Cercozoa
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The Cercozoa are a group of protists, including 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 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.
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.
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.
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. 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
- Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews of the Cambridge Philosophical Society 73: 203-266.
- Cavalier-Smith, T. and Chao, E.E. (2003). "Phylogeny and Classification of Phylum Cercozoa (Protozoa)". Protist 154 (3-4): 341-358.
- Sina M. Adl et al (2005). "The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists". Journal of Eukaryotic Microbiology 52 (5): 399. doi:10.1111/j.1550-7408.2005.00053.x.
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
