Ultrastructure of the wall of the sporophorous vesicle during sporogony of Pleistophora mirandellae (Protozoa:Microspora).

The wall of the younger sporophorous vesicle (enclosing the sporogogonial plasmodium) of Pleistophora mirandellae Vaney and Conte, 1901 is composed of a membranous labyrinth, about 0.3-0.6 microns high, interwoven with host cell cytoplasm. There is electron-opaque matter within the partitions of the labyrinth. At the onset of plasmotomy, the partitions of the labyrinth become shorter and then possibly due to stretching of the wall and withdrawal of the membranes, the electron-opaque matter is ejected to the lumen side of the wall and the partitions disappear. Only cisterna-like remains of the partitions are observable outside the electron-opaque layer. The thickness of walls in vesicles with ripe spores can be even less than 100 nm.