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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]

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.

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]

Mulinia lateralis is a native bivalve from the Western Atlantic Ocean, distributed from the Gulf of Saint Lawrence in Canada to Yucatan in Mexico. Based on morphological and genetic data of specimens collected in shrimp farms, in this work, we confirm the presence of M. lateralis in the Gulf of Guayaquil, Ecuador. Presence and its consequences of this invasive bivalve in the region is discussed.

The faunal composition, abundance, distribution, population density and diversity of bivalve species of families Mactridae and Veneridae were investigated from 11 sites along the western coasts of the Gulf of Suez during the period from summer 2017 to summer 2019. A total of 13 bivalve species belonging to 5 subfamilies within 9 genera of the two families were recorded. Family Veneridae was the dominant and represented by 11species (84.62%) compared with only 2 species of family Mactridae represented 15.38% of all recorded species. Mactra olorina (family Mactridae), Gafrarium pectinatum, Callista florida and Circe rugifera (family Veneridae) were the most frequent species at sites II (Kabanon), III (Adabia) and IV (Ain Sokhna) during this study. Site III accommodated all recorded bivalves (13 species), followed by 8 species at site II, decreased to 6, 4, 4 and 3 species at sites IV, V (Monte Galala), XI (Al Azazia – north Ras Gharib) and I (Suez Bay), respectively. A total of 1208 individuals were collected from the study sites, 842 individuals (69.70%) are venerids and 366 individuals (30.30%) are mactrids. The majority of individuals (1179) were collected from sites III, II and IV, which accommodated 599, 546 and 34 individuals, respectively. The values of Simpson's diversity index, Shannon-Weaver index, evenness, and Margalef´s Species richness were calculated at each site. The annual values of these indices averaged 0.42, 1.70, 0.21 and 1.11(site II), 0.30, 2.13, 0.16 and 1.88 (site III) and 0.20, 2.35, 0.39 and 1.42 (site IV), for these indices, respectively. The highest values for Simpson's index of similarity recorded 76.19 % and 71.43 % between site II and both of sites III, and IV, respectively. [ABSTRACT FROM AUTHOR]

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]

Thirteen species of bivalves belong to families Mactridae and Veneridae (Mollusca: Bivalvia) were identified and revised during the present study. These species were collected from 10 sites of the intertidal coastal area along the western coasts of the Suez Gulf during the period from summer 2017 to spring 2018. Family Veneridae dominated Mactridae and was represented by 11 species distributed within 8 genera belonging to 4 subfamilies called Callocardiinae, Circinae, Dosiniinae and Tapetinae. The venerid species comprised Callista florida, Pitar hebraea, Circe corcea, C. rugifera, C. scripta, Circenita callipyga, Gafrarium pectinatum, Dosinia erythraea, D. hepatica, Paphia textile, and Tapes deshayesii. In contrast, family Mactridae had only two species (Mactra lilacea and M. olorina), belong to subfamily Mactrinae. The synonyms, diagnostic characteristics, size, habitats, status, the color of live and dead shells and distribution of the identified species were recorded. The taxonomic position was given provided with a constructed key for identification. [ABSTRACT FROM AUTHOR]

The biology and ecology of Darina solenoides, an abundant bivalve of sandy sediments along Patagonian coasts, is poorly known. Here, we investigated the population dynamics and secondary production of this species in Río Gallegos Estuary (Southern Patagonia, Argentina, 51°35'S, 69°01'W). Sampling was conducted monthly, from April 2014 to June 2015, by collecting 10 samples from the intertidal fringe using a core of 10 cm inner diameter. The sediment was mainly composed of fine and very fine (77.5%) sand; total organic matter content was 1.8%. The average population density was 779.4 ± 56.4 ind m-2 the population was composed of four modal groups. The settlement of a new cohort occurred in April-May each year. The von Bertalanffy growth function was L∞ = 49.4 mm; K = 0.5; the calculated lifespan was 4.2 years. Population somatic production was 80.6 g dry mass m-2 yr-1 and the production-to-biomass (P/B) ratio was 0.96. The observed high production supports the hypothesis that D. solenoides is an important resource for many marine species. [ABSTRACT FROM AUTHOR]

Taxonomy and phylogenetic relationships within the family Mactridae have remained debatable because of the plasticity of morphological characteristics and the lack of accurate molecular data, thereby resulting in abundant synonyms and taxa rearrangements. Mitochondrial genomes (mitogenomes) have been widely used as powerful tools to reconstruct phylogenies of various groups of mollusks; however, they have not been used for studying the phylogeny of mactrids specifically. In the present study, mitogenomes of seven Mactridae species, namely Mactra chinensis , Mactra cygnus , Mactra quadrangularis , Mactra cumingii , Mactrinula dolabrata , Raeta pulchella , and Raeta sp., were sequenced by Illumina high-throughput sequencing, and a comparative mitochondrial genomic analysis was conducted. The newly sequenced mitogenomes were double-stranded circular molecules, with all functional genes encoded on the heavy strand. All the new mactrid mitogenomes had two rRNA genes (12S and 16S), 13 protein-coding genes (PCGs) (atp6 , cox1 , cox2 , cox3 , cytb , nad1 , nad2 , nad3 , nad4 , nad4l , nad5 , nad6 , and atp8), and 22 tRNAs. The mitogenomes showed considerable variation in AT content, GC skew, and AT skew. The results of the phylogenetic analysis confirmed monophyly of the family Mactridae and suggested that genera Mactrinula , Spisula , Rangia , and Mulinia should not be placed under subfamily Mactrinae. Our results supported that potential cryptic species existed in Mactra antiquata. We also proposed subfamily Kymatoxinae should belong to the family Mactridae rather than Anatinellidae and Mactra alta in China should be Mactra cygnus. Additionally, conservation in functional gene arrangement was found in genera Mactra , Raeta , and Lutraria. But gene orders in S. sachalinensis and S. solida were quite different, questioning their congeneric relationship. Our results further suggested that the taxonomy within the family Mactridae requires an integrative revision. • Cryptic species exists in Mactra antiquata. • Subfamily Kymatoxinae belongs to Mactridae rather than Anatinellidae. • Gene atp8 exists in all mactrid mitogenomes. • Genera Mactrinula , Spisula , Rangia , and Mulinia should be moved out from subfamily Mactrinae. • Mactra alta in China should be Mactra cygnus. [ABSTRACT FROM AUTHOR]

