Kingdom: Protozoa (Unicellular Organisms)

Protozoa is diverse group of over 65,000 species of single-celled eukaryotes (organisms whose cells have nuclei) that commonly show characteristics usually associated with animals, most notably mobility and heterotrophy, but they possess a simpler and more primitive structure than the members of the animal kingdom. A heterotroph is an organism that cannot produce its own food and has to obtain its nutrition from other sources of organic carbon such as plant or animal matter. They live in a wide variety of moist habitats including fresh water, marine environments and the soil. Some species are parasitic, meaning they live in other plants and animals, including humans, where they cause disease. Protozoa have many different shapes and sizes; some such as an Amoeba can change their shape while others have a fixed shape and more complex structure.