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Amorphea; Temporal range: Early Ectasian - Present, 1400–0 Ma Pha. Proterozoic Archean Had.
Scientific classification
Domain:	Eukaryota
Clade:	Amorphea; Adl et al., 2012
Subgroups
	Obazoa Breviatea; Apusomonadida; Opisthokonts Holomycota; Holozoa; ; ; Amoebozoa;
Synonyms
	Unikonta nom. nud.; Opimoda Derelle et al., 2015;

Amorphea^[1] is a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta, which includes the Fungi, Animals and the Choanomonada, or Choanoflagellates. The taxonomic affinities of the members of this clade were originally described and proposed by Thomas Cavalier-Smith in 2002.^[2]^[4]

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 ISOP authors and other scientists later rejected.^[1]^[5]

It includes amoebozoa, opisthokonts,^[6]^[7] and Apusomonada.^[8]

Taxonomic revisions within this group

Thomas Cavalier-Smith proposed two new phyla: Sulcozoa, which consists of the subphyla Apusozoa (Apusomonadida and Breviatea), and Varisulca, which includes the subphyla Diphyllatea, Discocelida, Mantamonadidae, Planomonadida and Rigifilida.^[9]

Further work by Cavalier-Smith showed that Sulcozoa is paraphyletic.^[10] Apusozoa also appears to be paraphyletic. Varisulca has been redefined to include planomonads, Mantamonas and Collodictyon. 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) and secondarily anaerobic Archamoebae. 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.^[11]

Clade

The group includes eukaryotic cells that, for the most part, have a single emergent flagellum, or are amoebae with no flagella. The unikonts include opisthokonts (animals, fungi, 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, Haptista, Telonemia and picozoa.

	Holomycota (inc. fungi)

	Holozoa (inc. animals)

1300 mya

1500 mya

Diphoda

	? Metamonada

	Discoba

Diaphoretickes

Cryptista

Archaeplastida

	Rhodophyta (red algae)

	Picozoa

	Glaucophyta
1100 mya
	Viridiplantae (plants)
1000 mya

1600 mya

SAR

550 mya

	Alveolata

	Stramenopiles

Bikonts

2200 mya

One view of the great kingdoms and their stem groups.^[12]^[13]^[14]^[15] The Metamonada are hard to place, being sister possibly to Discoba or to Malawimonada^[15] or being a paraphyletic group external to all other eukaryotes.^[16]

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 nucleotides: carbamoyl phosphate synthase, 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^[2] 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, 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

