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The spatial distribution and size structure of two infaunal filter‐feeding bivalves, that is, Sakhalin surf clam Spisula sachalinensis (Schrenck, 1862) and dwarf sunray surf clam Mactra crossei (Dunker, 1877), and an epibenthic deposit feeder, namely the sand dollar Scaphechinus mirabilis (A. Agassiz, 1864), were investigated on an open sandy beach in northern Japan after the tsunami caused by the 2011 Tohoku earthquake. Settlement of S. sachalinensis was relatively abundant in the 2011‐ and 2012‐year classes, but then substantially decreased until the early months of 2013. The 0+‐year‐old distribution was associated mainly with a depth gradient and weakly with the median grain size of the sediment. Mactra crossei had (1) an inverse trend in long‐shore variation in abundance at 2+ years of age and (2) later‐post‐settlement processes that regulated its population dynamics, compared to those of S. sachalinensis. The 2010‐year classes for both Mactridae species survived until 2+ years of age, although their abundance showed a high level of spatial variation. Scaphechinus mirabilis showed fine‐scale spatial variation in their recruitment dynamics. The cross‐shore distribution of S. mirabilis showed a clear ontogenetic shift from shallow to deep water. The cross‐shore distribution of small S. mirabilis (<40 mm in test diameter) overlapped that of the juvenile S. sachalinensis, but their interaction was unclear. Overall, the level of spatial and temporal recruitment variation was relatively high in each species. However, the tsunami has scarcely influenced the cross‐shore distribution and population structure of each species. [ABSTRACT FROM AUTHOR]

Simple Summary: Mitochondrial genomes have become a powerful tool for studying molecular genetics and phylogeny of mollusks. In this study, the complete mitochondrial genome of Mactra grandis was characterized for the first time. The newly sequenced mitochondrial genome fits the typical composition pattern of mollusks with 37 functional genes. Among the Mactridae species with reported mitochondrial genomes, Mactra grandis has the closest relationship with Mactra cygnus. The gene arrangement, genetic distance, and selective pressure of protein-coding genes among Mactra species were also analyzed. This study provides a molecular basis for taxonomy and germplasm research on Mactridae species. Mitochondrial genomes are playing an increasingly important role in molluscan taxonomy, germplasm, and evolution studies. The first complete mitochondrial genome of the commercial big brown mactra clam, Mactra grandis, was characterized using Illumina next-generation sequencing in this study. The 17,289 bp circular genome has a typical gene organization of 13 protein-coding genes (PCGs), 2 rRNAs, and 22 tRNAs, with an obvious (A + T)-bias of 64.54%. All PCGs exhibited a homogeneous bias in nucleotide composition with a (A + T)-bias, a positive GC skew, and a negative AT skew. Results of phylogenetic analysis showed that Mactra grandis was most closely related to Mactra cygnus. The functional gene arrangement of the two species was identical but different from other Mactra species. The congeneric relationships among Mactra species were demonstrated by genetic distance analysis. Additionally, the selective pressure analysis suggested that cox1 was highly efficient for discriminating closely related species in genus Mactra, while nad2 was the most appropriate marker for population genetic analysis. [ABSTRACT FROM AUTHOR]

Mesodesma donacium is a surf clam endemic to the southeast Pacific coast, and it is an important resource species of the sandy beach artisanal fishery in Peru and Chile. Over time, the species has shown high variability in population dynamics (presence and abundance), which has been attributed to overfishing and environmental events. In this study, we assess the phylogeography of seven natural beds of M. donacium (17 to 42° S), to reveal the geographic distribution of the genetic diversity through the analysis of 278 sequences of the mitochondrial gene COI. Sequences of the nuclear genes 18S and 28S were used to evaluate the divergence of COI haplogroups. Two divergent parapatric mitochondrial haplogroups were found, which lacked divergence at nuclear markers (18S and 28S); this mito‐nuclear discordance allows inferring that there is no reproductive isolation of mitochondrial haplogroups. The North haplogroup is the only one present at the northernmost site, while only the South haplogroup was present in Cucao in the south. Between 28° and 32° S, coincident with a coastal biogeographic break at 30° S, both haplogroups are in sympatry. Haplogroups differed in their genetic structure, with the North haplogroup representing a single, highly diverse population and the South haplogroup with genetic differentiation and more restricted genetic diversity and gene flow. The divergence in mitochondrial haplogroups without nuclear divergence suggests a past scenario of geographic isolation in the northern and southern areas, without developing reproductive isolation, followed by secondary contact. Given the phylogeography, genetic information should be considered in restocking and management activities. [ABSTRACT FROM AUTHOR]

