Cercozoa

Cercozoa (now synonymised with Filosa) is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined 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 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 and have proven difficult to define in terms of structural characteristics, although their unity is strongly supported by phylogenetic studies. Some cercozoans are grouped by whether they are "filose" or "reticulose" in the behavior of their cytoskeleton when moving: Filose, meaning their pseudopods develop as filopodia. For example: Euglyphids, filose amoebae with shells of siliceous scales or plates, which are commonly found in soils, nutrient-rich waters, and on aquatic plants. Gromia, a shelled amoeba. Tectofilosids, filose amoebae that produce organic shells. Cercomonads, common soil-dwelling amoeboflagellates. Reticulose, meaning they form a reticulating net of pseudopods. For example: Chlorarachniophytes, set apart by the presence of chloroplasts 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 important ecological groups are: Granofilosea, comprising several groups traditionally considered heliozoa such as Heliomonadida, Desmothoracida and Gymnosphaerida. Phaeodaria, marine protozoa previously considered radiolarians.