The light microscopic and ultrastructural characteristics of a microsporidium provisionally identified as Toxoglugea chironomi (Debaiseux, 1931) Jirovec, 1936, is described. It was isolated from oenocytes and adipose tissue of a midge larva of the genus Dicrotendipes. Merozoites are diplokaryotic. The sporogony produces, by fragmentation, eight monokaryotic spores in a sporophorous vesicle. Mature spores are horse-shoe shaped. The total length is about 5.8-mu-m, the width 0.8-0.9-mu-m, the external height of the curve 2.3-3.5-mu-m, and the external width of the curve 3.5-5.2-mu-m. The polaroplast has lamellar compartments of two types: narrow and closely packed anteriorly, and wider and more loosely arranged posteriorly. The isofilar polar filament is arranged in 8-10 coils in the posterior fourth of the spore. The external nuclear membrane is sometimes continuous with the endoplasmic reticulum. Lamellar and tubular material of exospore construction are present in the episporontal space from the beginning of sporogony. Teratological and normal spores sometimes occur together in the sporophorous vesicle. The identification of the species is discussed and the ultrastructure is compared to Toxoglugea variabilis, the only further species of the genus with known ultrastructural cytology.