This paper reports new occurrence records of two bivalve species, Lutraria impar Reeve, 1854, and Meretrix lusoria (Röding, 1798) from the Odisha coast on the basis of the collection from Bahuda estuary, Ganjam, Odisha. The genus Lutraria Lamarck, 1799, was not yet reported from the State, and the report of Lutraria impar is the first report of the genus from the Odisha coast. These specimens were collected from the sandy seabed near the mouth of the Bahuda estuary in Odisha. [ABSTRACT FROM AUTHOR]

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During the SIBES project, a large-scale monitoring of the marine benthos of the Dutch and western German Wadden Sea, three specimens of the bivalve Mulinia lateralis (Say, 1822) (Bivalvia: Mollusca: Mactridae), a common opportunistic species native in the east coast of North America, were found in August 2017 in the Ems-Dollard estuary. Present records backdate of two months the arrival of this species in Europe and first report it for the German Wadden Sea. Further specimens were then found in 2018, confirming its establishment in the area. An analysis of favourable habitat characteristics for M. lateralis showed that large parts of the Dutch Wadden Sea are a potential suitable habitat for this species. [ABSTRACT FROM AUTHOR]

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The family Mactridae is composed of a diverse group of marine organisms, commonly known as trough shells or surf clams, which illustrate a global distribution. Although this family includes some of the most fished and cultured bivalve species, their chromosomes are poorly studied. In this work, we analyzed the chromosomes of Spisula solida, Spisula subtruncata and Mactra stultorum by means of fluorochrome staining, C-banding and fluorescent in situ hybridization using 28S ribosomal DNA (rDNA), 5S rDNA, H3 histone gene and telomeric probes. All three trough shells presented 2n = 38 chromosomes but different karyotype compositions. As happens in most bivalves, GC-rich regions were limited to the nucleolus organizing regions in Spisula solida. In contrast, many GC-rich heterochromatic bands were detected in both Spisula subtruncata and Mactra stultorum. Although the three trough shells presented single 5S rDNA and H3 histone gene clusters, their chromosomal locations differed. Regarding major rDNA clusters, while Spisula subtruncata presented a single cluster, both Spisula solida and Mactra stultorum showed two. No evidence of intercalary telomeric signals was detected in these species. The molecular cytogenetic characterization of these taxa will contribute to understanding the role played by chromosome changes in the evolution of trough shells. [ABSTRACT FROM AUTHOR]

The occurrence of two mactrid bivalves, Mactra (Mactra) queenslandica E.A. Smith and Heterocardia gibbosula Deshayes, in coastal water of Sidoarjo, East Java, Indonesia is reported here. The two species are examined and illustrated based on the local specimens collected. Previously, the distribution of M. queenslandica was reported only from northern-north-east Australia. This finding revealed that the distribution of this bivalve reaches Indonesian waters. Meanwhile, H. gibbosula is common in south-east Asian waters, however this is the first record for Indonesian waters. This result indicated that more mactrid bivalves could be discovered in Indonesian waters. [ABSTRACT FROM AUTHOR]

Although mitochondrial inheritance in metazoans is typically strictly maternal, doubly uniparental inheritance (DUI) is probably the major exception to this widespread rule. DUI has been found in many species of bivalve molluscs, belonging to several different families. Based on current understanding, the detection of DUI generally relies on the detection of two distinct mitochondrial DNA lineages: a female-transmitted one, that dominates somatic tissues in males and females and eggs, and a male-transmitted one, that dominates the male germline and sperm. When a new species with DUI is identified, novel data are available to make a better inference on the evolution of this phenomenon within the Bivalvia. In this study, mitochondrial heteroplasmy in Pseudocardium sachalinense (Schrenck, 1862) is described. This species belongs to the family of Mactridae, in which DUI has not been previously demonstrated: this finding allowed to upgrade the present knowledge about the distribution of DUI. [ABSTRACT FROM AUTHOR]

Copyright of Paläontologische Zeitschrift is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article presents a study on the effect of stocking density and type of diet on the growth and survival of post-larvae of the taquilla clam Mulinia edulis as a contribution to the development of technology for the commercial cultivation of this species. Three monospecific diets and two mixed diets were provided at a fixed total ration of 100,000 cell millilliter (ml) -1;. It was found that postlarvae fed with Isochrysis galbana had the greatest valve length.

