Marssoniella elegans Lemmermann, 1900, a parasite of ovarial tissues of the copepod Cyclops vicinus Uljanin, 1875, was studied as a representative of aquatic-clade microsporidia which form "heteroinfectious spores" (spores not infective to the original host as opposed to "homoinfectious spores" which are infective for the original host) and which thus should require an alternate host. Several structural characters of this microsporidian are similar to those of copepod morphs of microsporidia infecting mosquitoes. However, small subunit ribosomal DNA phylogeny indicates that caddis flies (Insecta, Trichoptera) might be the alternate hosts of Marssoniella. Ultrastructural data obtained are used to redefine the genus Marssoniella Lemmermann, 1900 and its type species Marssoniella elegans.

Institute of Parasitology Academy of Sciences of the Czech Republic Branisovská 31 370 05 Ceské Budĕjovice Czech Republic

Genetic diversity of two Daphnia-infecting microsporidian parasites, based on sequence variation in the internal transcribed spacer region