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]

A partial sequence of mitochondrial cytochrome c oxidase subunit I (COI) was used as a genetic marker for a genetic diversity and phylogenetic analysis (DNA barcoding) of two Mactridae species, Mactra corallina and Eastonia rugosa , collected from the Tunisian coast. These Mactridae species could be distinguished by DNA barcoding techniques and they will be considered as monophyletic clades with the Neighbor-Joining (NJ) tree. The genetic structure detected that E. rugosa presents three haplotypes with a high frequency of HER1 (0.89). However, M. corralina shared 14 haplotypes. The haplotypic diversity ( H ) was equal to 0.205 and 0.954, respectively, for E. rugosa and M. corallina . While the nucleotide diversity ( π ) was higher for M. corallina ( π = 0.0818), the mismatch distribution showed a unimodal curve for E. rugosa (a recent sudden demographic expansion) and a multimodal distribution for M. corallina (size stability) . [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]

The Chinese surf clam Mactra chinensis Philippi, 1846 is a commercially important marine bivalve belonging to the family Mactridae (Mollusca: Bivalvia). In this study, the M. chinensis mitochondrial genomic features are analyzed. The genome has 34 genes on the same strand, lacking atp8 and both trnS ( trnS 1 and trnS 2 ) as compared with the typical gene content of metazoan mitochondrial genomes. The A + T content of M. chinensis mitochondrial genome is 63.72%, which is slightly lower than that of M. veneriformis (67.59%) and Coelomactra antiquata (64.33% and 64.14% for the samples from Ri Zhao, Shandong Province, and Zhang Zhou, Fujian Province, China, respectively) in the same family. There are 22 NCRs in the M. chinensis mitochondrial genome, accounting for 12.91% of the genome length. The longest NCR (1,075 bp in length) is located between trnT and trnQ . A TRS (127 bp × 8.15) accounts for 96.3% (1,035/1,075) of this NCR. The occurrence of TRS in NCR is shared by the two Mactra mitochondrial genomes, but is not found in the two Coelomactra mitochondrial genomes. A phylogenetic tree constructed based on 12 PCGs of 25 bivalve mitochondrial genomes shows that all seven genera ( Mactra , Coelomactra , Paphia , Meretrix , Solen , Mytilus , and Crassostrea ) constitute monophyletic groups with very high support values. Pairwise genetic distance analyses indicate that the genetic distance of C. antiquata from the two localities is 0.084, which is greater than values between congeneric species, such as those in Mactra , Mytilus , Meretrix, and Crassostrea . The results show that the C. antiquata from the two localities represent cryptic species. [ABSTRACT FROM AUTHOR]

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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]

The Snout Otter Clam, Lutraria philippinarum is a regularly harvested bivalve species for food and also as a source of income in the Philippines. For sustainable supply of this resource in the wild, efficient and effective management strategies are needed, and the evaluation of its reproductive biology and fishery are required. In this study, the reproductive biology and fishery of L. philippinarum in the Philippines were examined monthly from January to December 2010 in North Bais Bay, Manjuyod, Negros Oriental and Philippines. For reproductive biology, otter clams were sampled, and sex ratio (by microscopic observation), size at sexual maturity, shell length (with a vernier caliper), gonad development (by histological examination as resting, developing, mature, spawning and spent) and spawning season were determined. Other information such as water temperature, salinity, pH and dissolved oxygen were also measured. To obtain information on the L. philippinarum fishery, interviews were conducted in Negros Oriental, Bohol, Cebu and Sarangani. A total of 677 snout otter clams were sampled. The study showed that L. philippinarum sex ratio was 1:1.15 and showed no significant difference from 1:1 ratio. Males attained its first sexual maturity at 43mm shell length while the females at 46mm. Histological examination on gonad development indicated that gametogenesis, maturation and spawning season of L. philippinarum occurred throughout the year with two spawning peaks, January and June. Changes in water temperature in North Bais Bay may have influenced the spawning peaks of L. philippinarum. Data on the fishery of L. philippinarum revealed that the Catch Per Unit Effort of L. philippinarum in the Philippines ranged from 0.2kg/hr-man to 1.25kg/hr-man suggesting low shell catch. We recommend that some mature individuals have to be left in the population to allow in situ breeding. [ABSTRACT FROM AUTHOR]

Abstract: Species boundaries of some Mactridae species are difficult to define by morphology due to phenotypic plasticity and morphological convergence. DNA barcoding might provide an effective resolution for the confusion. Here, partial sequences of mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA genes from 36 specimens of 11 species are sequenced to assess whether Mactridae species could be distinguished by DNA barcoding techniques. An evident barcoding gap was detected in the COI analyses, while barcoding gap for 16S was not found. Nevertheless, neighbour-joining and Bayesian trees showed that all species but one (Coelomactra antiquata) fell into reciprocally monophyletic clades with high bootstrap support. Results of sequence divergence and topology in Bayesian inference of phylogenetic tree suggested the occurrence of potential cryptic or sibling species in the C. antiquata group. This study demonstrates the efficacy of species identification in Mactridae species via DNA barcoding. [Copyright &y& Elsevier]

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]