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The usage of higher-level taxon ranks (phylum and kingdom) is unstable, as it varies from one author to the next; [8] [9] as such, said ranks are generally omitted. The following cladogram shows the relationships between the major groups of protists, as well as the kingdoms of animals, plants and fungi, according to the most recent phylogenetic ...
The differences between fungi and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification, [8] but was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the Fungi. [11]
Microscopic organisms were increasingly constrained in the plant/animal dichotomy. In 1858, the palaeontolgist Richard Owen was the first to define Protozoa as a separate kingdom of eukaryotic organisms, with "nucleated cells" and the "common organic characters" of plants and animals, although he also included sponges within protozoa. [28]
In 1866, Ernst Haeckel proposed a third kingdom of life, which he named Protista. At first, Haeckel included a few multicellular organisms in this kingdom, but in later work, he restricted the Protista to single-celled organisms, or simple colonies whose individual cells are not differentiated into different kinds of tissues. [21]
Amoebozoa includes many of the best-known amoeboid organisms, such as Chaos, Entamoeba, Pelomyxa and the genus Amoeba itself. Species of Amoebozoa may be either shelled (testate) or naked, and cells may possess flagella. Free-living species are common in both salt and freshwater as well as soil, moss and leaf litter.
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 ...
Animals and fungi are also more closely related to amoebas than to plants, and plants are more closely related to the SAR supergroup of protists than to animals or fungi. [citation needed] Animals and fungi are both heterotrophs, unlike plants, and while fungi are sessile like plants, there are also sessile animals.
Excavates were formerly considered to be included in the now obsolete Protista kingdom. [6] They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged (they have a distinctive ultrastructural identity). [4] They are considered to be a basal flagellate lineage. [7]