The phenotypic shell shape variation of Mactra isabelleana was tested using the geometric morphometric method. Four localities were sampled along the Río de la Plata estuary and the coast of Buenos Aires province. Principal component analysis and canonical variates analysis of the first principal components were performed to reveal the shell variation and differences among localities, respectively. The specimens from different microhabitats mostly overlapped, although differences in shape were observed in the development of the umbo, the enlargement of the dorsoventral axes and the elongation of the posterior end. The ecological and physical parameters that could influence shell shape variation are discussed. [ABSTRACT FROM PUBLISHER]

Coelomactra antiquatais a famous delicacy and a promising new candidate for aquaculture, which belongs to the family Mactridae (Mollusca: Veneroida). The complete mitochondrial genome ofC. antiquata(Liao Ning province, in China, LN) was finished, which is the first representative from this province. The results showed that the total length of LN-mtDNA sequence is 16,797 bp and the content of A + T is 65.01%. It encodes 35 genes, including 12 protein-coding genes, 21 transfer RNA genes and two ribosomal RNA genes. All coding genes are encoded on the heavy strand. Compared with the typical gene content of animal mitochondrial genomes,atp8andtrnSer(UCN)genes are missing in the mitochondrial genome. The complete mitochondrial genome contains 26 non-coding regions (1598 bp), one major non-coding region consists of 1046 bp in which 4.9 tandem repeat sequences (99bp per sequence) was observed. The phylogenetic tree showed that Liaoning population was clustered into one clade with Shandong (Rizhao, Jiaonan and Jimo) and Guangxi (Beihai) populations, meanwhile all of them are far from the Fujian populations (Pingtan, Zhangzhou and Changle). So, Liaoning, Shandong and Guangxi populations have a close relationship. Actually, Fujian is located between Liaoning, Shandong and Guangxi. So, the result challenges the previously assumed relevance between geographic distance and genetic distance. The genetic distance of LiaoningC. antiquataand Fujian (Changle, Zhangzhou and Pingtan)C. antiquata(0.176–0.177) is greater than the genetic distance betweenMytilus galloprovincialisandMytilus trossulus(0.160). The genetic difference of Liaoning population and Fujian populations has reached species level. [ABSTRACT FROM PUBLISHER]

Mactra veneriformis (Bivalvia: Mactridae) is one commonly cultured bivalve species in the western Pacific Ocean. In the current study, the complete mitrochondrial DNA (mtDNA) of the clam M. veneriformis was determined. The M. veneriformis mt genome is 16,854 bp in length and encodes 34 genes on the same strand, including 12 protein-coding genes (PCGs), 2 ribosomal RNA genes and 20 transfer RNA genes. The length of 12 PCGs is 11,358 bp, which accounts for 67.4% in whole mt genome. The proportion is similar to other clams' mt genomes and within those of bivalves mt genomes. Gene order (which is the same as that of RZ C. antiquata) of M. veneriformis mt genome is compared with that of other veneroids. Compared with the typical gene content of animal mt genomes, atp8 and two tRNA Ser genes are missing in the mt genome. All non-coding regions are 1978 bp in length, among them the longest one is speculated as the control region, which is located between the tRNA His and tRNA Arg. The secondary largest non-coding region (NCR664) between the tRNA Gln and tRNA Thr in the M. veneriformis mt genome contains one section of tandem repeats (125 nt × 5.2 or 249 nt ×  2.6). The tandem repeats account for 97.89% (650/664) of the NCR664, which is a unique characteristic of the M. veneriformis mt non-coding regions compared with those of other veneroids. [ABSTRACT FROM AUTHOR]

The snout otter clamLutraria maximaJonas (Veneroida: Mactridae) is an economically important species in the marine bivalves fishery and aquaculture in China. However, the genetic information of this species remains unavailable. In this study, we report the complete mitochondrial genome sequence ofL. maxima. The mitogenome has 17,082 base pairs (63.9% A + T content) and made up of a total of 37 genes (13 protein-coding, 22 transfer RNAs and two ribosomal RNAs), and a 1045 bp non-coding control region. The presence of a gene coding for ATPase subunit 8 was also noted. However, as expected in Mactridae, the gene arrangements showed variations with that of the related species. This study adds to the repository of available mitogenomes of various Mactridae and will provide useful genetic information for future fishery management and aquaculture development of Mactridae. [ABSTRACT FROM PUBLISHER]

