Cercozoa

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Cercozoa
Cercomonas sp.jpg
Cercomonas
Scientific classification e
Domain: Eukaryota
(unranked): Diaphoretickes
Kingdom: Chromista
Subkingdom: Harosa
Infrakingdom: Rhizaria
Phylum: Cercozoa
Cavalier-Smith 1998[1]
Groups[4]

The Cercozoa are a group of single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level,[5] being defined by molecular phylogenies of rRNA and actin or polyubiquitin.[6] They are the natural predators of many species of microbacteria and Archea.

Characteristics

The group includes most amoeboids and flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome or mouth as found in many other protozoa. They show a variety of forms[4] and have proven difficult to define in terms of structural characteristics, although their unity is strongly supported by genetic studies. Cercozoa are closely related to Foraminifera and Radiolaria, amoeboids that usually have complex shells, and together with them form a supergroup called the Rhizaria.

Types

They are sometimes grouped by whether they are "filose" or "reticulose".[7]

Filose (subphylum Filosa)

The best-known Cercozoa are the euglyphids, filose amoebae with shells of siliceous scales or plates, which are commonly found in soils, nutrient-rich waters, and on aquatic plants. Some other filose amoebae produce organic shells, including the tectofilosids and Gromia. They were formerly classified with the euglyphids as the Testaceafilosia. This group is not monophyletic, but nearly all studied members fall in or near the Cercozoa, related to similarly shelled flagellates. Other notable filose cercozoans include the cercomonads, which are common soil flagellates.

Reticulose (subphylum Endomyxa)

Another important group placed here are the chlorarachniophytes, strange amoebae that form a reticulating net. They are set apart by the presence of chloroplasts, which apparently developed from an ingested green alga. They are bound by four membranes and still possess a vestigial nucleus, called a nucleomorph. As such, they have been of great interest to researchers studying the endosymbiotic origins of organelles.

Chlorarachniophytes are sometimes considered Filosa, rather than Endomyxa, while groups such as Gromia are considered Endomyxa.[8] Filosa is apparently a monophyletic group, but Endomyxa is paraphyletic.[9]

Ungrouped

In addition, three groups that are traditionally considered heliozoans belong here: the Heliomonadida, Desmothoracida, and Gymnosphaerida, which were recently grouped into the new class of Granofilosea.[7]

Finally, cercozoans include the Phaeodarea, marine protozoa that were previously considered radiolarians.

Classification

Further information: wikispecies:Cercozoa

The exact composition and classification of the Cercozoa are still being worked out. A general scheme is:

Class Chlorarachnea Chlorarachniophyta
Class Proteomyxidea Gymnophryida, Heliomonadida, Desmothoracida, Gymnosphaerida, etc.
Class Sarcomonadea Cercomonadida
Class Imbricatea / Silicofilosea Euglyphida and Thaumatomonadida
Class Thecofilosea Tectofilosida and Cryomonadida
Class Phaeodarea
Class Ebridea Ebridea

In addition two groups of parasites, the Phytomyxea and Ascetosporea, and the shelled amoeba Gromia may be basal Cercozoa, although some trees place them closer to the Foraminifera.

The spongomonads have been included here, but more recently have been considered Amoebozoa.[citation needed]

Some other small groups of protozoans are considered Cercozoa but are of uncertain placement, and it is likely many obscure genera will turn out to be cercozoans with further study.

See also: Auranticordis

Phylogeny

The initial molecular phylogenetic analyses of Cercozoa, based on ribosomal RNA and tubulins, recognized two subphyla, Endomyxa and Filosa, and showed a close relationship with phylum Retaria.[7][10]
However, the monophyly of the group was still uncertain. Posterior phylogenomic analyses consistently recovered Cercozoa as a paraphyletic group, and Endomyxa was often clustered with Retaria.[11][12][13] As a result, the current taxonomy of Rhizaria places Endomyxa inside the phylum Retaria instead of Cercozoa, which has therefore become synonymous with Filosa.[14]

Rhizaria
Filosa
 

Reticulofilosa

 
 

Monadofilosa

 
(=Cercozoa)
Retaria
 

Endomyxa

 
Ectoreta
 

Taxopodida

 
 
 

Foraminifera

 
 

Radiolaria

 
 
 
 
 

Despite the taxonomic change of Endomyxa into phylum Retaria, thanks to better phylogenomic sampling a 2019 analysis recovered phylum Cercozoa as a monophyletic group, with Endomyxa being the sister group to Filosa. In the same analysis, Endomyxa, Filosa, Reticulofilosa and Monadofilosa are proven to be monophyletic too.[15]

Rhizaria
Cercozoa
Filosa
 

Reticulofilosa

 
 

Monadofilosa

 
 
 
 

Endomyxa

 
 

Lapot gusevi

 
 
 
Retaria
 
 

Foraminifera

 
 

Polycystinea

 
 
 

Acantharea

 
 
 

In addition to Endomyxa and Filosa, a variety of clades inside Cercozoa have been discovered in other analyses and have slowly been described and named, such as Tremulida (previously known as Novel Clade 11)[16] and Aquavolonida (Novel Clade 10),[17] although their specific positions among the two main cercozoan subphyla have yet to be refined.

