought tolerance of saltmarsh vegetation, whereas megaherbivores can detrimentally overgraze seagrass or improve seagrass seed germination, depending on the context. Therefore, understanding when, why, and how to directly manipulate or support animals can enhance coastal restoration outcomes. In support of this expanded restoration approach, we provide a conceptual framework, incorporating lessons from structured decision-making, and describe potential actions that could lead to better restoration outcomes using case studies to illustrate practical approaches. [ABSTRACT FROM AUTHOR]

Mactra veneriformis (Bivalvia: Mactridae) is a bivalve mollusk of major economic importance in China. Decreased natural yields of M. veneriformis have led to an urgent need for genomic resources. To address this problem and the currently limited knowledge of molecular evolution in this genus, we here report a high-quality chromosome-level genome assembly of M. veneriformis. Our approach yielded a 939.32Mb assembled genome with an N50 contig length of 7,977.84 kb. Hi-C scaffolding of the genome resulted in assembly of 19 pseudochromosomes. Repetitive elements made up 51.79% of the genome assembly. A total of 29,315 protein-coding genes (PCGs) were predicted in M. veneriformis. Construction of a genome-level phylogenetic tree demonstrated that M. veneriformis and Ruditapes philippinarum diverged around 231 million years ago (MYA). Inter-species comparisons revealed that 493 gene families have undergone expansion and 449 have undergone contraction in the M. veneriformis genome. Chromosome-based macrosynteny analysis revealed a high degree of synteny between the 19 chromosomes of M. veneriformis and those of Patinopecten yessoensis. These results suggested that M. veneriformis has a similar karyotype to that of P. yessoensis, and that a highly conserved 19-chromosome karyotype was formed in the early differentiation stages of bivalves. In summary, the genomic resources generated in this work serve as a valuable reference for investigating the molecular mechanisms underlying biological functions in M. veneriformis and will facilitate future genetic improvement and disease treatment in this economically important species. Furthermore, the assembled genome greatly improves our understanding of early genomic evolution of the Bivalvia. [ABSTRACT FROM AUTHOR]

Bivalve molluscs have been the focus of behavioral and physiological studies for over a century, due in part to the relative ease with which their traits can be observed. The author reviews historical methods for monitoring behavior and physiology in bivalves, and how modern methods with electronic sensors can allow for a number of parameters to be measured in a variety of conditions using low-cost components and open-source tools. Open-source hardware and software tools can allow researchers to design and build custom monitoring systems to sample organismal processes and the environment, systems that can be tailored to the particular needs of a research program. The ability to leverage shared hardware and software can streamline the development process, providing greater flexibility to researchers looking to expand the number of traits they can measure, the frequency and duration of sampling, and the number of replicate devices they can afford to deploy. [ABSTRACT FROM AUTHOR]

The presence of small black mussels in the upper intertidal zone of estuarine seashores in Southeast Asia is often overlooked, despite their numerical dominance. Here, we clarify their species identities, taxonomy, geographical distributions and genetic relationships. Our molecular results suggest that three closely related species in East and Southeast Asia form a sister clade to Australian and New Zealand Xenostrobus. Given their distinctness, we resurrect the genus Vignadula to distinguish these two clades. Vignadula atrata , first described from Japan and type species of the genus, is confined to north-east Asia, whilst two other Vignadula species occur natively in Southeast Asia. Of these two species, one is found throughout Thailand, Malaysia, Singapore and Java. We show that this species corresponds to Xenostrobus balani and Xenostrobus mangle described from the Malacca Strait, which are genetically indistinguishable and here considered as one and the same species, Vignadula mangle comb. nov. The other species, Vignadula kuraburiensis sp. nov. , described in this study, has so far been found only in south-west Thailand. Members of Vignadula are, in turn, all clearly different from their closest morphological equivalent in Australia, Xenostrobus pulex. A new subfamily Xenostrobinae is proposed to accommodate the two genera Xenostrobus and Vignadula. [ABSTRACT FROM AUTHOR]

