Protists are the oldest eukaryotic microorganisms, having a nucleus and other membrane-bound organelles. Since they do not wholly fit into other groups like plants, animals, bacteria, or fungi, they are categorized under a separate kingdom called Protista.
Protists are defined as all eukaryotes that are not animals, land plants or fungi, the three traditional "higher" kingdoms of eukaryotes.
Many different naming schemes were used over the last couple of centuries, but it has become the most common practice to refer to eukaryotes that are not land plants, animals, or fungi as protists.
Eukaryotic organisms that did not fit the criteria for the kingdoms Animalia, Fungi, or Plantae historically were called protists and were classified into the kingdom Protista.
Various definitions of protists exist, including a phylogenetic perspective that classifies them as all eukaryotes except for animals, fungi, or land plants (Embryophyta).
Most protists are microscopic, unicellular organisms that are abundant in soil, freshwater, brackish, and marine environments. They are also common in the digestive tracts of animals and in the vascular tissues of plants.
Nature: Symbionts of predatory protists are widespread in the oceans and related to animal pathogens
Symbionts of predatory protists are widespread in the oceans and related to animal pathogens
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