Amoeboid

Amoeboid describes a mode of locomotion and cell shape change based on the extension of cytoplasmic projections called pseudopodia. The term applies to the movement style of many protists, as well as certain animal and fungal cells, rather than to a single taxonomic group.

Most amoeboid cells propel themselves by assembling actin filaments at the leading edge to push out a pseudopodium, anchor the front with adhesion molecules, and then pull the cell body forward as the rear flows forward. The process yields a characteristic irregular outline and frequent changes in shape. Pseudopodia types include lobopodia (bulky extensions) and thin filopodia; some forms also use blebs.

Organisms exhibiting amoeboid movement include free-living amoebae such as Amoeba proteus, parasitic species like Entamoeba histolytica, and the cellular slime mold Dictyostelium discoideum. In animals, amoeboid motility is essential for leukocytes, enabling chemotaxis toward infection sites. Diet is typically phagocytosis of bacteria, yeasts, and debris; some species encyst or form cysts for survival.

Size varies; many amoebae range from about 10 to 600 micrometers in diameter, though shapes are highly plastic. Amoeboid movement relies on the cytoskeleton, membrane dynamics, and sometimes changes in cytoplasmic viscosity, or sol–gel transitions.

Because amoeboid movement is widespread across life, the term remains descriptive rather than taxonomic, emphasizing function and mechanism rather than a single lineage.