The phylogeny of Veneridae has always been controversial. An inappropriate choice of morphological characteristics and loss of critical molecular information will inevitably lead to conflicts between morphological and molecular evolutionary inferences. Phylogenetic relationships in Veneridae, based on both multigene fragments and mitogenomes, were studied, including the redefinition of controversial taxa based on morphological characteristics. Our results support the monophyly of the subfamilies Chioninae, Gemminae, Gouldiinae, Petricolinae and Sunettinae. Callistinae and Pitarinae are considered as valid. The genus Placamen is placed in Dosiniinae, Periglypta in Venerinae, Pelecyora in Pitarinae and Lioconcha and Hyphantosoma in Gouldiinae. Anomalodiscus squamosus is assigned to Timoclea , whereas Marcia hiantina and Marcia japonica are placed in Tapes. In addition, Claudiconcha japonica is removed from Petricolinae, and Gafrarium tumidum is considered valid. Finally, we propose to divide Veneridae into two families: Veneridae s.s. and Meretricidae, constituted by four and 11 subfamilies, respectively. Our study verifies that multigene fragments and mitochondrial genomes are of vital importance in phylogenetic relationships within Veneridae. [ABSTRACT FROM AUTHOR]

Aims: Explore the diversity of culturable actinobacteria isolated from the Pacific oyster Crassostrea gigas with special emphasis on their antimicrobial activity. Methods and Results: For the characterization of the isolated actinobacteria, a polyphasic approach was adopted and thereby phenotypic descriptions, phylogenetic analysis, evaluations of antimicrobial activities and chemical analyses of crude extracts through HPLC and LC‐HRESIMS were performed. Five strains were isolated from C. gigas. The 16S rRNA gene analysis revealed that three of them were taxonomically affiliated to the genus Streptomyces and the other two strains were related to Micromonospora. High inhibition was detected against different test microorganisms such as Candida albicans, Staphylococcus aureus, Bacillus subtilis and Mycobacterium smegmatis. On the basis of the chemical analysis, 11 compounds from the active fractions of the crude extracts were determined, and 8 were related putatively to previously reported compounds. Conclusions: Actinobacteria isolated from C. gigas represent an interesting reservoir of antimicrobial compounds, and further study to uncover the full capacity of this source is encouraged. Significance and Impact: At present, the study of actinobacteria and their antimicrobial potential from uncommon sources as C. gigas is vital to the development of new therapeutic agents to cope with the widespread resistance of human pathogens. [ABSTRACT FROM AUTHOR]

The bivalve families Teredinidae and Xylophagaidae include voracious consumers of wood in shallow-water and deep-water marine environments, respectively. The taxa are sister clades whose members consume wood as food with the aid of intracellular cellulolytic endosymbionts housed in their gills. This combination of adaptations is found in no other group of animals and was likely present in the common ancestor of both families. Despite these commonalities, the two families have followed dramatically different evolutionary paths with respect to anatomy, life history, and distribution. Here, we present 42 new mitochondrial genome sequences from Teredinidae and Xylophagaidae and show that distinct trajectories have also occurred in the evolution and organization of their mitochondrial genomes. Teredinidae display significantly greater rates of amino acid substitution but absolute conservation of protein-coding gene order, whereas Xylophagaidae display significantly less amino acid change but have undergone numerous and diverse changes in genome organization since their divergence from a common ancestor. As with many bivalves, these mitochondrial genomes encode 2 ribosomal RNAs, 12 protein-coding genes, and 22 tRNAs; atp8 was not detected. We further show that their phylogeny, as inferred from amino acid sequences of 12 concatenated mitochondrial protein-coding genes, is largely congruent with those inferred from their nuclear genomes based on 18S and 28S ribosomal RNA sequences. Our results provide a robust phylogenetic framework to explore the tempo and mode of mitochondrial genome evolution and offer directions for future phylogenetic and taxonomic studies of wood-boring bivalves. [ABSTRACT FROM AUTHOR]

The study of the recent colonization of a symbiont and its interaction with host communities in new locations is an opportunity to understand how they interact. The use of isotopic ratios in trophic ecology can provide measurements of a species' isotopic niche, as well as knowledge about how the isotopic niches between symbiont and host species overlap. Stable isotope measurements were used to assess the sources of carbon assimilated by the host species (the bivalves Mytilus galloprovincialis and Scrobicularia plana) and their associated symbiont pea crab Afropinnotheres monodi , which occurs within these bivalves' mantle cavities. The mixing model estimates suggest that all of them assimilate carbon from similar sources, particularly from pseudofaeces and particulate organic matter in this symbiotic system based on filter feeding. The symbiotic species occupy comparable trophic levels and its association seems to be commensal or parasitic depending on the duration of such association. The pea crab A. monodi reflects a sex-specific diet, where males are more generalist than the soft females because the latter's habitat is restricted to the host bivalve. The high isotopic overlap between soft females and M. galloprovincialis may reflect a good commensal relationship with the host. [ABSTRACT FROM AUTHOR]

