Share to: share facebook share twitter share wa share telegram print page

Protist classification

A modern non-hierarchical interpretation of the phylogeny of eukaryotes, including protists
(the gray unlabeled line next to Sar represents Telonemia)

A protist (/ˈproʊtɪst/) is any eukaryotic organism (one with cells containing a nucleus) that is not an animal, plant, or fungus. The protists do not form a natural group, or clade, since they exclude certain eukaryotes with whom they share a common ancestor;[a] but, like algae or invertebrates, the grouping is used for convenience. In some systems of biological classification, such as the popular five-kingdom scheme proposed by Robert Whittaker in 1969, the protists make up a kingdom called Protista, composed of "organisms which are unicellular or unicellular-colonial and which form no tissues".[1][b] In the 21st century, the classification shifted toward a two-kingdom system of protists: Chromista (containing the chromalveolate, rhizarian and hacrobian groups) and Protozoa (containing excavates and all protists more closely related to animals and fungi).[2]

The following groups contain protists. The clade Opisthokonta also contains the animals and the fungi, and the kingdom Archaeplastida also contains algae and plants.

Legend:

* Lack of molecular data.
† Extinct, or exclusively fossil taxon.
? Uncertain position, reserved for above-genus taxa.
(P) Paraphyletic or polyphyletic taxon.
(P?) Potentially paraphyletic or polyphyletic taxon.
(=...) Taxonomic synonym.
(...) Same taxon in a different code of nomenclature.

Amorphea

The supergroup Amorphea contains very diverse heterotrophic organisms, from the macroscopic fungi and animals to the unicellular choanoflagellates and classical amoebae. They frequently exhibit the ability to produce multinucleated cells, a trait considered ancestral to Amorphea. They are also capable of producing pseudopodia, as does the closely related CRuMs clade, forming the clade Podiata.[3]

Amorphea is divided into two clades: Amoebozoa, containing well-known amoebae and slime molds, and Obazoa, containing animals, fungi, and their closest relatives. The relationship between these two clades was initially called 'Unikonta', due to a hypothesis where their common ancestor was a unikont, i.e., a eukaryote with just one flagellum.[4] However, this hypothesis was refuted, as there are bikont amorpheans (e.g., Breviata anathema) and it likely is not an ancestral trait to have a single flagellum.[5][6]

Obazoa

Cladogram of Obazoa based on several analyses.[7][8][9]

The clade Obazoa contains two small groups of flagellates, the breviates and the apusomonads, and the large clade Opisthokonta, which contains animals, fungi, and their closest protist relatives.[10] Under the Cavalier-Smith system, breviates and apusomonads were two classes that composed the phylum Apusozoa,[11] but this taxon is paraphyletic, as apusomonads are more closely related to opisthokonts.[7] The taxonomy of apusomonads was expanded in a 2022 phylogenetic sudy that introduced many new genera.[12]

Opisthokonta

Opisthokonts are divided into two branches: Holozoa (animal-related), containing the ichthyosporeans, pluriformeans, filastereans and choanoflagellates; and Nucletmycea or Holomycota (fungus-related), containing the nucleariids and opisthosporidians. These groups, minus opisthosporidians, were classified as different classes within the paraphyletic phylum Choanozoa in the system of Cavalier-Smith, now obsolete. Instead, Choanozoa is the name used for the clade containing choanoflagellates and animals. Opisthosporidians (aphelids, rozellids and microsporidians) are often studied as protists, but are also considered fungi by protistologists[10] and mycologists alike.[13] Both Holozoa and Nucletmycea have been proposed once as superkingdoms by a group of mycologists who classified nucleariids and fungi as kingdoms, but without any mention of holozoan kingdoms.[14]

Amoebozoa

Cladogram of the major groups of Amoebozoa based on an 824-gene phylogenetic analysis published in 2022.[25]

The phylum Amoebozoa contains around 2,400 species[26] of primarily amoeboid protists.[10] It includes a large portion of the traditional Sarcodina, the taxon uniting all amoebae. In particular, it groups naked and testate lobose amoebae (the traditional Lobosa), as well as the archamoebae and eumycetozoans (slime molds), and a few flagellates.[27] After the general 2019 revisions published by the International Society of Protistologists (ISOP),[10] there have been specific revisions to the classification of eumycetozoans[28] and testate amoebae.[29]

Phylum Amoebozoa Lühe 1913 sensu Cavalier-Smith 1998. Genera incertae sedis: Belonocystis, Boveella, Biomyxa, Corallomyxa, Gibbodiscus, Hartmannia, Malamoeba, Malpighamoeba, Oscillosignum, Pseudothecamoeba, Rhabdamoeba, Schoutedamoeba, Stereomyxa, Subulamoeba, Triaenamoeba, Unda.[10]

