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Cercozoa
Scientific classification
Domain: Eukaryota
Kingdom: Rhizaria
Phylum: Cercozoa
Cavalier-Smith 1998[1]

The Cercozoa are a group of protists. They are sometimes described as a kingdom.[2]

Contents

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[3] 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".[4]

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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.

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.[5]

Ungrouped

Other notable cercozoans include the cercomonads, which are common soil flagellates, and the Phaeodarea, marine protozoa that were previously considered radiolarians. In addition, three groups that are traditionally considered heliozoans belong here: the dimorphids, desmothoracids, and gymnosphaerids.

Classification

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

Class Chlorarachnea chlorarachniophytes
Class Proteomyxidea gymnophryids, dimorphids, desmothoracids, gymnosphaerids, etc.
Class Sarcomonadea cercomonads
Class Imbricatea / Silicofilosea euglyphids and thaumatomonads
Class Thecofilosea tectofilosids and cryomonads
Class Phaeodarea
Class Ebridea ebriids

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.

References

  1. ^ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society 73: 203–266. doi:10.1017/S0006323198005167.  
  2. ^ "CERCOZOAE". http://comenius.susqu.edu/bi/202/RHIZARIA/CERCOZOAE/default.htm. Retrieved 2009-03-28.  
  3. ^ Cavalier-Smith T, Chao EE (October 2003). "Phylogeny and classification of phylum Cercozoa (Protozoa)". Protist 154 (3-4): 341–58. doi:10.1078/143446103322454112. PMID 14658494.  
  4. ^ 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. http://linkinghub.elsevier.com/retrieve/pii/S1434-4610(08)00044-8.  
  5. ^ "Cercozoa". http://tolweb.org/Cercozoa. Retrieved 2009-05-21.  

Wikispecies

Up to date as of January 23, 2010

From Wikispecies

Taxonavigation

Main Page
Cladus: Eukaryota
Supergroup: Rhizaria
Phylum: Cercozoa
Subphyla: Filosa - Endomyxa

References

  • Bass, D.; Chao, E.E.-Y.; Nikolaev, S.; Yabuki, A.; Ishida, K.-i.; Berney, C.; Pakzad, U.; Wylezich, C.; Cavalier-Smith, T. 2008: Phylogeny of novel naked filose and reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea revised. Protist, 160: 75-109.
  • Cavalier-Smith, T.; Chao, E.E.-Y. 2003: Phylogeny and classification of phylum Cercozoa (Protozoa). Protist, 154: 341-358.

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