^ ^a ^b ^c Adl SM, Simpson AG, Lane CE, Lukeš J, Bass D, Bowser SS, Brown MW, Burki F, Dunthorn M, Hampl V, Heiss A, Hoppenrath M, Lara E, Le Gall L, Lynn DH, McManus H, Mitchell EA, Mozley-Stanridge SE, Parfrey LW, Pawlowski J, Rueckert S, Shadwick RS, Schoch CL, Smirnov A, Spiegel FW (September 2012). "The revised classification of eukaryotes". J Eukaryot Microbiol. 59 (5): 429–93. doi:10.1111/j.1550-7408.2012.00644.x. PMC 3483872. PMID 23020233.
^ ^a ^b ^c Cavalier-Smith T (March 2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". Int. J. Syst. Evol. Microbiol. 52 (Pt 2): 297–354. doi:10.1099/00207713-52-2-297. PMID 11931142.
^ Derelle, Romain; Torruella, Guifré; Klimeš, Vladimír; Brinkmann, Henner; Kim, Eunsoo; Vlček, Čestmír; Lang, B. Franz; Eliáš, Marek (17 February 2015). "Bacterial proteins pinpoint a single eukaryotic root". Proceedings of the National Academy of Sciences. 112 (7): E693 – E699. Bibcode:2015PNAS..112E.693D. doi:10.1073/pnas.1420657112. PMC 4343179. PMID 25646484.
^ Cavalier-Smith, Thomas (2003). "Protist phylogeny and the high-level classification of Protozoa". European Journal of Protistology. 39 (4): 338–348. doi:10.1078/0932-4739-00002.
^ Roger AJ, Simpson AG (2009). "Evolution: revisiting the root of the eukaryote tree". Current Biology. 19 (4): R165 – R167. doi:10.1016/j.cub.2008.12.032. PMID 19243692. S2CID 13172971.
^ A Minge M, Silberman JD, Orr RJ, et al. (November 2008). "Evolutionary position of breviate amoebae and the primary eukaryote divergence". Proc. Biol. Sci. 276 (1657): 597–604. doi:10.1098/rspb.2008.1358. PMC 2660946. PMID 19004754.
^ Burki F, Pawlowski J (October 2006). "Monophyly of Rhizaria and multigene phylogeny of unicellular bikonts". Mol. Biol. Evol. 23 (10): 1922–30. doi:10.1093/molbev/msl055. PMID 16829542.
^ Burki, Fabien; Roger, Andrew J.; Brown, Matthew W.; Simpson, Alastair G. B. (2020-01-01). "The New Tree of Eukaryotes". Trends in Ecology & Evolution. 35 (1): 43–55. doi:10.1016/j.tree.2019.08.008. ISSN 0169-5347. PMID 31606140.
^ Cavalier-Smith T (May 2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa". Eur J Protistol. 49 (2): 115–78. doi:10.1016/j.ejop.2012.06.001. PMID 23085100.
^ Cavalier-Smith T, Chao EE, Snell EA, Berney C, Fiore-Donno AM, Lewis R (December 2014). "Multigene eukaryote phylogeny reveals the likely protozoan ancestors of opisthokonts (animals, fungi, choanozoans) and Amoebozoa". Mol Phylogenet Evol. 81: 71–85. doi:10.1016/j.ympev.2014.08.012. PMID 25152275.
^ Cavalier-Smith T, Fiore-Donno AM, Chao E, Kudryavtsev A, Berney C, Snell EA, Lewis R (February 2015). "Multigene phylogeny resolves deep branching of Amoebozoa". Mol Phylogenet Evol. 83: 293–304. doi:10.1016/j.ympev.2014.08.011. PMID 25150787.
^ Brown MW, Heiss AA, Kamikawa R, Inagaki Y, Yabuki A, Tice AK, Shiratori T, Ishida KI, Hashimoto T, Simpson A, Roger A (2018-01-19). "Phylogenomics Places Orphan Protistan Lineages in a Novel Eukaryotic Super-Group". Genome Biology and Evolution. 10 (2): 427–433. doi:10.1093/gbe/evy014. PMC 5793813. PMID 29360967.
^ Schön ME, Zlatogursky VV, Singh RP, et al. (2021). "Picozoa are archaeplastids without plastid". Nature Communications. 12 (1): 6651. bioRxiv 10.1101/2021.04.14.439778. doi:10.1038/s41467-021-26918-0. PMC 8599508. PMID 34789758. S2CID 233328713.
^ Tikhonenkov DV, Mikhailov KV, Gawryluk RM, et al. (December 2022). "Microbial predators form a new supergroup of eukaryotes". Nature. 612 (7941): 714–719. doi:10.1038/s41586-022-05511-5. PMID 36477531. S2CID 254436650.
^ ^a ^b Burki F, Roger AJ, Brown MW, Simpson AG (2020). "The New Tree of Eukaryotes". Trends in Ecology & Evolution. 35 (1). Elsevier BV: 43–55. doi:10.1016/j.tree.2019.08.008. ISSN 0169-5347. PMID 31606140. S2CID 204545629.
^ Al Jewari, Caesar; Baldauf, Sandra L. (28 April 2023). "An excavate root for the eukaryote tree of life". Science Advances. 9 (17): eade4973. Bibcode:2023SciA....9E4973A. doi:10.1126/sciadv.ade4973. ISSN 2375-2548. PMC 10146883. PMID 37115919.