Monera (
Greek - μονήρης (monḗrēs), "single", "solitary") ( ) was a
kingdom that contained unicellular organisms with a
prokaryotic cell organization (having no
nuclear membrane), such as bacteria. 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 established by
Robert Whittaker in 1969.