Metchnikovella dobrovolskiji sp. nov. (Microsporidia: Metchnikovellida), a parasite of archigregarines Selenidium pygospionis from the polychaete Pygospio elegans

Summary Spore sacs and free spores of a metchnikovellid were found in several specimens of the archigregarine Selenidium pygospionis isolated from polychaetes Pygospio elegans , collected from the littoral area of the Kandalaksha Gulf of the White Sea. The morphology of spore sacs suggests that this species belongs to the genus Metchnikovella ( sensu Caullery and Mesnil, 1914). The length of the spore sacs varied from 5.6 to 9.2 µm, the width of the spore sacs was 3.3–5 µm, each of them contained up to 12 oval spores. Both spore sacs and free spores were enclosed in vacuoles. The combination of morphological features and host range distinguishes the studied isolate from any known species. Results of the phylogenetic analysis based on the SSU rRNA gene showed that the sequence of this species had a significant difference from all available sequences of metchnikovellids and usually grouped close to the species Metchnikovella incurvata or formed a clade with it. Here we describe the studied isolate as a new species, Metchnikovella dobrovolskiji sp. nov. (Microsporidia: Metchnikovellida).