Archaeplastida

  • Division Glaucophyta Skuja 1954 (=Glaucocystaceae West 1904, Glaucocystophyta Kies and Kremer 1986, Glaucoplantae Marin & Melkonian in Li et al. 2020). Incertae sedis genera: Archaeopsis, Chalarodora, Glaucocystopsis, Peliaina, Strobilomonas.[48]
  • Phylum Picozoa Seenivasan, Sausen, Medlin & Melkonian 2013 (=picobiliphytes Not et al. 2007) → class Picomonadea Seenivasan, Sausen, Medlin & Melkonian 2013 → order Picomonadida Seenivasan, Sausen, Medlin & Melkonian 2013 → family Picomonadidae Seenivasan, Sausen, Medlin & Melkonian 2013. Sole genus: Picomonas Seenivasan, Sausen, Medlin & Melkonian 2013.[h]
  • Phylum Rhodelphidia Tikhonenkov, Gawryluk, Mylnikov & Keeling 2019 → class Rhodelphidea Tikhonenkov, Gawryluk, Mylnikov & Keeling 2019 → order Rhodelphida Tikhonenkov, Gawryluk, Mylnikov & Keeling 2019 → family Rhodelphidae Tikhonenkov, Gawryluk, Mylnikov & Keeling 2019. Sole genus: Rhodelphis Tikhonenkov, Gawryluk, Mylnikov & Keeling 2019.[50]
  • Division Rhodophyta Wettstein 1901 (=Rhodophyceae Thuret 1855, emend. Rabenhorst 1863, Rhodoplantae Saunders and Hommersand 2004 emend. Adl et al. 2005)

Chloroplastida

Pancryptista

Cladogram of Pancryptista based on 2020 and 2022 analyses.[64][65]

The phylum Cryptista contains heterotrophic and photosynthetic single-celled flagellates. Its classification has undergone many changes through the years, and several conflicting systems and nomenclatures coexist. It was described by Thomas Cavalier-Smith in 1989 to unite two distinct groups of flagellates: the photosynthetic cryptomonads, and the heterotrophic goniomonads (respectively the two classes Cryptomonadea and Cyathomonadea). The name Cryptista was meant to be a synonym of Cryptophyta,[66] the algal division described by the same author in previous years.[67] In 2004, he modified the classification of Cryptista to add two subphyla: Cryptomonada, containing the aforementioned classes (renamed as Cryptophyceae and Goniomonadea respectively), and Leucocrypta, containing the heterotrophic katablepharids.[68] The next year, a separate group of authors proposed a different higher ranking for katablepharids as a phylum Kathablepharida or division Katablepharidophyta, related to but independent from phylum Cryptophyta, with no mention of Cryptista.[69] Between 2013 and 2015, Cavalier-Smith updated the classification once more by describing three new subphyla: Rollomonadia, containing the previous subphyla lowered to superclasses; Palpitia, containing the flagellate Palpitomonas bilix;[70] and Corbihelia, containing picozoans, telonemids, and some heliozoan species (Heliomorpha and Microheliella).[71] Corbihelia did not reach consensus: later analyses and revisions separated telonemids and picozoans as their own clades, and placed Heliomorpha in Cercozoa.[10] However, the addition of Palpitomonas and the monophyly of Rollomonadia have been supported in other analyses.[64]

Cryptista was redefined in the 2019 ISOP revision as the clade containing Palpitomonas, katablepharids, goniomonads and cryptomonads. However, this revision introduced yet another classification system that is contradictory with the previous ones. They proposed a single class Cryptophyceae uniting cryptomonads, goniomonads and katablepharids, and treated cryptomonads as a single order Cryptomonadales,[10] although this does not follow scientific consensus: there are more cryptomonad orders (e.g., Pyrenomonadales, Tetragonidiales) and the name Cryptophyceae was already used for taxa that excluded katablepharids[72] and often excluded goniomonads too.[71] There has not been a new revision since.

