Parasitic species belonging to the phylum Microspora (See Classification, Protoctista). Microsporidian species of genus Nosema are parasites of silkworms, honeybees, and Drosophila. A unique characteristic of microsporidians is that the unicellular resting spore contains a coiled hollow tube, the polar filament, which is a specialized product of the Golgi apparatus. During infection, the polar filament turns inside out to form a hollow tube through which the infectious part of the spore is extruded into the new host. While microsporidia lack conventional mitochondria, they have some genes for mitochondrial proteins. On the basis of a reanalysis of the sequence data from their rRNAs, it appears that microsporidia are specialized fungi, and their structural simplicity is now attributed to regressive evolution (q.v.). See Encephilitozoon cuniculi, ribosome.
Subjects: Genetics and Genomics.