Phylogenetic distance of Thelohania butleri Johnston, Vernick, and Sprague, 1978 (Microsporidia; Thelohaniidae), a parasite of the smooth pink shrimp Pandalus jordani, from its congeners suggests need for major revision of the genus Thelohania Henneguy, 1892.

Thelohania butleri, a microsporidian that causes mortality and commercial losses in the smooth pink shrimp Pandalus jordani, is of taxonomic interest as a species resembling the poorly studied type species, Thelohania giardi, of the large, polyphyletic genus Thelohania. We examined the ultrastructure of T. butleri to confirm its identity and reconstructed phylogenies using ribosomal DNA to find the relationship of T. butleri with other Thelohania species in crayfish and ants. Light and transmission electron microscopy from specimens collected from the type locality, the Pacific coast of Canada, confirmed the identity and demonstrated a development similar to that of T. giardi, involving a series of binary fissions without formation of a plasmodium. Phylogenetic analyses consistently showed T. butleri to be distantly related to other Thelohania species, and closely related to species from marine decapods within a larger fish-parasitic clade. Together, features such as host group and habitat, developmental morphology, and phylogeny suggest T. butleri may be a closer relative to T. giardi than any other Thelohania species represented by DNA data so far, and thus imply species from crayfish and ants may not belong in this genus. Results also confirm that genus Thelohania and family Thelohanidae are in need of revision.

Vairimorpha disparis n. comb. (Microsporidia: Burenellidae): a redescription and taxonomic revision of Thelohania disparis Timofejeva 1956, a microsporidian parasite of the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae).

Investigation of pathogens of populations of the gypsy moth, Lymantria dispar (L.) in Central and Eastern Europe revealed the existence of a microsporidium (Fungi: Microsporidia) of the genus Vairimorpha. The parasite produced three spore morphotypes. Internally infective spores are formed in the gut and adjacent muscle and connective tissue; single diplokaryotic spores and monokaryotic spores grouped by eight in sporophorous vesicles develop in the fat body tissues. The small subunit rDNA gene sequences of various isolates of the Vairimorpha microsporidia, obtained from L. dispar in various habitats in the investigated region, revealed their mutual identity. In phylogenetic analyses, the organism clustered with other L. dispar microsporidia that form only diplokaryotic spores in the sporogony cycle. The octospores of certain microsporidia infecting Lepidoptera that were previously described as Thelohania spp., have recently been shown to be one of the several spore morphotypes produced by species in the genus Vairimorpha. Because the description and drawings of a parasite described as Thelohania disparis by Timofejeva fit the characteristics of Vairimorpha, and all octospore-producing microsporidia collected from L. dispar since 1985 are genetically identical Vairimorpha species, it is believed that the parasite characterized here is identical to T. disparis Timofejeva 1956, and is herein redescribed, characterized, and transferred to the genus Vairimorpha as the new combination Vairimorpha disparis n. comb.