According to the University of Colorado, organisms in the phylum Protazoa are the animal-like members of Kingdom Protista. These organisms are mostly single-celled, although there are several multicellular protist species. All protists obtain nutrients by feeding on other living things, and they are mobile. Their cells are eukaryotic and contain developed organelles, but they lack cell walls.
According to Education Portal, protazoans are more complex than bacteria. Each protazoan cell contains many complex organelles, all of which carry out specific functions to contribute to the organism's overall well-being. Some protist species even have parts that are analogous to mouths and digestive tracts.
Many, but not all protazoans, cause disease in humans. Education Portal states that Plasmodium, which causes malaria, is a protazoan, as is Trichomonas, an organism that causes a sexually transmitted disease.
Protazoans are a very diverse group of organisms, so scientists split them into four main categories. The Flagellates, according to Education Portal, are those which move around by use of a whip-like tail called a flagellum. Amoebas are protazoans that have cell membranes that do not include structural components; as a result, they take on a blob-like shape. Ciliates are covered in tiny cilia which aid in motility, and the final group, Sporozoans, have a mature form that is completely non-motile.