Amorphea are members of a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta, 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 fr ...

Animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

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 that the ISP authors and other scientists later rejected. It includes amoebozoa, opisthokonts, and possibly

Apusozoa The Apusozoa are an Obazoa phylum comprising several genera of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the prese ...

Taxonomic revisions within this group

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

( Apusomonadida and Breviatea), and Varisulca, 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, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

. Apusozoa also appears to be paraphyletic. Varisulca 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 th ...

. 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 and Lobosa. Conosa is divided into the aerobic infraphylum Semiconosia ( Mycetozoa 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 Macromycetozo ...

) 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 s ...

. Lobosa consists entirely of non-flagellated lobose amoebae and has been divided into two classes: Discosea, which have flattened cells, and Tubulinea, 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 (

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

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 fr ...

, and related forms) and Amoebozoa. 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. Bikonts include Archaeplastida (plants and relatives) and SAR supergroup, 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 Hacrob ...

, Haptista, Telonemia and picozoa.

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

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 biomolecu ...

carbamoyl phosphate synthase Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine () or ammonia () and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carb ...

, dihydroorotase, aspartate carbamoyltransferase. 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. 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 modi ...

'', 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 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