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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.
A variety of multi-kingdom systems were proposed, and the Kingdoms Protista and Protoctista became established in biology texts and curricula. [ 22 ] [ 23 ] [ 24 ] By 1954, Protozoa were classified as "unicellular animals", as distinct from the "Protophyta", single-celled photosynthetic algae, which were considered primitive plants. [ 25 ]
Protistology is a scientific discipline devoted to the study of protists, a highly diverse group of eukaryotic organisms. All eukaryotes apart from animals, plants and fungi are considered protists. [1]
Protists have been described as a taxonomic grab bag of misfits where anything that doesn't fit into one of the main biological kingdoms can be placed. [98] Some modern authors prefer to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellular organisms.
Some modern authors prefer to exclude multicellular organisms from the traditional definition of a protist, restricting protists to unicellular organisms. [9] [10] This more constrained definition excludes all brown, the multicellular red and green algae, and, sometimes, slime molds (slime molds excluded when multicellularity is defined as ...
Ciliates are an important group of protists, common almost anywhere there is water—in lakes, ponds, oceans, rivers, and soils, including anoxic and oxygen-depleted habitats. [2] About 4,500 unique free-living species have been described, and the potential number of extant species is estimated at 27,000–40,000. [ 3 ]
Protists reproduce asexually or sexually. If the protists reproduce asexually, they do so through binary fission, multiple fission, budding, and fragmentation. If the protists reproduce sexually, they do so through a syngamy process where there is a fusion of the gametes. If this occurs in an individual it is recognized as autogamy.
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, [8] often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. [7] [9] In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista [10] or the kingdom Protozoa.