Ruditapes aspera is a member of the family Veneridae, the venus clams. This species is morphologically similar to other two globally economically important Ruditapes species, R. decussatus and R. philippinarum. Recent phylogenetic studies of Veneridae based on short DNA sequences have suggested that these species may be less closely related than originally thought. Relationships among species of Ruditapes clearly require further critical study. In this article, we show that the mitochondrial (mt) genome of R. aspera exhibits sex-linked heteroplasmy, that is doubly uniparental inheritance (DUI). Mitogenomic comparisons among three Ruditapes species showed that the features and gene arrangements of their mt genomes did not exhibit a high degree of similarity (this agrees with published data on other congeneric species of Veneridae) and that none of these species have a sister-group relationship with either of the other two species. These three species may belong to three different genera, but a fully revised classification will require considerable additional genomic and morphological data from a dense sampling of species and genera. Furthermore, we show that the pattern of relationships in our phylogeny of Ruditapes provides support for the polyphyletic origin of DUI. [ABSTRACT FROM AUTHOR]

Here, we investigate the shell shape variation of some closely related freshwater species of the bivalve genus Corbicula using descriptive (qualitative), geometric morphometric and traditional conchometric approaches. The combination of these different approaches allows for an effective discrimination between the species C. fluminalis, C. fluminea and C. leana , as well as an unidentified Corbicula sp. The roundness of the shell hinge is an important diagnostic feature, as are shell sculpture (ribs), symmetry of the apertural margin, and both position and extension of the umbo. We also identify possible hybrids between C. fluminalis and C. leana , with these showing features intermediate to those of the parent species. We examine variability of shell features of C. leana in selected areas in Europe and compare these results with material from the native range of Japan and Korea. For C. leana , we identify two geographic morphotypes from the native area; within Europe, there is a high morphological diversity of this species with several new forms arising, most probably as a result of hybridization. [ABSTRACT FROM AUTHOR]

Many caridean shrimps live in symbiosis with bivalves, the shrimps finding refuge and food in the mucus in their host's mantle cavity. We report for the first time the presence of Pontonia margarita Verrill, 1869 on both coasts of Baja California Peninsula, Mexico, as a symbiont of the pen shell Pinna rugosa Sowerby, 1835. The symbiont was found in Laguna Ojo de Liebre (LOL), which faces the Pacific Ocean, and in Bahía Concepción (BC), on the eastern coast facing the Gulf of California. A total of 569 specimens of Pinna rugosa were studied, 472 from LOL (104–277 mm shell length (SL)) and 97 from BC (130–234 mm SL). A total of 376 Pontonia margarita individuals were extracted in LOL (19–41 mm total length (TL)) and 41 in BC (20–48 mm TL). The prevalence of Pontonia margarita was 46% in LOL and 28% in BC. The regression analyses for both sexes of Pontonia margarita showed a high correlation between TL and total weight and abdominal length and TL. The data showed a moderate correlation between TL and the length of the major and minor chelae, and TL and length of the minor chela. There was no significant relationship between biometric parameters of the host and the symbiont. The presence of gravid females of Pontonia margarita (52% in LOL and 39% in BC) in shells suggests reproduction during autumn. [ABSTRACT FROM AUTHOR]

