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a temporary protrusion of cytoplasm in unicellular organisms (rhizopods, some flagellates, sporozoans, and myxomycetes) and in some multicellular organisms (leukocytes; macrophages; the eggs of sponges, coelenterates, and acoelomate tubellarians; some cells in tissue cultures).
Pseudopodia aid in amoeboid locomotion and enable the organisms to grasp food or foreign particles. Since the pseudopodia can appear and be withdrawn again in different parts of the cell, the shape of the cells in amoeboid locomotion is constantly changing. The formation of pseudopodia and amoeboid locomotion result from local changes in the surface tension of the cell and from little-studied mechanisms of overflow, contraction, extension, and liquefaction of the cytoplasm.
In amoebas, the pseudopodia are lobed or filiform. In foraminiferans and radiolarians, they are branched, thin, and long, and they coalesce with one another. The pseudopodia of sun animalcules contain a solid, elastic axial filament (axopodium), which is responsible for the flexibility and constancy of the shape of the organisms. The pseudopodia are usually digitiform or lobed in the amoeboid cells of multicellular organisms.