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2 kingdoms 3 kingdoms — 4 kingdoms: 5 kingdoms: 6 kingdoms — 8 kingdoms: 6 kingdoms: 7 kingdoms — Protista: ... Three domains Five Dominiums [57] Five kingdoms ...
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
It was introduced in the three-domain system of taxonomy devised by Carl Woese, Otto Kandler and Mark Wheelis in 1990. [1] According to the domain system, the tree of life consists of either three domains, Archaea, Bacteria, and Eukarya, [1] or two domains, Archaea and Bacteria, with Eukarya included in Archaea.
Since then, various life forms have been moved into three new kingdoms: Monera, for prokaryotes (i.e., bacteria); Protista, for protozoans and most algae; and Fungi. This five-kingdom scheme is still far from the phylogenetic ideal and has largely been supplanted in modern taxonomic work by a division into three domains: Bacteria and Archaea ...
Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya. The International Code of Zoological Nomenclature defines rank as: "The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank ...
As advances in microscopy made the classification of microorganisms possible, the number of kingdoms increased, five- and six-kingdom systems being the most common. Domains are a relatively new grouping. First proposed in 1977, Carl Woese's three-domain system was not generally accepted until later. [69]
By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Protozoa, Fungi, Plantae (including red and green algae), Chromista, and Bacteria. [44] Five of Cavalier-Smith's kingdoms are classified as eukaryotes as shown in the following scheme: Eubacteria; Neomura. Archaebacteria; Eukaryotes. Kingdom Protozoa
Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes. The two-empire system (two-superkingdom system) was the top-level biological classification system in general use from the early 20th century until the establishment of the three-domain system (which itself is currently being challenged by the two-domain system).