Ultrastructure and Molecular Phylogeny of Mrazekia macrocyclopis sp. n. (Microsporidia, Mrazekiidae), a Microsporidian Parasite of Macrocyclops albidus (Jur.) (Crustacea, Copepoda)

Summary. The ultrastructure and molecular phylogeny of a new microsporidium Mrazekia macrocyclopis sp.n., a parasite of the copepod Macrocyclops albidus (Jur.) in North-West of Russia are described. All stages of its life cycle are diplokaryotic. Fresh spores are rod-shaped and 7.3–10.5 × 1.6–2.3 µm in size. Spore ultrastructure is typical of Mrazekia. The polar tube consists of the anterior clavate manubrium followed by a thin filament arranged in 3.5–4.5 nearly vertical coils. Spores are enclosed in individual sporophorous vesicles. SSU rDNA sequence analysis showed attribution of the new species to a cluster of microsporidia infecting insects (Cystosporogenes, Endoreticulatus), microsrustaceans (Glugoides), vertebrates (Vittaforma) and ciliates (Euplotespora) nested within the clade IV sensu Vossbrinck, Debrunner-Vossbrinck (2005). Mrazekia macrocyclopis is not therefore closely related to Bacillidium vesiculoformis, another microsporidium with rod-shaped spores, and the polyphyletic nature of the family of Mrazekiidae is obvious.