Phylum Amoebozoa Lühe, 1913, emend. Cavalier-Smith, 1998

Organisms almost universally exhibit amoeboid activity during their life cycle. Amoeboid locomotion occurs either through lobopodia with directed cytoplasmic streaming or through eruptive movements, depending on the lineage. Alternatively, locomotion may involve the extension and retraction of pseudopodia or subpseudopodia with limited cytoplasmic flow. Cells are typically naked, often surrounded by a well-developed glycocalyx; in some groups they are covered by a tectum or cuticle or extracellular envelope. Testate forms (e.g., Arcellinida) possess a flexible or rigid shell with one or several apertures. Mitochondrial cristae are generally tubular (ramicristate), with reduction to mitochondrion-related organelles (MROs) in Archamoebae. Most taxa are reported as asexual, yet sexual cycles or processes consistent with sex have been documented in all three major lineages—Tubulinea, Evosea, and Discosea. Fruiting structures are common, either sporocarpic or sorocarpic. Biciliate, uniciliate, or multiciliate stages occur in some taxa; in certain lineages the ancestral bikont kinetid has been reduced to a unikont kinetid.

Most amoebozoans are unicellular, uninucleate, binucleate, or multinucleate, with sizes ranging from approximately 2 μm to several millimeters. Slime molds consist of amoeboid cells that aggregate into plasmodia or multicellular structures, which in some species may extend over several square meters.

Free-living species are widespread in marine, brackish, and freshwater environments, as well as in soil, mosses, and leaf litter. Some amoebozoans are parasitic or symbiotic, and several are pathogenic to humans and other organisms.

Phylogenetically, Amoebozoa form the sister group to Opisthokonta (animals and fungi), a relationship consistently recovered in multigene and phylogenomic analyses.

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