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Abstract Polydorid species (Annelida, Spionidae), which inhabit the shells of the commercially important oyster Crassostrea gigas, were investigated along the coast of Normandy, France. Eight species, including five new records for Normandy (Polydora onagawaensis, Polydora websteri, Boccardia pseudonatrix, Boccardia proboscidea, and Boccardiella hamata) and two first records in European waters (P. onagawaensis and B. pseudonatrix), were identified based on morphological, molecular biological, and ecological characteristics. Polydora onagawaensis, which belongs to the Polydora ciliata/websteri complex, was discovered in the shells of wild and suspended cultured oysters, as well as in limestone substrates. In the phylogenetic analysis of mitochondrial COI gene sequences, specimens of P. onagawaensis collected from Normandy were grouped together with specimens from the USA into a single clade and were distinguished from the other three lineages that comprised Japanese and USA specimens. Polydora websteri inhabited shells of suspended cultured oysters. Polydora hoplura, Dipolydora giardi, and Dipolydora sp. were observed in shells from the sandy oyster culture grounds. Boccardiella hamata has been found in wild oyster shells from muddy oyster culture grounds. Boccardia pseudonatrix was observed in the shells of both the wild and cultured oysters. Adult and juvenile Boccardia proboscidea were observed in coralline algae, as well as in suspended cultured oysters. Mud tubes were observed to protrude from the outer surface of the shells, and abnormal black and calcareous deposits were secreted on the inner surface of the shells against polydorid penetration.

It is necessary to monitor shell-associated polydorid worms owing to the risk that they pose to commercially important molluscs. This requires accurate identification, but is often hampered by morphological similarities among species, insufficient type specimens, and abridged species descriptions. Thus morphological characteristics and molecular sequences of the most harmful polydorid species, Polydora uncinata from Japan and Australia and Polydora hoplura from South Africa were compared to determine whether they represent two morphologically similar, but genetically distinct species, or a single species. A wide range of morphological variation (with respect to size, length of caruncle and pigmentation patterns) was observed in each species and population, and their variations largely overlapped and revealed them to be at the intraspecific level of a single species. This was confirmed by gene sequences of nuclear 18S and 28S rRNA that were completely identical for P. uncinata and P. hoplura. The mitochondrial 16S rRNA and cyt b gene analyses also showed no genetic differences between these two species. The tree topology of the mitochondrial cyt b gene did not reflect geographic differences but instead suggests artificial transportation of the species. We recommend the synonymization of P. uncinata with P. hoplura.

Nuclear 18S rRNA gene sequences of oyster shell borers, Polydora websteri, P. calcarea and P. haswelli (Polychaeta: Spionidae), were determined for the first time. A wide range of morphological variation, particularly with regard to pigmentation, is observed among these three species. This variation was characterized at the species level. Black pigmentation pattern on the palps is suggested to be a key characteristic for species determination. Polydora websteri and P. haswelli were sister species. This is the first record of P. calcarea from Japan and Australia and P. haswelli from Japan.

Invasions by shell-boring polychaetes such as Polydora websteri Hartman have resulted in the collapse of oyster aquaculture industries in Australia, New Zealand, and Hawaii. These worms burrow into bivalve shells, creating unsightly mud blisters that are unappealing to consumers and, when nicked during shucking, release mud and detritus that can foul oyster meats. Recent findings of mud blisters on the shells of Pacific oysters ( Crassostrea gigas Thunberg) in Washington State suggest a new spionid polychaete outbreak. To determine the identity of the polychaete causing these blisters, we obtained Pacific oysters from two locations in Puget Sound and examined them for blisters and burrows caused by polychaete worms. Specimens were also obtained from eastern oysters ( Crassostrea virginica Gmelin) collected in New York for morphological and molecular comparison. We compared polychaete morphology to original descriptions, extracted DNA and sequenced mitochondrial (cytochrome c oxidase I [mtCOI]) and nuclear (small subunit 18S rRNA [18S rRNA]) genes to determine a species-level molecular identification for these worms. Our data show that Polydora websteri are present in the mud blisters from oysters grown in Puget Sound, constituting the first confirmed record of this species in Washington State. The presence of this notorious invader could threaten the sustainability of oyster aquaculture in Washington, which currently produces more farmed bivalves than any other US state.

