Amorphea are members of a taxonomic supergroup that includes the basal

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. In traditional and currently no longer supported classi ...

and Obazoa. That latter contains the

Opisthokont The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...

a, which includes the

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s and the Choanomonada, or

Choanoflagellate The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates, having a funnel shaped collar of interconne ...

s. The taxonomic affinities of the members of this clade were originally described and 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 2002. The International Society of Protistologists, the recognised body for taxonomy of protozoa, recommended in 2012 that the term Unikont be changed to Amorphea because the name "Unikont" is based on a hypothesized

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

that the ISP authors and other scientists later rejected. It includes

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. In traditional and currently no longer supported classi ...

opisthokont The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...

s, and possibly Apusozoa.

Taxonomic revisions within this group

Cavalier-Smith has proposed two new phyla: Sulcozoa, which consists of the subphyla Apusozoa ( Apusomonadida and

Breviatea ''Breviata anathema'' is a single-celled flagellate amoeboid eukaryote, previously studied under the name ''Mastigamoeba invertens''. The cell lacks mitochondria but has remnant mitochondrial genes, and possesses an organelle believed to be a m ...

), and

Varisulca Varisulca was a proposed basal Podiate taxon. It encompassed several lineages of heterotrophic protists, most notably the ancyromonads (planomonads), collodictyonids (diphylleids), rigifilids (''Rigifila'', ''Micronuclearia'') and mantamonadi ...

, which includes the subphyla Diphyllatea, Discocelida, Mantamonadidae, Planomonadida and Rigifilida. The validity of this proposed taxonomy has yet to be ruled upon by the Society of Protistologists. Further work by Cavalier-Smith has shown that Sulcozoa is

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

. Apusozoa also appears to be paraphyletic.

has been redefined to include planomonads, Mantamonas and

Collodictyon ''Collodictyon'' is a genus of single-celled, omnivorous eukaryotes belonging to the collodictyonids, also known as diphylleids. Due to their mix of cellular components, Collodictyonids do not belong to any well-known kingdom-level grouping of t ...

. A new taxon has been created - Glissodiscea - for the planomonads and Mantamonas. Again, the validity of this revised taxonomy awaits confirmation. Amoebozoa seems to be monophyletic with two major branches:

Conosa Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea ( paraphyletic) and Mycetozoa (polyphyletic). In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromyceto ...

and

Lobosa Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered ''Sapocribrum,'' has slender and threadlike (filose) pseudopodia. ...

. Conosa is divided into the aerobic infraphylum

Semiconosia Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea (paraphyletic) and Mycetozoa (polyphyletic). In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa. ...

(

Mycetozoa Mycetozoa is a polyphyletic grouping of slime molds. It was originally thought to be a monophyletic clade, but recently it was discovered that protostelia are a polyphyletic group within Conosa. Classification It can be divided into dictyoste ...

and

Variosea Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea (paraphyletic) and Mycetozoa (polyphyletic). In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa. ...

) and secondarily anaerobic

Archamoebae 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 sp ...

. Lobosa consists entirely of non-flagellated lobose amoebae and has been divided into two classes:

Discosea Discosea is a class of Amoebozoa, consisting of naked amoebae with a flattened, discoid body shape. Members of the group do not produce tubular or subcylindrical pseudopodia, like amoebae of the class Tubulinea. When a discosean is in motion, ...

, which have flattened cells, and

Tubulinea The Tubulinea are a major grouping of Amoebozoa, including most of the more familiar amoebae genera like ''Amoeba'', '' Arcella'', ''Difflugia'' and '' Hartmannella''. Characteristics During locomotion most Tubulinea have a roughly cylindrical f ...

, which has predominantly tube-shaped pseudopodia.

Clade

The group includes

eukaryotic 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. Bacte ...

cells that, for the most part, have a single emergent

flagellum 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 f ...

, or are amoebae with no flagella. The unikonts include

opisthokonts The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...

(

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, and related forms) and

. By contrast, other well-known eukaryotic groups, which more often have two emergent flagella (although there are many exceptions), are often referred to as

bikonts A bikont ("two flagella") is any of the eukaryote, eukaryotic organisms classified in the group Bikonta. Many single-celled members of the group, and the presumed ancestor, have two flagella. Enzymes Another shared trait of bikonts is the fusio ...

. Bikonts include

Archaeplastida The Archaeplastida (or kingdom Plantae ''sensu lato'' "in a broad sense"; pronounced /ɑːrkɪ'plastɪdə/) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group ...

(plants and relatives) and

SAR supergroup The SAR supergroup, also just SAR or Harosa, is a clade that includes stramenopiles (heterokonts), alveolates, and Rhizaria. The name is an acronym derived from the first letters of each of these clades; it has been alternatively spelled "RAS". T ...

, the

Cryptista Cryptista is a clade of algae-like eukaryotes. It is most likely related to Archaeplastida which includes plants and many algae, within the larger group Diaphoretickes. Although it has sometimes placed along with Haptista in the group Hacrobia, ...

Haptista Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with ''Ancoracysta twista'', forms a sister clade to the SAR+Telonemia supergroup, but it may also be sister t ...

Telonemia Telonemia is a phylum of microscopic eukaryote, single-celled organisms. They were formerly classified as protists until that kingdom fell out of general use, and are suggested to have evolutionary significance in being a possible transitional fo ...

and

picozoa Picozoa, Picobiliphyta, Picobiliphytes, or Biliphytes are protists of a phylum of marine unicellular heterotrophic eukaryotes with a size of less than about 3 micrometers. They were formerly treated as eukaryotic algae and the smallest member of ...

Characteristics

The unikonts have a triple-gene fusion that is lacking in the bikonts. The three genes that are fused together in the unikonts, but not bacteria or bikonts, encode enzymes for synthesis of the

pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other ...

nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...

s: carbamoyl phosphate synthase,

dihydroorotase Dihydroorotase (, ''carbamoylaspartic dehydrase'', ''dihydroorotate hydrolase'') is an enzyme which converts carbamoyl aspartic acid into 4,5-dihydroorotic acid in the biosynthesis of pyrimidines. It forms a multifunctional enzyme with carbamoyl ...

aspartate carbamoyltransferase Aspartate carbamoyltransferase (also known as aspartate transcarbamoylase or ATCase) catalyzes the first step in the pyrimidine biosynthetic pathway (). In '' E. coli'', the enzyme is a multi- subunit protein complex composed of 12 subunits (30 ...

. This must have involved a double fusion, a rare pair of events, supporting the shared ancestry of Opisthokonta and Amoebozoa. Cavalier-Smith originally proposed that unikonts ancestrally had a single flagellum and single

basal body A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor W ...

. This is unlikely, however, as flagellated opisthokonts, as well as some flagellated Amoebozoa, including ''

Breviata ''Breviata anathema'' is a single-celled flagellate amoeboid eukaryote, previously studied under the name ''Mastigamoeba invertens''. The cell lacks mitochondria but has remnant mitochondrial genes, and possesses an organelle believed to be a modif ...

'', actually have two basal bodies, as in typical 'bikonts' (even though only one is flagellated in most unikonts). This paired arrangement can also be seen in the organization of

centrioles In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers (Pinophyta), flowering plants (angiosperms) and most fungi, and are ...

in typical animal cells. In spite of the name of the group, the common ancestor of all 'unikonts' was probably a cell with two basal bodies.

References

External links

* Tree of Life.org {{Taxonbar, from=Q474156, from2=Q964455 Eukaryote unranked clades