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The taxon Monera was first proposed as a phylum by Ernst Haeckel in 1866. Subsequently, the phylum was elevated to the rank of kingdom in 1925 by Édouard Chatton. The last commonly accepted mega-classification with the taxon Monera was the five-kingdom classification system was established by Robert Whittaker in 1969.
Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. [16] This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. [ 13 ]
There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, and species. In addition, domain (proposed by Carl Woese ) is now widely used as a fundamental rank, although it is not mentioned in any of the nomenclature codes, and is a synonym for dominion ( Latin : dominium ), introduced by Moore in 1974.
The total number of undescribed organisms is unknown, but marine microbial species alone could number 20,000,000. [12] For this reason, the number of quantified species will always lag behind the number of described species, and species contained in these lists tend to be on the K side of the r/K selection continuum.
A small number of scientists include a sixth kingdom, Archaea, but do not accept the domain method. [ 68 ] Thomas Cavalier-Smith , who published extensively on the classification of protists , in 2002 [ 71 ] proposed that the Neomura , the clade that groups together the Archaea and Eucarya , would have evolved from Bacteria, more precisely from ...
The most commonly accepted definition is the polyphasic species definition, which takes into account both phenotypic and genetic differences. [90] However, a quicker diagnostic ad hoc threshold to separate species is less than 70% DNA–DNA hybridisation, [ 91 ] which corresponds to less than 97% 16S DNA sequence identity. [ 92 ]
The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. [1] [2] [3] About 14% of these had been described by 2011. [3] All species (except viruses) are given a two-part name, a "binomial". The first part of a binomial is the genus to which the species belongs.
A megadiverse country is one of a group of nations that harbours the majority of Earth's species and high numbers of endemic species. Conservation International identified 17 megadiverse countries in 1998, [1] [2] all of which are located at least partially in tropical or subtropical regions. Megadiversity means exhibiting great biodiversity.