Archezoa
Encyclopedia
Archezoa was a kingdom
proposed by Thomas Cavalier-Smith
for eukaryote
s that diverged before the origin of mitochondria
. At various times, the pelobionts and entamoebids (now Archamoebae
), the metamonad
s, 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 Diplomadida and Kingdom Parabasala. These 2 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 Archaezoa have the genetic marker of mitochondria in their nucleus that suggests the 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.
Kingdom (biology)
In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...
proposed by Thomas Cavalier-Smith
Thomas Cavalier-Smith
Professor Thomas Cavalier-Smith , FRS, FRSC, NERC Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford...
for eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s that diverged before the origin of mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
. At various times, the pelobionts and entamoebids (now Archamoebae
Archamoebae
The Archamoebae are a group of Amoebozoa distinguished by the absence of mitochondria. They include genera that are internal parasites or commensals of animals . A few species are human pathogens, causing diseases such as amoebic dysentery...
), the metamonad
Metamonad
The metamonads are a large group of flagellate protozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well...
s, and the Microsporidia
Microsporidia
The microsporidia constitute a phylum of spore-forming unicellular parasites. They were once thought to be protists but are now known to be fungi. Loosely 1500 of the probably more than one million species are named now. Microsporidia are restricted to animal hosts, and all major groups of animals...
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 Diplomadida and Kingdom Parabasala. These 2 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 Archaezoa have the genetic marker of mitochondria in their nucleus that suggests the 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.