Abstract is: A protist (/ˈproʊtɪst/) is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exclusion of other eukaryotes means that protists do not form a natural group, or clade. Therefore, some protists may be more closely related to animals, plants, or fungi than they are to other protists. However, like the groups algae, invertebrates, and protozoans, the biological category protist is used for convenience. Others classify any unicellular eukaryotic microorganism as a protist. The study of protists is termed protistology.