Archezoa was a
kingdom proposed by
eukaryotes that diverged before the origin of
mitochondria. At various times, the
metamonads, and the
Microsporidia were included here. These groups appear near the base of eukaryotic evolution on
rRNA trees. However, all these groups are now known to have developed from mitochondriate ancestors, and trees based on other genes do not support their basal placement. The kingdom Archezoa has therefore been abandoned.
Archaezoa is composed of two kingdoms of protists, Kingdom
Diplomonadida and Kingdom
Parabasalia. These two kingdoms are grouped together because they lack mitochondria. The Archaezoa hypothesis suggests that these two kingdoms originally had mitochondria, but lost them before mitochondria became symbionts of protists. This lineage is believed to be the proof of Eukaryotic Endosymbiosis. Molecular evidence indicates that at least an organism of Archaezoa have the genetic marker of mitochondria in their nucleus that suggests they had and then lost mitochondria
 Both of these kingdoms are parasites, as they have to acquire ATP from some source. An example of these Archaezoans is
Trichomonas vaginalis, a common urinary infection that is transmitted through sexual contact.