Pseudopod in the context of "Chaos carolinense"

Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, named Amorphea.Amoebozoa includes many of the best-known amoeboid organisms, such as Chaos, Entamoeba, Pelomyxa and the genus Amoeba itself. Species of Amoebozoa may be either shelled (testate) or naked, and cells may possess flagella. Free-living species are common in both salt and freshwater as well as soil, moss and leaf litter. Some live as parasites or symbionts of other organisms, and some are known to cause disease in humans and other organisms.

While the majority of amoebozoan species are unicellular, the group also includes several clades of slime molds, which have a macroscopic, multicellular stage of life during which individual amoeboid cells remain together after multiple cell division to form a macroscopic plasmodium or, in cellular slime molds, aggregate to form one.

The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, 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 (thecae or loricas), which are in different clades within Rhizaria made out of opal (SiO₂), celestite (SrSO₄), or calcite (CaCO₃).

The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplast—with an apical complex membrane. The organelle's apical shape is an adaptation that the apicomplexan applies in penetrating a host cell.

The Apicomplexa are unicellular and spore-forming. Most are obligate endoparasites of animals, except Nephromyces, a symbiont in marine animals, originally classified as a chytrid fungus, and the Chromerida, some of which are photosynthetic partners of corals. Motile structures such as flagella or pseudopods are present only in certain gamete stages.

Amoeboid movement is the most typical mode of locomotion in adherent eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia ("false-feet") and posterior uropods. One or more pseudopodia may be produced at a time depending on the organism, but all amoeboid movement is characterized by the movement of organisms with an amorphous form that possess no set motility structures.

Movement occurs when the cytoplasm slides and forms a pseudopodium in front to pull the cell forward. Some examples of organisms that exhibit this type of locomotion are amoebae (such as Amoeba proteus and Naegleria gruberi,) and slime molds, as well as some cells in humans such as leukocytes. Sarcomas, or cancers arising from connective tissue cells, are particularly adept at amoeboid movement, thus leading to their high rate of metastasis.

The nucleariids, or nucleariid amoebae, are a group of amoebae that comprise the sister clade of the fungi. Together, they form the clade Holomycota. They are aquatic organisms found in freshwater and marine habitats, as well as in faeces. They are free-living phagotrophic predators that mostly consume algae and bacteria.

Nucleariids are characterized by simple, spherical or flattened single-celled bodies with filopodia (fine, thread-like pseudopods), covered by a mucous coat. They lack flagella and microtubules. Inside the cytoplasm of some species are endosymbiotic proteobacteria. Some species are naked, with only the mucous coat as cover, while others (known as 'scaled' nucleariids) have silica-based or exogenous particles of various shapes.

Actin filaments (also known as microfilaments) are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other proteins in the cell. Actin filaments are usually about 7 nm in diameter and made up of two strands of actin. Microfilament functions include cytokinesis, amoeboid movement, cell motility, changes in cell shape, endocytosis and exocytosis, cell contractility, and mechanical stability. In inducing cell motility, one end of the actin filament elongates while the other end contracts, presumably by myosin II molecular motors. Additionally, they function as part of actomyosin-driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's ATP-dependent pulling action in muscle contraction and pseudopod advancement. Microfilaments have a tough, flexible framework which helps the cell in movement.

Actin was first discovered in rabbit skeletal muscle in the mid 1940s by F.B. Straub. Almost 20 years later, H.E. Huxley demonstrated that actin is essential for muscle contraction. The mechanism in which actin creates long filaments was first described in the mid 1980s. Later studies showed that actin has an important role in cell shape, motility, and cytokinesis.