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In 1987, Cavalier-Smith introduced a classification divided into two superkingdoms (Prokaryota and Eukaryota) and seven kingdoms, two prokaryotic kingdoms (Eubacteria and Archaebacteria) and five eukaryotic kingdoms (Protozoa, Chromista, Fungi, Plantae and Animalia). [48]
The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach: Kingdoms such as Protozoa represent grades rather than clades, and so are rejected by phylogenetic classification systems.
Cavalier-Smith's first major classification system was the division of all organisms into eight kingdoms. In 1981, he proposed that by completely revising Robert Whittaker's Five Kingdom system, there could be eight kingdoms: Bacteria, Eufungi, Ciliofungi, Animalia, Biliphyta, Viridiplantae, Cryptophyta, and Euglenozoa.
The last commonly accepted mega-classification with the taxon Monera was the five-kingdom classification system was established by Robert Whittaker in 1969. Under the three-domain system of taxonomy , introduced by Carl Woese in 1977, which reflects the evolutionary history of life, the organisms found in kingdom Monera have been divided into ...
1938 [5] [6] Whittaker 1969 [7] Woese et al. 1977 [8] [9] Woese et al. 1990 [10] Cavalier-Smith 1993 [11] [12] [13] Cavalier-Smith 1998 [14] [15] [16] Ruggiero et al. 2015 [17] — — 2 empires: 2 empires: 2 empires: 2 empires: 3 domains: 3 superkingdoms 2 empires: 2 superkingdoms: 2 kingdoms 3 kingdoms — 4 kingdoms: 5 kingdoms: 6 kingdoms ...
Linnaeus 1735 [1] Haeckel 1866 [2] Chatton 1925 [3] Copeland 1938 [4] Whittaker 1969 [5] Woese et al. 1990 [6] Cavalier-Smith 1998, [7] 2015 [8] 2 kingdoms 3 kingdoms 2 empires: 4 kingdoms: 5 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.
An example is Lithobates (Aquarana) catesbeianus, which designates a species that belongs to the genus Lithobates and the subgenus Aquarana. [15] A subspecies has a name composed of three parts (a trinomial name or trinomen): generic name + specific name + subspecific name; for example Canis lupus italicus. As there is only one possible rank ...