The Archamoebae are a group of

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s originally thought to have evolved before the acquisition of

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

by eukaryotes. They include genera that are internal

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

s or

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

s of animals ('' Entamoeba'' and '' Endolimax''). A few species are human pathogens, causing diseases such as amoebic

dysentery Dysentery ( , ), historically known as the bloody flux, is a type of gastroenteritis that results in bloody diarrhea. Other symptoms may include fever, abdominal pain, and a feeling of incomplete defecation. Complications may include dehyd ...

. The other genera of archamoebae live in freshwater habitats and are unusual among amoebae in possessing

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. Most have a single nucleus and flagellum, but the giant amoeba '' Pelomyxa'' has many of each.

Description

Archamoebae are a diverse group of amoebae. Many have

for motility, while others do not. They grow in the absence of oxygen, though some can tolerate small amounts. Most described species of Archamoebae either lack mitochondria or are described to have reduced mitosomes.

Habitat

They thrive and live in soil, freshwater, and marine habitats.

History

The group Archamoebae was proposed by

Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...

in 1998 as part of the Archezoa, a newly-proposed group to include eukaryotes that had diverged before acquisition of mitochondria and other common eukaryotic cell features. Early molecular trees based on

rRNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

supported this position, placing several Archamoebae genera as separate groups that diverged from other

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s very early on, suggesting that the absence of mitochondria was a primitive condition. However, soon thereafter genetic remnants of mitochondria were found in various Archamoebae, suggesting that these organisms had diverged after the evolution of mitochondria, but had lost their mitochondria over time, and are more closely related to various amoebae and slime molds.

Phylogeny

The following cladogram summarizes the known relationships between the different families of Archamoebae.

Taxonomy

Infraphylum Archamoebae Cavalier-Smith 1993 stat. nov. 1998 * Class Archamoebea Cavalier-Smith 1983 stat. nov. 2004 ** Order Entamoebida Cavalier-Smith 1993 *** Family Entamoebidae Chatton 1925 em. Cavalier-Smith 1993 **** Genus †'' Entamoebites'' Poinar & Boucot 2006 **** Genus '' Entamoeba'' Casagrandi & Barbagallo 1895 ** Order Pelobiontida Page 1976 em. Cavalier Smith 1987 *** Suborder Pelomyxina Starobogatov 1980 **** Family Pelomyxidae Shulze 1877 em. Cavalier-Smith 2016 ***** Genus '' Pelomyxa'' Greeff 1874 ***** Genus '' Mastigella'' Frenzel 1892 *** Suborder Mastigamoebina (Frenzel 1897) Pánek et al. 2016 **** Family Rhizomastigidae Cavalier-Smith 2013 ***** Genus '' Rhizomastix'' Aléxéieff 1911 **** Family Mastigamoebidae Goldschmidt 1907 ***** ?Genus '' Craigia'' Calkins 1913 ***** ?Genus '' Dobellina'' Bishop & Tate 1940 ***** ?Genus '' Pansporella'' Chatton 1925 ***** ?Genus '' Martineziella'' Hegner & Hewitt 1941 non Chalumeau 1986 ***** ?Genus '' Dinamoeba'' Leidy 1874 non Pascher 1916 ***** Genus '' Endolimax'' Kuenen & Swellengrebel 1917 ***** Genus '' Iodamoeba'' Dobell 1919 ***** Genus '' Mastigamoeba'' Schulze 1875 Archamoebae ''incertae sedis'' * Genus '' Endamoeba'' Leidy 1879 * Genus '' Mastigina'' Frenzel 1897 * Family Tricholimacidae Cavalier-Smith 2013 ** Genus '' Tricholimax'' Frenzel 1892

References

Conosa Infraphyla Taxa named by Thomas Cavalier-Smith {{Amoebozoa-stub