Ultrastructural data of the sporulation stages of the microsporidium Gurleya orchestiae, infecting the muscles of talitrid amphipods Orchestia sp. (Crustacea, Amphipoda), are presented. The developmental stages of the parasite have isolated nuclei. Sporogonial reproduction is by rosette-like budding. Sporophorous vesicles contain 4, seldom 8 spores. The episporontal space contains granules and tubules. Spores are of oval shape, monokaryotic with lamellate bipartite polaroplast, double-layered exospore and isofilar polar filament, turned into 8-9 coils.