[Ultrastructural study of Palavascia sphaeromae (Trichomycetes Eccrinales) parasite of the proctodeum of Sphaeroma serratum (Crustacea Isopoda) (author's transl)].

All stages of development of Palavascia sphaeromae parasite of the proctodeum of Sphaeroma serratum, are studied for the first time under the electron microscope. The formation of the holdfast, cell walls and septa is followed. In the coiled apex of the mature thalli, the septa form two catogeries of unisporates sporangia leading to two types of spores. Type 1, a multinucleate spore giving birth in situ to several microthalli. Type 2, a uninucleate at first and then quadrinucleate spore, representing the only propagative elements of the species. This study proves that the Palavasciae are well integrated among the Eccrinales order. It also opens a new discussion concerning the phyletic affinities that can exist between the Eccrinales and the other three orders of Trichomycetes.