The mitochondrial oxidative stress theory of aging suggests that the organelle's decay contributes to the aging phenotype via exacerbated oxidative stress, loss of organ coordination and energetics, cellular integrity, and activity of the mitochondrial electron transfer system (ETS). Recent advances in understanding the structure of the ETS show that the enzymatic complexes responsible for oxidative phosphorylation are arranged in supramolecular structures called supercomplexes that lose organization during aging. Their exact role and universality among organisms are still under debate. Here, we take advantage of marine bivalves as an aging model to compare the structure of the ETS among species ranging from 28 to 507 years in maximal life span. Our results show that regardless of life span, the bivalve ETS is arrayed as a set of supercomplexes. However, bivalve species display varying degrees of ETS supramolecular organization with the highest supercomplex structures found in Arctica islandica, the longest-lived of the bivalve species under study. We discuss this comparative model in light of differences in the nature and stoichiometry of these complexes and highlight the potential link between the complexity of these superstructures and longer life spans. [ABSTRACT FROM AUTHOR]

The class Bivalvia is a highly successful and ancient taxon including ∼25,000 living species. During their long evolutionary history bivalves adapted to a wide range of physicochemical conditions, habitats, biological interactions, and feeding habits. Bivalves can have strikingly different size, and despite their apparently simple body plan, they evolved very different shell shapes, and complex anatomic structures. One of the most striking features of this class of animals is their peculiar mitochondrial biology: some bivalves have facultatively anaerobic mitochondria that allow them to survive prolonged periods of anoxia/hypoxia. Moreover, more than 100 species have now been reported showing the only known evolutionarily stable exception to the strictly maternal inheritance of mitochondria in animals, named doubly uniparental inheritance. Mitochondrial activity is fundamental to eukaryotic life, and thanks to their diversity and uncommon features, bivalves represent a great model system to expand our knowledge about mitochondrial biology, so far limited to a few species. We highlight recent works studying mitochondrial biology in bivalves at either genomic or physiological level. A link between these two approaches is still missing, and we believe that an integrated approach and collaborative relationships are the only possible ways to be successful in such endeavor. [ABSTRACT FROM AUTHOR]

The Unionidae represent an excellent model taxon for unravelling the drivers of freshwater diversity, but, phylogeographic studies on Southeast Asian taxa are hampered by lack of a comprehensive phylogeny and mutation rates for this fauna. We present complete female- (F) and male-type (M) mitogenomes of four genera of the Southeast Asian clade Contradentini+Rectidentini. We calculate substitution rates for the mitogenome, the 13 protein-coding genes, the two ribosomal units and three commonly used fragments (co1, nd1 and 16S) of both F- and M-mtDNA, based on a fossil-calibrated, mitogenomic phylogeny of the Unionidae. Phylogenetic analyses, including an M+F concatenated dataset, consistently recovers a monophyletic Gonideinae. Subfamily-level topology is congruent with that of a previous nuclear genomic study and with patterns in mitochondrial gene order, suggesting Unionidae F-type 2 as a synapomorphy of the Gonideinae. Our phylogeny indicates that the clades Contradentini+Rectidentini and Lamprotulini+Pseudodontini+Gonideini split in the early Cretaceous (~125 Mya), and that the crown group of Contradentini+Rectidentini originated in the late Cretaceous (~79 Mya). Most gonideine tribes originated during the early Palaeogene. Substitution rates were comparable to those previously published for F-type co1 and 16S for certain Unionidae and Margaritiferidae species (pairs). [ABSTRACT FROM AUTHOR]

A recent study published in Genome Biology & Evolution explores the genetic mechanisms underlying aging and extended lifespans by focusing on bivalve molluscs, such as clams, mussels, oysters, and scallops. These marine and freshwater animals have a wide range of lifespans, from 1 year to over 500 years, making them ideal subjects for investigating longevity. The study identified a network of genes that evolve differently in long-lived and short-lived bivalves, many of which are associated with longevity in other animals. The findings suggest a shared molecular framework for extended longevity across diverse animal lineages. This research highlights the importance of studying long-lived nonmodel organisms to gain insights into aging and longevity. [Extracted from the article]

