The new microsporidium, Helmichia anomala sp. nov., a parasite of the adipose tissue of the midge larva Microtendipes pedellus (Diptera, Chironomidae) is described, based primarily on ultrastructural characteristics. Each diplokaryotic sporont yields eight monokaryotic sporoblasts in a thin-walled sporophorous vesicle containing tubular and granular inclusions. Sporogonial reproduction is by rosette-like budding. The live spores are rod-shaped measuring 1.3 ± 0.2 (0.9-1.7) x 2.9 ± 0.4 (2.3-4.2) mm. The spore wall consists of a plasmalemma, a thin endospore, and a two layered exospore 30-34 nm wide. The polaroplast has two subdivisions: tightly packed lamellae and a posterior, probably, spongious zone. The uncoiled isofilar polar filament measured 104-109 nm in diameter. A small number of single diplokaryotic spores and anomalous spores are recorded. Discrimination from other microsporidian species and its systematic position are discussed.

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