The subphylum Sarcodina contains those protozoa in which adults possess flowing extensions of the body called pseudopodia. Pseudopodia are used for capturing prey in all Sarcodina, and in benthic groups, pseudopodia are also used as locom otor organelles.

The subphylum includes the familiar amebas as well as many other marine, freshwater, and terrestrial forms. The slime molds are sometimes included in the Sarcodina, but in the following discussion, the slim e m olds will be considered to be fungi and left to the mycologists.

The Sarcodina either are asymmetrical or have a spherical symmetry. They possess relatively few organelles and in this respect are perhaps the simplest protozoa. However, skeletal structures, which are found in the majority of species, reach a complexity and beauty that is surpassed by few other organisms.

The presence of flagellated gametes among many Sarcodina and the tendency of many flagellates to lose their flagella during some phase of the life cycle, often becoming ameboid, are important reasons for uniting the mastigophorans and sarcodines within a single phylum. These facts would also seem to indicate that the Mastigophora are the ancestral group.