[9] These fungal microbes are obligate eukaryotic parasites that use a unique mechanism to infect host cells.

After infection they influence their hosts in various ways and all organs and tissues are invaded, though generally by different species of specialised microsporidia.

In the most advanced cases of parasitism the microsporidium rules the host cell completely and controls its metabolism and reproduction, forming a xenoma.

The spore is protected by a wall, consisting of three layers: In most cases there are two closely associated nuclei, forming a diplokaryon, but sometimes there is only one.

[11] In the gut of the host the spore germinates; it builds up osmotic pressure until its rigid wall ruptures at its thinnest point at the apex.

The posterior vacuole swells, forcing the polar filament to rapidly eject the infectious content into the cytoplasm of the potential host.

Simultaneously the material of the filament is rearranged to form a tube which functions as a hypodermic needle and penetrates the gut epithelium.

Once inside the host cell, a sporoplasm grows, dividing or forming a multinucleate plasmodium, before producing new spores.

Different types of spores may be produced at different stages, probably with different functions including autoinfection (transmission within a single host).

arabiensis, significantly impaired transmission of P. falciparum, had "no overt effect" on the fitness of host mosquitoes, and was transmitted vertically (through inheritance).

The parasitic lifestyle of microsporidia has led to a loss of many mitochondrial and Golgi genes, and even their ribosomal RNAs are reduced in size compared with those of most eukaryotes.

For instance, the genomes of Encephalitozoon romaleae and Trachipleistophora hominis contain genes that derive from animals and bacteria, and some even from fungi.

[28] Phylogeny of Rozellomycota[29][30] Rozellales Mitosporidiaceae Morellosporaceae Paramicrosporidiaceae Nucleophagaceae Chytridiopsida Metchnikovellida Neopereziida Ovavesiculida Amblyosporida Glugeida Nosematida The first described microsporidian genus, Nosema, was initially put by Nägeli in the fungal group Schizomycetes together with some bacteria and yeasts.

Instead, microsporidia are proposed to be highly developed and specialized organisms, which just dispensed functions that are needed no longer, because they are supplied by the host.

Three classes of Microsporidia are proposed by Vossbrinck and Debrunner-Vossbrinck, based on the habitat: Aquasporidia, Marinosporidia and Terresporidia.