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Any member of a kingdom (Protista) of diverse eukaryotes, including algae, protozoans, and lower fungi (seefungus). Most are single-celled organisms, though the algae tend to be multicellular. Many can move, mainly by using flagella (seeflagellum), cilia (seecilium), or footlike extensions (pseudopodia). The kingdom was developed to accommodate intermediate organisms that, even though they possessed some plant or animal characteristics, did not exhibit the specialized features indicative of those groups. Some protists are considered the ancestors of multicellular plants, animals, and fungi. The term was first suggested in 1866 by Ernst Haeckel. With the development of advanced biochemical, genetic, and imaging techniques, previously established relationships have come under scrutiny, and it is now thought that some groups are less closely related to one another than once believed. As a result, the classification of protists, while convenient, is no longer entirely satisfactory.
This entry comes from Encyclopædia Britannica Concise. For the full entry on protist, visit Britannica.com.