They can be classified into three general groups based on their shape. You can just see the thin cilia poking out around the edges of the protozoan in the image to the right. To hunt, protozoa have to be able to move about. Amoebae have fluid cell membranes or coverings that they can stretch out, bend and curve. As the membrane moves outward, the fluid and other parts inside the cell follow, flowing into the new bulge created by the moving membrane.
Many ciliates swim along by beating their cilia in a rhythmic pattern, like so many tiny oars.
Flagellates swim by waving their flagella, using them much like a fish uses its tail push itself through water. Some protozoa prefer to latch themselves in one place. It creates a mini whirlpool around its mouth pore by beating the cilia ringing its bulbous top end so that food particles get sucked in. Whenever anything too big to be eaten hits a Vorticella , it springs back out of the way by by rapidly coiling up its stalk. The vast majority of protozoa do us no harm.