The complete mitochondrial genome ofCoelomactra antiquata(Guangxi, in China, GX) was determined. It is 16 801 bp in length and is the first representative from this province. The mitochondrial genome encodes 35 genes, including 12 PCGs, two ribosomal RNA, and 21 transfer RNA genes.Atp8andtrnSer(UCN)genes are missing, compared with the typical gene content of animal mitochondrial genomes. Three (cob, nad1, nad4,andnad6) of the 12 PCGs in the mitochondrial genome initiate with the ATA, while other PCGs start with ATG. Two PCGs (atp6andnad4L) end with incomplete stop codons (T–), and the remaining ones have complete stop codons (TAA or TAG). The largest non-coding region of theC. antiquata(GX) contains one section of tandem repeats (5 × 99 bp). Among all PCGs and rRNAs, thenad5gene contains the maximum polymorphic sites (430), followed bynad4(261) andcox2(240). Two ribosomal RNA genes (srRNAandlrRNA) andcox1are most conservative. The proportions of polymorphic sites in six genes (nad4, nad2, nad6, nad5, cox2,andnad3) are more than 20% (ranging from 20.25% to 25.21%). These high variable genes can be used as molecular markers in the population genetic analysis of the species. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome of the commercially important snout otter clamLutraria rhynchaenawas obtained from low-coverage shotgun sequencing data on the MiSeq platform. TheL. rhynchaenamitogenome has 16,927 base pairs (69% A + T content) and made up of 12 protein-coding genes, 2 ribosomal subunit genes, 22 transfer RNAs, and a 953 bp non-coding AT-rich region. This is the first mitogenome to be sequenced from the genusLutraria,and the seventh to be reported for the family Mactridae. [ABSTRACT FROM AUTHOR]

Post‐settlement dispersal is a key process in the recruitment of bivalves. To assess the role of such secondary migrations and to identify potential associated triggers, we conducted an in situ sampling survey during the summer recruitment period on the bivalve assemblages of a coarse‐sediment temperate tidal habitat in the Chausey archipelago (Normandy, France). The dynamics of drifters were studied using three types of settler traps (for example, bedload, pelagic, and sinking transports), and we monitored both the abiotic (hydrological and hydrodynamic conditions) and the trophic (nano‐ and pico‐sized particulate organic matter [POM]; fatty acid composition of POM and sediment organic matter [SOM]) environmental parameters. Such an approach allows the discrimination of passive migration (due to sediment erosion by tidal currents and waves) from active migration (related to recruit behavior). Secondary migrations were observed in 25 bivalve taxa, and these mainly involved decreasing abundances of Mytilidae, Nuculidae, Semelidae, Mactridae, and Lucinidae individuals on the study site, highlighting the crucial role of these processes in highly dynamic coastal benthic assemblages. Surprisingly, the intense post‐settlement dispersal observed at the end of the recruitment season was not synchronized with periods of high hydrodynamic stress but to a change in the structure of phytoplanktonic assemblages, particularly the nanoeukaryotic component. Such a response by bivalve recruits to a trophic pelagic cue—triggering secondary migrations—could result from an increased demand for energy required for active migratory behavior. [ABSTRACT FROM AUTHOR]

Live specimens of the gulf wedge clam (Rangia cuneata) were for the first time found in the Polish part of the Vistula Lagoon in 2011. The species is native to the Gulf of Mexico and the Atlantic coast of North America. First records of its introduction in Europe were reported in 2005 from Belgium and then in 2010 from the Russian part of the Vistula Lagoon. [ABSTRACT FROM AUTHOR]

We report the first record of Eastonia rugosa in Sardinia. Living individuals and loose valves were found in proximity of the Rio Padrongianus delta, near Olbia in the north-eastern part of the island. Several alien species were found in the same area. It cannot be excluded that E. rugosa reached this locality by anthropogenic media, but the drivers (natural versus anthropogenic) of the range extension of this species still have to be clearly identified. This issue is very important to understand to what extent E. rugosa is adequate as a descriptor of the Mediterranean Sea ‘tropicalization' as suggested in recent monitoring programmes. [ABSTRACT FROM AUTHOR]