members being derived from one common ancestor that is itself regarded as belonging in the taxon), and holophyletic (containing all of the known descendants of that common ancestor). The taxon 'Protozoa' fails to meet these standards, so grouping protozoa with animals, and treating them as closely related, became no longer justifiable.

The term continues to be used in a loose way to describe single-celled protists (that is, eukaryotes that are not animals, plants, or fungi)