Light and electron microscope studies on Jirovecia involuta sp. nov. (microspora, bacillidiidae), a new microsporidian parasite of oligochaetes in Sweden.

The new microsporidium Jirovecia involuta is described, based on light and electron microscopy preparations. The host was the oligochaete Limnodrilus hoffmeisteri, collected from a stream in southern Sweden. All developmental stages are diplokaryotic. Mature spores are cylindrical, with a short tail-like projection of exospore material. The spore wall has a uniform exospore. The polaroplast has two regions, anteriorly with closely packed lamellae, posteriorly with tubules. The polar filament has a wide, straight anterior portion, and an approximately equally long, narrow posterior section, forming one coil. Each spore is enclosed in a double-layered sac-like structure, formed by the sporoblast from exospore material. The identity of the species and some traits on the ultrastructural cytology are discussed.