Pseudopodial Locomotion

Pseudopodial Locomotion

Some protozoans, most notably amoeboid forms, move not by beating a flagellum or cilia but by extending temporary projections of their own cell body called pseudopodia ("false feet"). A pseudopodium is formed by the local, directed flow of cytoplasm toward one part of the cell surface, causing the cell membrane at that point to bulge outward; the rest of the cell body then flows into this extension, and the process is repeated in the desired direction of movement, allowing the whole cell to "creep" across a surface. Pseudopodia also serve a feeding role, since many amoeboid protozoans engulf food particles by extending pseudopodia around them (phagocytosis).

Pseudopodia themselves take different forms depending on the protozoan group, and two contrasting types are commonly distinguished:

• Lobopodium — a broad, blunt, finger- or lobe-shaped pseudopodium, typically containing both the clearer outer cytoplasm (ectoplasm) and the granular inner cytoplasm (endoplasm) flowing into it; this is the classic pseudopodium type seen in Amoeba.
• Filopodium — a slender, thread-like, pointed pseudopodium, generally narrower and more rigid than a lobopodium, often containing only the clearer ectoplasm rather than the full flow of granular endoplasm, and sometimes branching; filopodia are seen in certain amoeboid protozoan groups distinct from Amoeba itself. …