Cercozoa

The Cercozoa are a group of protists. They lack shared morphological characteristics at the microscopic level,[5] being defined by molecular phylogenies of rRNA and actin or polyubiquitin.[6]

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[2] 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.

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

Phylogeny based on Bass et al. 2009,[7] Howe etal. 2011[10] and Silar 2016.[11]

Rhizaria

 Phytomyxea 

 Vampyrellida 
Filosa

 Skiomonadea 

 Chlorarachniophyceae 

 Granofilosea 


Monadofilosa

 Metromonadea 

 Cercomonadida 

 Glissomonadida-Sainourida clade 


Ventrifilosa

 Silicofilosea 

 Thecofilosea 


 Reticulosida 

 Gromiidea 

 Ascetosporea 




Retaria

Sticholonchea

Polycystinea

Acantharea

Foraminifera
Cercozoa

Taxonomy

Phylum Cercozoa[10][11][12][13]

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.
  2. 1 2 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.
  3. ↑ 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 419558Freely accessible. PMID 15148395.
  4. ↑ 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.
  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. 1 2 3 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. ↑ Yasuhide Nakamura, Ichiro Imai, Atsushi Yamaguchi, Akihiro Tuji, Fabrice Not, and Noritoshi Suzuki. 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. (See External links below).
  10. 1 2 Howe; et al. (2011), "Novel Cultured Protists Identify Deep-branching Environmental DNA Clades of Cercozoa: New Genera Tremula, Micrometopion, Minimassisteria, Nudifila, Peregrinia", Protist, 162: 332–372, doi:10.1016/j.protis.2010.10.002
  11. 1 2 Silar, Philippe (2016), "Protistes Eucaryotes: Origine, Evolution et Biologie des Microbes Eucaryotes", HAL archives-ouvertes: 1–462
  12. ↑ Adl; et al. (28 September 2012), "The Revised Classification of Eukaryotes" (PDF), Journal of Eukaryotic Microbiology, 59 (5): 429–493, doi:10.1111/j.1550-7408.2012.00644.x
  13. ↑ Ruggiero; et al. (2015), "Higher Level Classification of All Living Organisms", PLoS ONE, 10 (4), doi:10.1371/journal.pone.0119248

External links

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