Unlike with Heliomorpha, the genus Microheliella was genetically sequenced and its affinities have been resolved. In 2022, it was proposed as the sister group of Cryptista, in a clade known as Pancryptista.[65]

Pancryptista Yazaki et al. 2022

Haptista

Stramenopiles

  • Class Platysulcea Cavalier-Smith 2018 → order Platysulcida Cavalier-Smith 2018 → family Platysulcidae Shiratori, Nakayama & Ishida 2015. Sole genus: Platysulcus Shiratori, Nakayama & Ishida 2015.
  • Family Kaonashiidae Weston, Eglit & Simpson 2023. Sole genus: Kaonashia Weston, Eglit & Simpson 2023.[80]

Bigyra

  • Subphylum Opalozoa Cavalier Smith 1991 emend. 2006
    • Infraphylum Placidozoa Cavalier-Smith 2013
      • Class Placididea Moriya, Nakayama & Inouye 2002 → order Placidida Moriya, Nakayama & Inouye 2002 → family Placididae Moriya, Nakayama & Inouye 2002. Genera: Allegra Rybarski & Arndt 2021; Haloplacidia Rybarski, Nitsche & Arndt 2021; Pendulomonas S.M.Tong 1997; Placidia Moriya, Nakayama & Inouye 2002; Placilonga Rybarski & Arndt 2021; Suigetsumonas Okamura & Kondo 2015; Wobblia Moriya, Nakayama & Inouye 2000.[81]
      • Class Nanomonadea Cavalier-Smith in Cavalier-Smith & Scoble 2013 (=clade MAST-3) → order Uniciliatida Cavalier-Smith in Cavalier-Smith & Scoble 2013
      • Class Opalomonadea Cavalier-Smith 2013 (=clade MAST-12). No described species.
      • Superclass Opalinata Wenyon 1926 emend. Cavalier-Smith 1997
    • Infraphylum Bikosea Cavalier-Smith 2018 (=Bicosoecida Grassé 1926 emend. Karpov 1998) → class Bikosea Cavalier-Smith 1986 as "Bicosoecea" orth. em. 2013. Genera not assigned to families: Bilabrum Schoenle & Arndt in Schoenle et al. 2020;[83] Cafileria Jirsová, Füssy, Richtová, Gruber, & Oborník 2019;[84] Cantina Yubuki et al. 2015.
      • Family Pseudobodonidae? Cavalier-Smith in Cavalier-Smith & Scoble 2013. Sole genus: Pseudobodo Griessmann 1913.[85]
      • Subclass Rictidia Cavalier-Smith in Cavalier-Smith & Scoble 2013 → order Rictida Cavalier-Smith in Cavalier-Smith & Scoble 2013 → family Rictidae Cavalier-Smith in Cavalier-Smith & Scoble 2013. Sole genus: Rictus Yubuki, Leander & Silberman 2010.
      • Subclass BicosidiaICZN/BicosoecophycidaeICN Cavalier-Smith in Cavalier-Smith & Chao 2006
        • Superorder Borokiae Cavalier-Smith in Cavalier-Smith & Chao 2006 → order BorokidaICZN/BorokalesICN Cavalier-Smith in Cavalier-Smith & Chao 2006 → family BorokidaeICZN/BorokaceaeICN Cavalier-Smith in Cavalier-Smith & Chao 2006. Sole genus: Boroka Cavalier-Smith in Cavalier-Smith & Chao 2006.
        • Superorder Cyathobodoniae Cavalier-Smith 1993 emend. 2006. Incertae sedis genus: Halocafeteria Park, Cho & Simpson 2006.[83]
          • Order AnoecidaICZN/AnoecalesICN Cavalier-Smith 1997[k]
            • Family AnoecidaeICZN/AnoecaceaeICN Cavalier-Smith in Cavalier-Smith & Chao 2006. Sole genus: Anoeca Cavalier-Smith in Cavalier-Smith & Chao 2006.
            • Family CaecitellidaeICZN/CaecitellaceaeICN Cavalier-Smith in Cavalier-Smith & Chao 2006. Sole genus: Caecitellus Patterson et al. 1993.
            • Family CafeteriidaeICZN/CafeteriaceaeICN Moestrup 1995. Sole genus: Cafeteria Fenchel & Patterson 1988.
            • Family Symbiomonadaceae Cavalier-Smith in Cavalier-Smith & Chao 2006. Sole genus: Symbiomonas Guillou & Chretiennot-Dinet 1999.
          • Order BicoecidaICZN/BicoecalesICN Grassé 1926
          • Order PseudodendromonadidaICZN/PseudodendromonadalesICN Hibberd 1985 emend. Cavalier-Smith 2006.
            • Family PseudodendromonadidaeICZN/PseudodendromonadaceaeICN Karpov 2000. Genera: Cyathobodo Petersen & Hansen 1961; Pseudodendromonas Bourrelly 1953.
            • Family SiluaniidaeICZN/SiluaniaceaeICN Karpov 1998. Genera: Adriamonas Verhagen, Zölffel, Brugerolle & D.J.Patterson 1994; Siluania Karpov 1998; Otto Harder, Ekelund & Karpov 2014; Regin Harder, Ekelund & Karpov 2014.[86]
            • Family ParamonadidaeICZN/ParamonadaceaeICN Kent 1880. Sole genus: Paramonas Kent 1881.
            • Family NanidaeICZN/NanaceaeICN Cavalier-Smith in Cavalier-Smith & Scoble 2013. Sole genus: Nanum Kim et al. 2010 as "Nanos".
            • Family NeradidaeICZN/NeradaceaeICN Cavalier-Smith in Cavalier-Smith & Chao 2006. Sole genus: Nerada Cavalier-Smith in Cavalier-Smith & Chao 2006.
            • Family FilidaeICZN/FilaceaeICN Cavalier-Smith in Cavalier-Smith & Scoble 2013. Sole genus: Filos Kim et al. 2010.
  • Subphylum Sagenista Cavalier-Smith 1995
    • Class Labyrinthulomycetes Arx 1970 ex Dick 2001 (=Labyrinthulea L.S.Olive 1975 ex Cavalier-Smith 1989, 'phylum' LabyrinthomorphaICZN Page in Levine et al. 1980/LabyrinthulomycotaICN Whittaker 1969)[87]
      • Order Amphitremida (Poche 1913) Gomaa et al. 2013
      • Order Amphifilida Cavalier-Smith in Anderson & Cavalier-Smith 2012 as "Amphifiloidea"
        • Family Amphifilidae Cavalier-Smith in Anderson & Cavalier-Smith 2012. Sole genus: Amphifila Cavalier-Smith in Anderson & Cavalier-Smith 2012.
        • Family Sorodiplophryidae Cavalier-Smith in Anderson & Cavalier-Smith 2012. Genera: Fibrophrys Takahashi, Yoshida, Inouye & Watanabe 2016; Sorodiplophrys Cienkowski 1876.
      • Order OblongichytridaICZN/OblongichytrialesICN Bennett et al. 2017 → family OblongichytriidaeICZN/OblongichytriaceaeICN Cavalier-Smith in Anderson & Cavalier-Smith 2012. Sole genus: Oblongichytrium R.Yokoyama & D.Honda 2006.
      • Order LabyrinthulidaICZN Doffein 1901/LabyrinthulalesICN E.A.Bessey 1950
        • Family AplanochytriidaeICZN/AplanochytriaceaeICN Leander ex Cavalier-Smith in Anderson & Cavalier-Smith 2012. Sole genus: Aplanochytrium Bahnweg & Sparrow 1972 emend. C.A.Leander & D.Porter 2000 (=Labyrinthuloides F.O.Perkins 1973).
        • Family LabyrinthulidaeICZN Cienkowski 1867/LabyrinthulaceaeICN Haeckel 1868. Sole genus: Labyrinthula Cienkowski 1864 (=Chlamydomyxa Archer 1875, Pseudoplasmodium Molisch 1926, Labyrinthodictyon Valkanov 1969, Labyrinthorhiza Chadefaud 1956).
        • Family-level clade "StellarchytriidaeICZN/StellarchytriaceaeICN". Sole genus: Stellarchytrium FioRito & Leander 2016.
      • Order ThraustochytridaICZN/ThraustochytrialesICN Sparrow 1943
    • Class Eogyrea Cavalier-Smith 2013 (=clade MAST-6). Genera not assigned to families: Mastreximonas Lax, Cho & Keeling 2024; Vomastromonas Tikhonenkov, Prokina, Cho & Keeling 2024.[89]