Contrary to the early evidence, which indicated that the mitochondrial architecture in one of the two major annelida clades, Sedentaria, is relatively conserved, a handful of relatively recent studies found evidence that some species exhibit elevated rates of mitochondrial architecture evolution. We sequenced complete mitogenomes belonging to two congeneric shell-boring Spionidae species that cause considerable economic losses in the commercial marine mollusk aquaculture: Polydora brevipalpa and Polydora websteri . The two mitogenomes exhibited very similar architecture. In comparison to other sedentarians, they exhibited some standard features, including all genes encoded on the same strand, uncommon but not unique duplicated trnM gene, as well as a number of unique features. Their comparatively large size (17,673 bp) can be attributed to four non-coding regions larger than 500 bp. We identified an unusually large (putative) overlap of 14 bases between nad2 and cox1 genes in both species. Importantly, the two species exhibited completely rearranged gene orders in comparison to all other available mitogenomes. Along with Serpulidae and Sabellidae, Polydora is the third identified sedentarian lineage that exhibits disproportionally elevated rates of mitogenomic architecture rearrangements. Selection analyses indicate that these three lineages also exhibited relaxed purifying selection pressures.

Considering the pivotal role played by erosive organisms in the marine habitat and the scanty knowledge of this phenomenon in the Mediterranean Sea, the present study aimed to identify the pioneer excavating organisms occurring in the first stages of bioerosion, providing the first estimation of their rate of erosion along the North Adriatic Sea. Bioerosion activity was investigated by deploying sets of limestone panels for a period of 2 years. Moreover, micro-computed tomography was used for the first time to study polychaete erosion, confirming it is a very useful tool for the description of erosion processes. Blocks were placed in the touristic harbor Marina Dorica (Ancona) in July 2017 and periodically collected, the first time after a 6-month period, then bimonthly. Two species of the polychaete genus Polydora were the only boring organisms that settled on the experimental substrates. Erosion rate was estimated by measuring the holes produced by both worm species, and the eroded volumes obtained by resin casts of the holes. Polydora appeared after 6 months of exposure significantly changing its density rates (holes·100 cm−2·month−1) during the exposure, being comparable with densities reported from tropical areas. The erosion rate on the contrary is lower, reaching values of 0.053 g·cm−2·year−1.

With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea ( Magallana ) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri , a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.

Background Patinopecten yessoensis , a large and old molluscan group, has been one of the most important aquaculture shellfish in Asian countries because of its high economic value. However, the aquaculture of the species has recently been seriously affected by the frequent outbreaks of Polydora disease, causing great economic losses. Long non-coding RNAs (lncRNAs) exhibit exhibit crucial effects on diverse biological processes, but still remain poorly studied in scallops, limiting our understanding of the molecular regulatory mechanism of P. yessoensis in response to Polydora infestation. Results In this study, a high-throughput transcriptome analysis was conducted in the mantles of healthy and Polydora -infected P. yessoensis by RNA sequencing. A total of 19,133 lncRNAs with 2,203 known and 16,930 novel were identified. The genomic characterizations of lncRNAs showed shorter sequence and open reading frame (ORF) length, fewer number of exons and lower expression levels in comparison with mRNAs. There were separately 2280 and 1636 differentially expressed mRNAs and lncRNAs (DEGs and DELs) detected in diseased individuals. The target genes of DELs were determined by both co-location and co-expression analyses. Functional enrichment analysis revealed that DEGs involved in melanization and biomineralization were significantly upregulated; further, obviously increased melanin granules were observed in epithelial cells of the edge mantle in diseased scallops by histological and TEM study, indicating the crucial role of melanizaiton and biomineralization in P. yessoensis to resist against Polydora infestation. Moreover, many key genes, such as Tyrs , Frizzled , Wnts , calmodulins , Pifs , perlucin , laccase , shell matrix protein , mucins and chitins , were targeted by DELs. Finally, a core lncRNA-mRNA interactive network involved in melanization and biomineralization was constructed and validated by qRT-PCR. Conclusions This work provides valuable resources for studies of lncRNAs in scallops, and adds a new insight into the molecular regulatory mechanisms of P. yessoensis defending against Polydora infestation, which will contribute to Polydora disease control and breeding of disease-resistant varieties in molluscs.

