The rhipidiaceous fungus Nellymyces megaceros Batko, described in the author's previous study has been again found at the type locality in 1971. Observations carried out on this material in the course of fungus population development, have shown that all of the smooth zoosporangia occuring in the 1970 (type) material had been attacked by a holocarpid biflagenate parasitic fungus, and had their openings slightly modified. In the present study, the author describes he.91thy smooth sporangia of N. megaceros, and zoospores forming within them, he describes the above-mentioned parasitic fungus - Rozellopsis uliginosa sp. nov., erects a hypothesis explaining the specific characters of the life cycle of N. megaceros and populations dynamics in this parasite-host system, and resolves the controversal questions of taxonomy of holocarpic parasitic chytrids and lagenidial fungi. In connection with the latter question. two new genera have been established - Skirgiellia and Skirgiellopsis.