Gyrista

Alveolata

Cladogram of Alveolata, based on a SSU rDNA phylogeny of basal alveolates[112] and a 203-gene phylogeny of apicomplexans and their relatives[113] published in 2023.
  • Colponemida(P) Cavalier-Smith 1993 emend. Adl et al. 2019 (=Protalveolata Cavalier-Smith 1991 emend. 2017. Genera not assigned to families: Neocolponema Gigeroff et al. 2023; Loeffela Gigeroff et al. 2023[112]
    • Phylum[o] Colponemidia Tikhonenkov et al. 2014 → class Colponemea Cavalier-Smith 1993 → order Colponemida Cavalier-Smith 1993 → family Colponemidae Cavalier-Smith & Chao 2004. Sole genus: Colponema Stein 1878.
    • Phylum[o] Acavomonidia Tikhonenkov et al. 2014 → class Acavomonea Tikhonenkov et al. 2014 → order Acavomonida Tikhonenkov et al. 2014 → family Acavomonidae Tikhonenkov et al. 2014. Acavomonas Tikhonenkov et al. 2014.
    • Order Palustrimonadida Cavalier-Smith 2017 → family Palustrimonadidae Cavalier-Smith 2017. Sole genus: Palustrimonas Patterson & Simpson 1996.

Myzozoa