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Archezoa was a kingdom proposed by Thomas Cavalier-Smith[1][2] for eukaryotes that diverged before the origin of mitochondria. At various times, the pelobionts and entamoebids (now Archamoebae), 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.[3]

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.[by whom?] 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[4] 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.


  1. ^ Tom Cavalier-Smith (May 1989). "Archaebacteria and Archezoa". Nature. 339 (6220): 100–101. doi:10.1038/339100a0. PMID 2497352. 
  2. ^ Tom Cavalier-Smith (December 1993). "Kingdom protozoa and its 18 phyla". Microbiological Reviews. 57 (4): 953–994. PMC 372943Freely accessible. PMID 8302218. 
  3. ^ Poole, Anthony; Penny, David (21 June 2007). "Engulfed by speculation" (PDF). Nature. 447 (7147): 913. doi:10.1038/447913a. PMID 17581566. Retrieved 15 March 2011. 
  4. ^ Germot, Agnès; Philippe, Hervé; Le Guyader, Hervé (1996-12-10). "Presence of a mitochondrial-type 70-kDa heat shock protein in Trichomonas vaginalis suggests a very early mitochondrial endosymbiosis in eukaryotes". Proceedings of the National Academy of Sciences of the United States of America. 93 (25): 14614–14617. doi:10.1073/pnas.93.25.14614. ISSN 0027-8424. PMC 26182Freely accessible. PMID 8962101.