Bivalve molluscs comprise 20,000 species occupying a wide diversity of marine habitats. As filter feeders and detritivores they act as ecosystem engineers clarifying water, creating reefs, and protecting coastlines. The global decline of natural oyster reefs has led to increased restoration efforts in recent years. Bivalves also play an important role in global food security contributing to >20% of worldwide aquaculture production. Despite this importance, relatively little is known about bivalve evolutionary adaptation strategies. Difficulties previously associated with highly heterozygous and repetitive regions of bivalve genomes have been overcome by long-read sequencing, enabling the generation of accurate bivalve assemblies. With these resources we have analyzed the genomes of 32 species representing each molluscan class, including 15 bivalve species, to identify gene families that have undergone expansion during bivalve evolution. Gene family expansions across bivalve genomes occur at the point of evolutionary pressures. We uncovered two key factors that shape bivalve evolutionary history: expansion of bivalvia into environmental niches with high stress followed by later exposure to specific pathogenic pressures. The conserved expansion of protein recycling gene families we found across bivalvia is mirrored by adaptations to a sedentary lifestyle seen in plants. These results reflect the ability of bivalves to tolerate high levels of environmental stress and constant exposure to pathogens as filter feeders. The increasing availability of accurate genome assemblies will provide greater resolution to these analyses allowing further points of evolutionary pressure to become clear in other understudied taxa and potentially different populations of a single species. [ABSTRACT FROM AUTHOR]

The diversity of gastropods and bivalves, total mollusc richness and total mollusc abundance were analysed for three substrates (coral, rock and sand) in the coral and reef ecosystems of the Mexican Tropical Pacific (MTP). Up to 3,828 individuals (70% gastropods and 30% bivalves), belonging to 209 species (146 gastropods and 63 bivalves), were identified; this is one of the most diverse molluscan faunas (2.77 species/m2) associated with reef systems in the MTP. Evaluation of the sampling effort demonstrated that 80% of gastropod species and 93% of bivalve species inhabiting the reef system were recovered. The highest abundance occurred in the coral substrate (1,939 individuals), while the highest species richness was found on the rock substrate (131 species). The analysis showed that the greatest spatial variation in total mollusc, gastropod and bivalve diversity occurred among different substrates within individual localities, with minor differences among assemblages with increasing spatial scale reflecting the relative homogeneity of the molluscan fauna in the study area. While the gastropods Conus nux , Steironepion piperatum and Muricopsis zeteki accounted for differences among different regions, and Vermicularia pellucida eburnea and Bostrycapulus aculeatus accounted for differences among states, the abundances of M. zeteki , B. aculeatus and V. pellucida eburnea were related to differences in diversity at the scale of individual localities. Among bivalves, Leiosolenus aristatus , L. plumula and Gastrochaena ovata accounted for differences between regions, states and localities, respectively. Overall, the study shows that species composition is influenced by both the substrate and the geographical location of assemblages. This indicates that conservation strategies should address preserving habitat heterogeneity at local scales in the study area. [ABSTRACT FROM AUTHOR]

The whelk Neptunea arthritica (Buccinidae) is a common fishery species in Hokkaido, northern Japan. Although ecological information is needed for fisheries management, there is only one paper examining the foraging ecology of this species and it reported that N. arthritica preyed mainly on the invasive mussel Mytilus galloprovincialis. To date, no studies have examined utilization of native prey species by this whelk. Here, we report the findings of a study on the native prey utilization by N. arthritica in an area where M. galloprovincialis is not present. We conducted line transect sampling every month from May 2018 to May 2019 on the western coast of Hakodate Bay, southwestern Hokkaido, Japan. Prey items were composed mostly of gastropods (72%), followed by bivalves (24%) and only a small amount of carrion (<4%). Overlapping spatial distributions were observed among size classes of N. arthritica , while the prey utilization varied with body size. Small individuals (<30 mm in shell height) preyed mainly on the small colloniid gastropod Homalopoma sangarense , while larger individuals (>40 mm) preyed mainly on two tegulid gastropods (Chlorostoma lischkei and Omphalius rusticus) and two venerid bivalves (Protothaca euglypta and Ruditapes philippinarum). There were positive size relationships between whelk body size and prey size for prey categories (Vetigastropoda, Caenogastropoda and Bivalvia) and even for the same prey species (H. sangarense, O. rusticus and P. euglypta). These results suggest that N. arthritica is a predator of mobile gastropods, especially during its early life stage, in areas without the invasive Mediterranean mussel. It is possible that the foraging strategy of N. arthritica may differ quite markedly between areas with and without the invasive mussel. [ABSTRACT FROM AUTHOR]

