Shell Infestation of the Farmed Pacific Oyster Magallana gigas by the Endolith Bivalve Rocellaria dubia

Oyster shells are substratum for different epibiontic and endobiontic organisms, including pests and parasites. Rocellaria dubia is endolithic and facultative tube-dwelling bivalve, boring in different calcareous substrates, including the shells of bivalves. In 2020, R. dubia was found as endolithic in the shells of the Pacific oyster Magalana gigas, from an oyster farm off the Sacca di Goro lagoon (Emilia-Romagna region, Northern Adriatic Sea, Italy). The purpose of this study was to describe this newly recorded association. Altogether, 136 specimens of R. dubia were found in 15 oysters, photographed under a stereoscope, and their length was measured. Heavily infested oysters hosted tens of R. dubia borers, which were perforating the whole thickness of the oyster valves. The flesh of these oysters was heavily damaged, suggesting parasitic association. R. dubia specimens were categorized into three age classes (0–1, 1–2, and 2–3 years old). M. gigas/R. dubia might be a widespread association, overlooked due to the very scarce research on macrofauna associated with M. gigas. Considering the negative effects of R. dubia endobiosis on oyster fitness, and possible impacts on oyster aquaculture, further research should be conducted in order to elucidate the distribution and ecological characteristics of this parasitic association.

Freshwater Perkinsea: diversity, ecology and genomic information

Studies on freshwater Perkinsea are scarce compared to their marine counterparts; they are therefore not well ecologically characterized. In this study, we investigated the diversity, distribution and ecological role of Perkinsea in freshwater ecosystems. Our approach included (1) the phylogenetic analyses of near full-length SSU and LSU sequences of freshwater Perkinsea, (2) a meta-analysis of public Perkinsea 18S ribosomal RNA gene sequences available from the freshwater environments (25 lakes, 4 rivers), (3) microscopic observations of Perkinsea associated with planktonic communities and (4) single amplified genome analysis. Whereas Perkinsea appear to be rare in river ecosystems (85 reads), they are found in almost all of the lakes studied. However, their diversity does vary considerably between lakes (from 0 to 2 463 Operational Taxonomic Units (OTUs)). Phylogenetic analysis showed that the Parvilucifera/Dinovorax/Snorkelia and Perkinsus/Xcellia/Gadixcellia clades resulted from an initial speciation event. This second clade is further split into well-supported, monophyletic groups, including a clade dominated by freshwater representatives, which is further structured into three distinct subclades: freshwater clade 1, freshwater clade 2 and a freshwater and brackish clade. The Perkinsea Single Amplified Genome (SAG) as well as most of the abundant Operational Taxonomic Units (OTUs) fall into freshwater clade 2. The tyramide signal amplification-fluorescent in situ hybridization method showed an internal association between Perkinsea and the colonial phytoplankton Sphaerocystis. The Single Amplified Genome (SAG) annotation contained 698 genes and gene ontology terms could be assigned to 486 protein-coding genes. Although the number of genes appears to be low (10.6% of the entire gene set assessed by BUSCO), the analysis of the proteome revealed some putative secreted virulence factors. This study showed a large distribution of Perkinsea across lake ecosystems and potential parasitic association with phytoplankton. However, further investigations are needed for a better knowledge on the role of these microorganisms in freshwater ecosystems.

The Rubens morph of Formica exsecta Nylander, 1846 and its separation from Formica fennica Seifert, 2000 (Hymenoptera, Formicidae)

A study of numeric morphology-based alpha-taxonomy (NUMOBAT) considering the species Formicaexsecta Nylander, 1846 and F.fennica Seifert, 2000 was performed in 166 nest samples with 485 worker individuals originating from 117 localities of the Palaearctic west of 59°E. The presence of intraspecific pilosity dimorphism is shown for F.exsecta. The setae-reduced phenotype, termed the Rubens morph, shows a frequency of about 25%, and the more abundant setae-rich phenotype, termed the Normal morph, one of 75%. The frequency of nests containing workers of both phenotypes is 15.5% in 58 samples from Denmark, Sweden, and Finland. Applying the DIMORPH test of Seifert (2016) on this territory, it is demonstrated that the association of Rubens and Normal phenotypes within the same nest cannot be interpreted as parabiosis of independent species (p=0.017) or as temporary (p=0.0004) and permanent (p=0.0001) socially parasitic association, whereas genetically mediated intraspecific dimorphism is most likely (p=0.659, all p data according to Fisher’s exact test). The Rubens morph of F.exsecta is phenotypically most similar to F.fennica but is safely separable by four different forms of exploratory data analyses using nest centroids (NC) as input data: NC-Ward, NC-part.hclust, NC-part.kmeans, and NC-NMDS-k-means. Data on zoogeography and the narrow climate niche indicate that F.fennica is unlikely to occur in Norway.

First record of endoparasitism of Pycnogonida in Hydrozoan polyps (Cnidaria) from the Brazilian coast

Despite the relatively high number of recent studies on Cnidaria off the Brazilian coast, we have observed only two records of parasitism on macromedusae and none on polyps. Endoparasitic associations between Pycnogonida larvae and hydroids have been well known since the early 20th century. Protonymph larvae develop inside the gastrovascular cavity of polyps, typically gastrozooids, which are then called gallzooids. This short communication is an unprecedented record of parasitism on the polyps of Brazilian cnidarian fauna. The parasitic association between Pycnogonida Anoplodactylus stictus and a new hydroid species of Podocoryna has been casually detected on the encrusting communities of experimental polyethylene plates installed at the Paranaguá Yacht Club, Paranaguá, south of Brazil from February 2007 to February 2008. This hydrozoan host is most likely an exotic species because it had not been observed in previous studies of Paranaguá Bay or beaches along the southern coast of Brazil in the previous 20 years. Eighty-eight hydroid colonies were analyzed, of which 19 were parasitized mainly from June to August 2007. Protonymphs were pink-red colored, similar to gallzooids and all other polyps of the colony, thus indicating that they had eaten the hosts' tissues. Up to six protonymphs were observed inside the gallzooids. The gallzooid column was elongated, and the tentacles were atrophied or even absent because of the development of the larvae. Some observations of endoparasitism in two live colonies that were maintained in aquaria until their complete disappearance (one month) are also described in this note.