The Archamoebae are a group of

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...

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 used ...

by eukaryotes. They include genera that are internal

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...

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 fro ...

s of animals (''

Entamoeba ''Entamoeba'' is a genus of Amoebozoa found as internal parasites or commensals of animals. In 1875, Fedor Lösch described the first proven case of amoebic dysentery in St. Petersburg, Russia. He referred to the amoeba he observed microsco ...

'' and ''

Endolimax ''Endolimax'' is a genus of amoebozoa that are found in the intestines of various animals, including the species ''E. nana'' found in humans. Originally thought to be non-pathogenic, studies suggest it can cause intermittent or chronic diarrhea ...

''). A few species are human pathogens, causing diseases such as amoebic

dysentery Dysentery (UK pronunciation: , US: ), 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 ...

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

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

. Most have a single

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

and flagellum, but the giant amoeba '' Pelomyxa'' has many of each.

Description

Archamoebae are a diverse group of

amoeba An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudop ...

e. 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 A mitosome is an organelle found in some unicellular eukaryotic organisms, like in members of the supergroup Excavata. The mitosome was found and named in 1999, and its function has not yet been well characterized. It was termed a ''crypton'' by o ...

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 Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...

, 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 ribos ...

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

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...

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 Entamoebidae is a family of Archamoebae. It includes ''Entamoeba ''Entamoeba'' is a genus of Amoebozoa found as internal parasites or commensals of animals. In 1875, Fedor Lösch described the first proven case of amoebic dysentery in S ...

Chatton 1925 em. Cavalier-Smith 1993 **** Genus †'' Entamoebites'' Poinar & Boucot 2006 **** Genus ''

'' Casagrandi & Barbagallo 1895 ** Order

Pelobiontida The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

Page 1976 em. Cavalier Smith 1987 *** Suborder

Pelomyxina The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

Starobogatov 1980 **** Family

Pelomyxidae The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

Shulze 1877 em. Cavalier-Smith 2016 ***** Genus '' Pelomyxa'' Greeff 1874 ***** Genus '' Mastigella'' Frenzel 1892 *** Suborder

Mastigamoebina The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

(Frenzel 1897) Pánek et al. 2016 **** Family Rhizomastigidae Cavalier-Smith 2013 ***** Genus '' Rhizomastix'' Aléxéieff 1911 **** Family

Mastigamoebidae The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

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 ''

'' Kuenen & Swellengrebel 1917 ***** Genus ''

Iodamoeba ''Iodamoeba buetschlii'' is a species of amoeba. It gets its name from its appearance when stained with iodine. Named for Otto Bütschli by Prowazek in 1912, ''Iodamoeba buetschlii'' is a nonpathogenic parasitic ameba, commonly found in the l ...

'' Dobell 1919 ***** Genus ''

Mastigamoeba ''Mastigamoeba'' is a genus of peolobionts, and treated by some as members of the Archamoebae group of protists. ''Mastigamoeba ''are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage is ...

'' Schulze 1875 Archamoebae ''incertae sedis'' * Genus ''

Endamoeba ''Endamoeba'' is a genus of amoeboids in Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. ...

'' Leidy 1879 * Genus ''

Mastigina ''Mastigamoeba'' is a genus of peolobionts, and treated by some as members of the Archamoebae group of protists. ''Mastigamoeba ''are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage ...

'' Frenzel 1897 * Family

Tricholimacidae The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and '' Endolimax''). A few ...

Cavalier-Smith 2013 ** Genus '' Tricholimax'' Frenzel 1892

References

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