Genomic selection has been widely used in terrestrial animals but has had limited application in aquaculture due to relatively high genotyping costs. Genomic information has an important role in improving the prediction accuracy of breeding values, especially for traits that are difficult or expensive to measure. The purposes of this study were to (i) further evaluate the use of genomic information to improve prediction accuracies of breeding values from, (ii) compare different prediction methods (BayesA, BayesCπ and GBLUP) on prediction accuracies in our field data, and (iii) investigate the effects of different SNP marker densities on prediction accuracies of traits in the Portuguese oyster (Crassostrea angulata). The traits studied are all of economic importance and included morphometric traits (shell length, shell width, shell depth, shell weight), edibility traits (tenderness, taste, moisture content), and disease traits (Polydora sp. and Marteilioides chungmuensis). A total of 18,849 single nucleotide polymorphisms were obtained from genotyping by sequencing and used to estimate genetic parameters (heritability and genetic correlation) and the prediction accuracy of genomic selection for these traits. Multi-locus mixed model analysis indicated high estimates of heritability for edibility traits; 0.44 for moisture content, 0.59 for taste, and 0.72 for tenderness. The morphometric traits, shell length, shell width, shell depth and shell weight had estimated genomic heritabilities ranging from 0.28 to 0.55. The genomic heritabilities were relatively low for the disease related traits: Polydora sp. prevalence (0.11) and M. chungmuensis (0.10). Genomic correlations between whole weight and other morphometric traits were from moderate to high and positive (0.58–0.90). However, unfavourably positive genomic correlations were observed between whole weight and the disease traits (0.35–0.37). The genomic best linear unbiased prediction method (GBLUP) showed slightly higher accuracy for the traits studied (0.240–0.794) compared with both BayesA and BayesCπ methods but these differences were not significant. In addition, there is a large potential for using low-density SNP markers for genomic selection in this population at a number of 3000 SNPs. Therefore, there is the prospect to improve morphometric, edibility and disease related traits using genomic information in this species.

Shellfish culture, based on ecological and market assessment, is considered a driving force for socio-economic change in ecologically complex coastal systems such as lagoons throughout the Mediterranean area. To diversify fish production, the Pacific oyster Crassostrea gigas was cultured at commercial farms in the Varano Lagoon (SE Italy). The aims of this study were to evaluate through four condition indices (CI, CICG, CIE and AFNOR index), the Polydora index (PI), lipid content, quality and market aspects of oysters reared at two different sites (FO and LA) of the Varano Lagoon, which are characterized by different hydrodynamic conditions. The results of this study highlighted the potential economic benefits associated with sustainable aquaculture development in the Varano Lagoon, proving that the area surrounding the LA site was more suitable for oyster culture, reaching commercial size (60 mm) in a shorter time (6–8 months). Higher growth performance of oysters was observed in the spring, when the nutrient availability positively affected the feeding response of suspension feeders. The opposite was found in winter and in summer, when the decrease in growth could be due to the reduction of nutrient and to the increase of salinity, TSM and ISM. The presence of the mud blister worm (Polydora sp.) during rearing could be a real problem, as it damages oyster market value and threatens serious financial loss to the local farmers.