Size of proteome of each species: The X-axis is the index of the number of each species, while the Y-axis is the number of proteins. Filled circles represent the size of the proteome of each species. Filled squares indicate the taxonomy of archaea with similar species together and on same level. (1), (3)-(5) indicate species in four phyla: Crenarchaeota, Korarchaeota, Nanoarcgaeota, and Thaumarchaeota. (2.1) - (2.8) are eight different classes in the phylum of Euryarchaeota as shown in Table. 1.