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Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.
The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons, which are in different clades within Rhizaria made out of opal, celestite, or calcite. Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.
Cercomonads are small amoeboflagellates, widespread in aqueous habitats and common in soils.
The tectofilosids are a group of filose amoebae with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales. The shell usually has a single opening, but in Amphitrema and a few other genera it has two on opposite ends. The cell itself occupies most of the shell. They are most often found on marsh plants such as Sphagnum.
Reticulosida is an order of Cercozoa that was created by Cavalier-Smith in 2003, but subsequently emended in by Bass et al. in 2009 to include only one monotypic family, the Filoretidae.
Monadofilosa is a grouping of Cercozoa. These organisms are single-celled amoeboid protists.
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa.
Endomyxa is a group of eukaryotic organisms in the supergroup Rhizaria. They were initially a subphylum of Cercozoa and later a subphylum of Retaria, but several analyses have proven they are a phylogenetically separate lineage, and Endomyxa is currently regarded as its own phylum.
Thaumatomonadida is an order of flagellates.
Imbricatea is a class of Rhizaria characterised by silica scales. It is sometimes described as "Imbricatea/Silicofilosea", due to the similarity of those two groupings. Imbricatea is divided into the orders Euglyphida and Thaumatomonadida.
Cryomonadida is a group of heterotrophic Rhizaria, that belong to the Cercozoa.
Thecofilosea is a class of unicellular testate amoebae belonging to the phylum Cercozoa. They are amoeboflagellates, organisms with flagella and pseudopodia, distinguished from other cercozoa by their scale-lacking test composed of organic material. They are closely related to the Imbricatea, a group of testate amoebae with tests composed of inorganic silica scales.
The spongomonads are a group of flagellated protists in the phylum Cercozoa. Taxonomically, they compose the family Sarcomonadidae and order Sarcomonadida. They were originally placed among the Reticulofilosa, but were later transferred to Monadofilosa. It includes only two genera:
Heliomorpha is a genus of Cercozoa, placed in its own family, Heliomorphidae. It used to be known as "Dimorpha", but that name was a junior synonym several times over.
The sarcomonads or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or external theca, a soft cell surface without obvious cortical filamentous or membranous skeleton, two cilia without scales or hairs, tubular mitochondrial cristae, near-spherical extrusomes, and a microbody attached to the nucleus.
Paracercomonas is a genus of rhizaria.
Ebria is a genus of rhizaria.
Katabia is a genus of soil-dwelling heterotrophic flagellate cercozoans containing the single species Katabia gromovi, and the only member of family Katabiidae.
The paracercomonads are a group of cercozoan protists. Taxonomically, they comprise the family Paracercomonadidae, order Paracercomonadida and subclass Paracercomonada. Due to their morphological similarities to the cercomonads, members of this family were grouped with Cercomonas and similar taxa from the beginning. However, their similarities are due to convergent evolution.
Ventrifilosa is a highly diverse group of phagotrophic protists that glide through their flagella and emit filose pseudopods from their ventral side for feeding. Because of their mixture of amoeba and flagellate characteristics, they are amoeboflagellates. Members of this group are the Imbricatea, Sarcomonadea and Thecofilosea.
References
- ↑ Karpov, S.; Bass, D.; Mylnikov, A.; Cavalier-Smith, T. (2006). "Molecular phylogeny of Cercomonadidae and kinetid patterns of Cercomonas and Eocercomonas gen. Nov. (Cercomonadida, Cercozoa)". Protist. 157 (2): 125–158. doi:10.1016/j.protis.2006.01.001. PMID 16647880.
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