Electron microscopic study of a new microsporean Microsporidium epithelialis sp n. infecting Tubifex sp (Oligochaeta)

The cytology of a new microsporean parasite Microsporidium epithelialis sp. n. from the intestinal epithelial cells of the freshwater oligochaete Tubi fex sp. (Tubificidae) is described. The microsporean occurred together with an actinosporean of the genus Triactinomyxon, which was found between the epithelial cells. The merogonic and sporogonic stages (mature spores includ ed) of the microsporean parasite are monokaryotic. An individual sporophoro us vesicle surrounds each spore. The fixed and stained spore has an average dimension of 1.9-2.5 x 0.9-1.2 mum. The spores are oval with a characteris tic surface layer, showing ornamentation-like projections, which are in clo se contact to the exospore. A short polar filament forming three to four co ils traverses the polaroplast with two lamellar layers. The ultrastructure and other characteristic features of this microsporean parasite are distinc t from those of the microsporean species described so far from oligochaetes .