Taxonomy

The taxonomy of Cercozoa as revised in 2018,[18] with Endomyxa shifted into Retaria:

References

  1. ^ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society. 73 (3): 203–266. doi:10.1111/j.1469-185X.1998.tb00030.x. PMID 9809012. S2CID 6557779.
  2. ^ Nikolaev SI, Berney C, Fahrni JF, et al. (May 2004). "The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes". Proc. Natl. Acad. Sci. U.S.A. 101 (21): 8066–71. doi:10.1073/pnas.0308602101. PMC 419558. PMID 15148395.
  3. ^ Hoppenrath, M.; Leander B.S. (2006). "Ebriid phylogeny and the expansion of the Cercozoa". Protist. 157 (3): 279–90. doi:10.1016/j.protis.2006.03.002. PMID 16730229.
  4. ^ a b Cavalier-Smith T, Chao EE (October 2003). "Phylogeny and classification of phylum Cercozoa (Protozoa)" (PDF). Protist. 154 (3–4): 341–58. doi:10.1078/143446103322454112. PMID 14658494.
  5. ^ Chantangsi, C. (2009). Comparative morphology and molecular evolution of marine interstitial cercozoans. PhD thesis. University of British Columbia.
  6. ^ "SYSTEMATIC BIOLOGY: CERCOZOA". Retrieved 2009-03-28.
  7. ^ a b c Bass D, Chao EE, Nikolaev S, et al. (February 2009). "Phylogeny of Novel Naked Filose and Reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea Revised". Protist. 160 (1): 75–109. doi:10.1016/j.protis.2008.07.002. PMID 18952499.
  8. ^ "Cercozoa". Retrieved 2009-05-21.
  9. ^ Nakamura, Yasuhide; Imai, Ichiro; Yamaguchi, Atsushi; Tuji, Akihiro; Not, Fabrice; Suzuki, Noritoshi (2015). "Molecular Phylogeny of the Widely Distributed Marine Protists, Phaeodaria (Rhizaria, Cercozoa)". Protist. 166 (3): 363–373. doi:10.1016/j.protis.2015.05.004. PMID 26083083.
  10. ^ Howe; et al. (2011), "Novel Cultured Protists Identify Deep-branching Environmental DNA Clades of Cercozoa: New Genera Tremula, Micrometopion, Minimassisteria, Nudifila, Peregrinia", Protist, 162 (2): 332–372, doi:10.1016/j.protis.2010.10.002, PMID 21295519
  11. ^ Burki F, Corradi N, Sierra R, Meyer GR, Abbott CL, Keeling PJ, et al. (July 2013). "Phylogenomics of the Intracellular Parasite Mikrocytos mackini Reveals Evidence for a Mitosome in Rhizaria". Current Biology. 23 (16): 1541–1547. doi:10.1016/j.cub.2013.06.033. PMID 23891116. S2CID 8257631.
  12. ^ Burki F, Kudryavtsev A, Matz MV, et al. (2010). "Evolution of Rhizaria: new insights from phylogenomic analysis of uncultivated protists". BMC Evol Biol. 10: 377. doi:10.1186/1471-2148-10-377. PMC 3014934. PMID 21126361.
  13. ^ Krabberød, Anders K.; Orr, Russell J.S.; Bråte, Jon; Kristensen, Tom; Bjørklund, Kjell R.; Shalchian-Tabrizi, Kamran (2017). "Single Cell Transcriptomics, Mega-Phylogeny, and the Genetic Basis of Morphological Innovations in Rhizaria". Mol. Biol. Evol. 34 (7): 1557–1573. doi:10.1093/molbev/msx075. PMC 5455982. PMID 28333264.
  14. ^ Cavalier-Smith, Thomas; E. Chao, Ema; Lewis, Rhodri (2018), "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria", Protoplasma, 255 (5): 1517–1574, doi:10.1007/s00709-018-1241-1, PMC 6133090, PMID 29666938
  15. ^ Irwin, Nicholas A.T.; Tikhonenkov, Denis V.; Hehenberger, Elisabeth; Mylnikov, Alexander P.; Burki, Fabien; Keeling, Patrick J. (2019-01-01). "Phylogenomics supports the monophyly of the Cercozoa". Molecular Phylogenetics and Evolution. 130: 416–423. doi:10.1016/j.ympev.2018.09.004. ISSN 1055-7903. PMID 30318266. S2CID 52982396.
  16. ^ Howe, Alexis T.; Bass, David; Scoble, Josephine M.; Lewis, Rhodri; Vickerman, Keith; Arndt, Hartmut; Cavalier-Smith, Thomas (2011). "Novel Cultured Protists Identify Deep-branching Environmental DNA Clades of Cercozoa: New Genera Tremula, Micrometopion, Minimassisteria, Nudifila, Peregrinia". Protist. 162 (2): 332–372. doi:10.1016/j.protis.2010.10.002. ISSN 1434-4610. PMID 21295519.
  17. ^ Bass D, Tikhonenkov DV, Foster R, Dyal P, Janouškovec J, Keeling PJ, Gardner M, Neuhauser S, Hartikainen H, Mylnikov AP, Berney C (2018). "Rhizarian 'Novel Clade 10' Revealed as Abundant and Diverse Planktonic and Terrestrial Flagellates, including Aquavolon n. gen". Journal of Eukaryotic Microbiology. 65 (6): 828–842. doi:10.1111/jeu.12524. PMC 6282753. PMID 29658156.
  18. ^ Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (April 2018). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria". Protoplasma. 255 (5): 1517–1574. doi:10.1007/s00709-018-1241-1. PMC 6133090. PMID 29666938.

External links

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