Figure 4. All known organisms are classified within successively larger categories according to the traits they have in common. Thus, the Kingdom Protista encompasses single-celled animals, the Phylum Sarcodina applies to those single-celled protists that possess cytoplasmic extensions or pseudopodia used for locomotion and prey capture, and so on. The figure illustrates the position of the Polycystina within this system, as well as its subdivisions into lower categories.