Phylum Amoebozoa Lühe, 1913, emend. Cavalier-Smith, 1998
Organisms almost all demonstrating ‘amoeboid activity’ in all or in certain stage(s) of their life cycle. Amoeboid locomotion with steady flow of the cytoplasm or occasional eruptions in some groups; alternatively, amoeboid locomotion involving the extension and retraction of pseudopodia and/or subpseudopodia with little coordinated movement of the cytoplasm. Cells naked, often with well-developed, differentiated glycocalyx; in several groups cells are covered with a tectum or a cuticle. Two groups are testate (enclosed in a flexible or hard extracellular envelope with one to several opening(s)). Mitochondrial cristae tubular (ramicristate), with few exceptions; mitochondria secondarily reduced to mitochondrion-related organelles (MRO) in archamoebians. Most only reported to be asexual, but sex and life cycles consistent with sex have been reported in all three major lineages—Tubulinea, Evosea and Discosea. Many taxa exhibit either sporocarpic or sorocarpic fruiting. Biciliated, uniciliated or multiciliated stages in the life cycle of some taxa; some taxa exhibit reduction of the bikont kinetid to a unikont kinetid.
The majority of amoebozoan protists are unicellular, uninucleate, binucleate or multinucleate, and vary in size from about 2 μm to several millimeters in diameter. Slime molds are amoeboid cells which aggregate into multicellular organism which in some species can cover an area of several square meters.
Free-living species are widespread and common in salt, brackish and freshwater, as well as in soil, moss and leaf litter. Some amoebozoa are parasites or live as symbiotes of other organisms. Some are known to cause disease in humans and other organisms.
Amoebozoa form a sister group to animals and fungi.