Cercozoa

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Cercozoa

The Cercozoa are a group of protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s, including most amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
s and flagellate

Flagellate

Flagellates are cell s with one or more whip-like organelles called flagellum. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla....
s that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome

Cytostome

A cytostome or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles....
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

Foraminifera

The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net....
and Radiolaria, amoeboids that usually have complex shells, and together with them form a supergroup called the Rhizaria

Rhizaria

The Rhizaria are a species-rich supergroup of protists. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods....
.

The best-known Cercozoa are the euglyphid

Euglyphid

The euglyphids are a prominent group of filose amoeboide that produce shells or tests from siliceous scales, plates, and sometimes spines. These elements are created within the cell and then assembled on its surface in a more or less regular arrangement, giving the test a textured appearance....
s, filose amoebae with shells of siliceous scales or plates, which are commonly found in soils, nutrient-rich waters, and on aquatic plants.

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Encyclopedia

The Cercozoa are a group of protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s, including most amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
s and flagellate

Flagellate

Cytostome

Foraminifera

Rhizaria

Euglyphid

Tectofilosid

The tectofilosids or amphitremids are a group of filose amoeboide with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales....
s and Gromia
Gromia

Gromia is a widespread genus of marine and freshwater amoeboids, closely resembling some foraminiferans. It produces an organic test, which is ovoid or lobed and may exceed one millimetre in size; this resembles a small grape, in that its centre is fluid-filled but lacks organic matter, which is concentrated in its translucent test and u...
. 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 chlorarachniophyte

Chlorarachniophyte

Chlorarachniophytes are a small group of algae occasionally found in tropical oceans. They are typically mixotrophic, ingesting bacterium and smaller protists as well as conducting photosynthesis....
s, strange amoebae that form a reticulating net. They are set apart by the presence of chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryote organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve Thermodynamic free energy in the form of Adenosine triphosphate and reduce NADP to NADPH through a complex set of processes called photosynthesis....
s, 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 cercomonad

Cercomonad

Cercomonads are small flagellates, widespread in aqueous habitats and especially common in soils. The cells are generally around 10 μm in length, without any shell or covering....
s, which are common soil flagellates, and the Phaeodarea

Phaeodarea

The Phaeodarea are a group of amoeboid protists. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa....
, marine protozoa that were previously considered radiolarians. In addition, three groups that are traditionally considered heliozoa

Heliozoa

Heliozoa, or sun animalcules, are roughly spherical amoeboids with many stiff, microtubule-supported projections called axopods radiating outward from the cell surface....
ns belong here: the dimorphid

Dimorphid

The dimorphids or heliomonads are a small group of heliozoa that are unusual in possessing flagellum throughout their life-cycle. There are two genera: Dimorpha, a tiny organism found in freshwater, and the larger Tetradimorpha, which is distinguished by having four rather than two flagella....
s, desmothoracid

Desmothoracid

The desmothoracids are a group of heliozoan protists, usually sessile and found in freshwater environments. Each adult is a spherical cell around 10-20 ?m in diameter surrounded by a perforated organic lorica or shell, with many radial pseudopods projecting through the holes to capture food....
s, and gymnosphaerid

Gymnosphaerid

The gymnosphaerids are a small group of heliozoan protists found in marine environments. They tend to be roughly spherical with radially directed axopods, supported by microtubules in a triangular-hexagonal array arising from an amorphous central granule....
s. The exact composition and classification of the Cercozoa are still being worked out. A general scheme is:

Class Chlorarachnea		chlorarachniophyte Chlorarachniophyte Chlorarachniophytes are a small group of algae occasionally found in tropical oceans. They are typically mixotrophic, ingesting bacterium and smaller protists as well as conducting photosynthesis.... s
Class Proteomyxidea		gymnophryid Gymnophryid The gymnophryids are a small group of amoeboids that lack shells and produce thin, reticulose pseudopods. These contain microtubules and have a granular appearance, owing to the presence of extrusomes, but are distinct from the pseudopods of Foraminifera.... s, dimorphid Dimorphid The dimorphids or heliomonads are a small group of heliozoa that are unusual in possessing flagellum throughout their life-cycle. There are two genera: Dimorpha, a tiny organism found in freshwater, and the larger Tetradimorpha, which is distinguished by having four rather than two flagella.... s, desmothoracid Desmothoracid The desmothoracids are a group of heliozoan protists, usually sessile and found in freshwater environments. Each adult is a spherical cell around 10-20 ?m in diameter surrounded by a perforated organic lorica or shell, with many radial pseudopods projecting through the holes to capture food.... s, gymnosphaerid Gymnosphaerid The gymnosphaerids are a small group of heliozoan protists found in marine environments. They tend to be roughly spherical with radially directed axopods, supported by microtubules in a triangular-hexagonal array arising from an amorphous central granule.... s, etc.
Class Sarcomonadea		cercomonad Cercomonad Cercomonads are small flagellates, widespread in aqueous habitats and especially common in soils. The cells are generally around 10 μm in length, without any shell or covering.... s
Class Imbricatea / Silicofilosea		euglyphid Euglyphid The euglyphids are a prominent group of filose amoeboide that produce shells or tests from siliceous scales, plates, and sometimes spines. These elements are created within the cell and then assembled on its surface in a more or less regular arrangement, giving the test a textured appearance.... s and thaumatomonads
Class Thecofilosea		tectofilosid Tectofilosid The tectofilosids or amphitremids are a group of filose amoeboide with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales.... s and cryomonads
Class Phaeodarea Phaeodarea The Phaeodarea are a group of amoeboid protists. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa....
Class Ebridea		ebriid Ebriid The Ebridea is a group of phagotrophic flagellate protist present in marine coastal plankton communities worldwide. Ebria tripartita is one of two described extant species in the Ebridea.... s

In addition two groups of parasites, the Phytomyxea

Phytomyxea

The Phytomyxea are a group of protists that are parasites of plants. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa....
and Ascetosporea

Ascetosporea

The Ascetosporea are a group of protists that are parasites of animals, especially marine invertebrates. There are two groups, the haplosporids and paramyxids, which are not particularly similar morphologically but consistently group together on molecular trees, which place them near the base of the Cercozoa....
, and the shelled amoeba Gromia
Gromia

Gromia is a widespread genus of marine and freshwater amoeboids, closely resembling some foraminiferans. It produces an organic test, which is ovoid or lobed and may exceed one millimetre in size; this resembles a small grape, in that its centre is fluid-filled but lacks organic matter, which is concentrated in its translucent test and u...
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

Amoebozoa

The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
. 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.