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A protist (/ ˈ p r oʊ t ɪ s t / PROH-tist) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus.Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
All eukaryotes apart from animals, plants and fungi are considered protists. [1] Its field of study therefore overlaps with the more traditional disciplines of phycology , mycology , and protozoology , just as protists embrace mostly unicellular organisms described as algae , some organisms regarded previously as primitive fungi , and protozoa ...
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes (bacteria and archaea) and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms ...
A protist (/ ˈ p r oʊ t ɪ s t /) is any eukaryotic organism (one with cells containing a nucleus) that is not an animal, plant, or fungus.The protists do not form a natural group, or clade, since they exclude certain eukaryotes with whom they share a common ancestor; [a] but, like algae or invertebrates, the grouping is used for convenience.
One of the shared features of these organisms is their motility, crucial for nutrient acquisition and avoidance of danger. [7] In the process of evolution, single-celled organisms have developed in a variety of directions, and thus their rich morphology results in a large spectrum of swimming modes. [8] [2]
By 1981, Cavalier-Smith had divided all the eukaryotes into nine kingdoms. [20] In it, he created Chromista for a separate kingdom of some protists. [21] Most chromists are photosynthetic. This distinguishes them from most other protists which lack photosynthesis. In both plants and chromists photosynthesis takes place in chloroplasts.
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) that feed by heterotrophy. [9]
Still, he is controversial in a way that is a bit difficult to describe. The issue may be one of writing style. Cavalier-Smith has a tendency to make pronouncements where others would use declarative sentences, to use declarative sentences where others would express an opinion, and to express opinions where angels would fear to tread.