The Amoebae . The World of Parasites. William R. Pendergras. Most protozoans are microscopic, but certain amoebae reach up to 4 to 5 mm in diameter, and the shells of their cousins the foraminifera may be 10 cm across. Protozoa are classified into three groups based on their shape.
Ciliates are the largest and move by means of hair like cilia.
They eat the other two types of protozoa, as well as bacteria. Amoebae also can be quite large and move by temporary foot. Amoebae are further divided into testate amoebae that make a shell like covering and naked amoebae without a covering. Flagellates are the smallest of the protozoa and use a few whip like flagella to move. In amoeba, actin and myosin are organized into a three dimensional network.