Protozoa
Protozoa or protista are single-celled creatures with nuclei which show some characteristics, such as heterotrophy and motility, usually associated with animals. They are now generally included in the eukaryote kingdom Protista, together with the plant-like algae. Occasionally some groups of protozoa may also be treated as independent kingdoms.
Most protozoans are too small to be seen with the naked eye - most are around 0.01-0.05 mm, although forms up to 0.5 mm are still fairly common - but can easily be found under a microscope. Protozoa are ubiquitous throughout aqueous environments and the soil, and play an important role in their ecology. A few are also important parasites.
