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Synopsis Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in moder taxonomy. The protists do not have much in common besides a relatively simple organization-either they are unicellular, or they are multicellular without specialized tissues. This simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants.

The term 'protista' was first used by Ernst Haeckel in 1866. Protists were traditionally subdivided into several groups based on similarities to the higher kingdoms : the one-velled animal-like protozoa, the plant-like protophyta (mostly one-celled algae), and the fungus-like slime molds and water molds. Because these groups often overlap, they have been replaced by phylogenetic-based classifications. However, they are still useful as informal names for describing the morphology and ecology of protists.