The global decline of freshwater bivalves (Unionida) has prompted many programmes for their conservation and augmentation, which often include a captive breeding component. One key point to such programmes is the collection, maintenance and use of mussel glochidium larvae, which require attachment to a fish host in a sensitive parasitic stage of their life cycle. Understanding the thermal limits of glochidia can increase knowledge of mussel larval survival and ultimately aid in the development of conservation programmes. Glochidia of the endangered thick-shelled river mussel Unio crassus and the non-native Chinese pond mussel Sinanodonta woodiana were observed for active clamping ability at 5, 15, 17, 20 and 25 °C over the course of a 7-d period. The results from this study confirm that an inverse relationship between water temperature and larval viability can be observed in both species. Additionally, the significantly higher thermal tolerance of S. woodiana indicates that the species exhibits competitive invasive behaviour beginning from the larval stage. These findings also suggest that the collection and transportation of glochidia from genetically important yet distant populations is feasible if the larvae can be maintained at temperatures between 5 and 15 °C. [ABSTRACT FROM AUTHOR]

The objective of this review is to update our previously published checklist of Recent freshwater mussel species and genera (Graf & Cummings, 2007, J. Molluscan Stud. : 291–314) to reflect the new data and research findings that have accumulated over the last decade. The MUSSEL Project Database was developed to synthesize the available taxonomic nomenclature, species ranges and published taxonomic hypotheses on genus–species combinations and synonymy. We have found 4,988 available species-group level nominal species representing 958 valid species in 192 genera worldwide, an increase of 118 species since 2007. The current patterns of species richness are discussed with regard to both taxonomy and geography, as is the general flux in the number of species recognized over time. A checklist is provided herein, with a bibliography to key faunistic and taxonomic references. The full dataset is maintained and updated on the MUSSEL Project Web Site (http://mussel-project.net/). [ABSTRACT FROM AUTHOR]

The noble pen shell Pinna nobilis is a Mediterranean endemic and emblematic giant bivalve. Already considered by the late 20th century to be an endangered species, it is facing a dramatic and rapidly expanding epizooty that has decimated populations since mid-2016. The ecological importance of P. nobilis has prompted important investigations for conservation purposes. Here, we report a first analysis of the whole genome sequencing of this animal. This was performed on an Illumina HiSeq X platform using a single paired-end library of short fragments (2 × 150 bp). The de novo contig assembly had a total size of 584 Mb (96,738 contigs, N50 = 7.6 kb, with 0.4% of ambiguous nucleotides), representing 77.5% of the predicted genome size of 754 Mb. The P. nobilis genome is highly AT-rich, with a GC content of 35.6%. At 1%, heterozygosity was in the range of other bivalves with sequenced genomes. Over one-third (36.2%) of the genome consisted of repeated elements with a surprising larger number of short interspersed nuclear elements compared to other molluscan genomes. We were also able to reconstruct the full mitochondrial genome (c. 19 kb, with 12 protein-coding genes, 2 rRNA and 22 tRNA genes). In the context of the epizootic outbreak affecting P. nobilis , a first insight into the innate immune and stress-related genes found in the sequence is provided. [ABSTRACT FROM AUTHOR]

From a genomics perspective, bivalves (Mollusca: Bivalvia) have been poorly explored with the exception for those of high economic value. The bivalve order Unionida, or freshwater mussels, has been of interest in recent genomic studies due to their unique mitochondrial biology and peculiar life cycle. However, genomic studies have been hindered by the lack of a high-quality reference genome. Here, I present a genome assembly of Potamilus streckersoni using Pacific Bioscience single-molecule real-time long reads and 10X Genomics-linked read sequencing. Further, I use RNA sequencing from multiple tissue types and life stages to annotate the reference genome. The final assembly was far superior to any previously published freshwater mussel genome and was represented by 2,368 scaffolds (2,472 contigs) and 1,776,755,624 bp, with a scaffold N50 of 2,051,244 bp. A high proportion of the assembly was comprised of repetitive elements (51.03%), aligning with genomic characteristics of other bivalves. The functional annotation returned 52,407 gene models (41,065 protein, 11,342 tRNAs), which was concordant with the estimated number of genes in other freshwater mussel species. This genetic resource, along with future studies developing high-quality genome assemblies and annotations, will be integral toward unraveling the genomic bases of ecologically and evolutionarily important traits in this hyper-diverse group. [ABSTRACT FROM AUTHOR]