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The Amoebozoa are a major group of amoeboid protozoa, comprising the majority of the amoebae that move using blunt or lobose pseudopods. Most members are unicellular, for instance the famous species Amoeba proteus, which is often studied in laboratories. They include the most common protists in soils and aquatic habitats. Some are symbiotic on other organisms, including some pathogens, responsible for dysentery and other diseases. They also include most slime moulds (Mycetozoa), multinucleate or multicellular forms that produce spores, and are often visible to the unaided eye.
Amoebozoans rely on pseudopods for both locomotion and feeding. The majority lack flagella, and more generally do not form microtubule-supported structures except during mitosis. The cell is typically divided into an outer layer of clear ectoplasm and an inner layer of granular endoplasm. In the active form there is usually one or more pseudopods along the anterior margin and sometimes a posterior bulb called a uroid, which may support slender projections. A number of amoebae produce shells from secreted materials, as in Arcella, or by cementing together collected materials, as in Difflugia.
Locomotion usually takes place by the cell mass flowing into one of the leading pseudopods, as in Amoeba, but there is notable variation. For instance, some amoebae crawl using relatively permanent pseudopods as limbs. Unlike the superficially similar but unrelated heteroloboseans, which pass through both amoeboid and flagellate stages, pseudopod formation is typically smooth and non-eruptive. The primary mode of nutrition is phagocytosis: the cell surrounds potential food particles, sealing them into vacuoles where they may be digested and absorbed. When food is scarce, most amoebae can form cysts, which may be carried aerially and introduce them to new environments. The spores of slime molds serve a similar purpose.
Most amoebozoans have mitochondria, which characteristically have tubular, branching cristae. However, a few have secondarily lost them, collectively referred to as archamoebae from an earlier assumption that the condition was primitive. These comprise the giant amoeba PelomyxaPelomyxa are giant amoebae, usually 500-800 μm, but occasionally passing 3 mm in length. The most notable species is P. palustris other described species may be synonyms. They are found in mud at the bottom of freshwater streams. A moving cell is cylin, the parasitic entamoebaThe entamoebae are a group of parasitic and commensal amoebae which lack mitochondria. They include several species that are pathenogenic in humans, most notably Entamoeba histolytica which causes amoebic dysentery. Cells are uninucleate and small, typicae, and the uniflagellate mastigamoebaeThe pelobionts are a small group of amoebae that lack mitochondria. The most notable member is Pelomyxa called giant amoebae because they reach sizes of up to 3 mm. They also include the flagellated amoebae Mastigamoeba Mastigella and Mastigina''. Both pe. Flagellate cells are also found among certain slime moulds. They generally have a cone of microtubules anchoring the flagellum, suggesting a close relationship to the opisthokontThe opisthokonts are a broad group of eukaryotes, including both the animals and fungi, together with a few sorts of protists. That these form a monophyletic group is strongly supported by both genetic and ultrastructural studies. One common characteristis.
Although many amoebae are only around 10-20 μmTo help compare different orders of magnitude this page lists lengths between 10 micrometre and 100 micrometre (10-5 m and 10-4 m). See also lengths of other orders of magnitude. Shorter lengths 10 µm, width of cotton fibre 10. 6 µm, wavelength of light e in diameter, they also include many of the larger protozoa. For instance A. proteus may reach 800 μmTo help compare different orders of magnitude this page lists lengths between 100 µm and 1 mm (10-4 m and 10-3 m). See also lengths of other orders of magnitude. Shorter distances 100 micrometre is equal to 1/10th of a millimetre, 0. 00394 inches. 125 µm, in length, and Pelomyxa are often several millimetres long. Most slime moulds take the form of giant multinucleateIn cell biology, the nucleus is an organelle, found in most eukaryotic cells, which contains most of the cell's genetic material. Nuclei have two primary functions: to control chemical reactions within the cytoplasm and to store information needed for cel amoebae called plasmodia , and the largest may cover several square feet. In contrast, cellular slime moulds survive as separate amoebae most of the time but under appropriate conditions aggregate to form fruiting bodies.
