pseudopodium, temporary or semipermanent extension of the cytoplasm, used in locomotion and feeding by all sarcodine protozoans (i.e., those with pseudopodia; see sarcodine) and some flagellate protozoans. Pseudopodia are formed by some cells of higher animals (e.g., white blood corpuscles) and by amoebas. During amoeboid feeding, pseudopodia either flow around and engulf prey or trap it in a fine, sticky mesh.
Protozoans have four types of pseudopodia. Lobopodia, characteristic of Amoeba, are blunt and fingerlike; filopodia are slender and tapering, occasionally forming simple, branched networks; reticulopodia, found in the foraminiferans, are branching filaments that fuse to form food traps; and axopodia, characteristic of the actinopods, are long and sticky (like reticulopodia) but radiate singly and have a stiff, internal rod composed of numerous microtubules. Lobopodia and filopodia are formed as the result of a pressure system; reticulopodia and axopodia depend on a two-way flow of cytoplasm.