Protozoan

Protozoan, single-celled organism belonging to the phylum Protozoa. Protozoans fall into 4 classes: flagellates, sarcodines, sporozoans, and ciliates. Most are aquatic, living in fresh or salt water. Some live in plants or animals and cause serious diseases. A few protozoans contain chlorophyll and make their own food, but the majority must ingest their food. They reproduce in many ways, including undergoing fission (cell division) or budding. Protozoans tend to be solitary; a few cluster in colonies.