Protozoa (subkingdom)

Subkingdom of single-celled, non-photosynthetic organisms containing all the minute organelles and chemicals needed to live, with locomotary structures such as cilia or flagella, and sometimes an exoskeleton; they exist singly or gathered into colonies. They were formerly classified in the animal kingdom. Although they comprise a subkingdom, protozoans are not necessarily related to one another, as they are not a natural group, but simply a collection of organisms. There are more than 65,000 described species, of which over half are fossil.