Definition of Protozoan

Protozoa (in Greek proto = first and zoa = animals) are one-celled eukaryotes (that is, unicellular microbes whose cells have membrane-bound nuclei) that commonly show characteristics usually associated with animals,  mobility and heterotrophy. Protozoans were commonly grouped in the kingdom Protista together with the plant-like algae and fungus-like water molds and slime molds. In 21st-century systematics, however, most of the algae are classified in kingdoms such as Plantae and Chromista; and in such cases the remaining life forms are occasionally classified as a kingdom Protozoa. But the name is misleading, since protozoans are neither Animalia nor Metazoa, with the possible exception of the enigmatic, moldy Myxozoa).