Monera

Monera


Scanning electron micrograph of Escherichia coli
S
Monera (/məˈnɪərə/ mə-neer-ə) is one of the five taxonomic groups in the superseded five-kingdom classification system which was established by Robert Whittaker in 1946. The kingdom Monera contains unicellular organisms without a nucleus (i.e., a prokaryotic cell organization), such as bacteria.
Under the three-domain system of taxonomy, which was established in 1990 and reflects the evolutionary history of life as currently understood, the organisms found in kingdom Monera have been divided into two domains, Archaea and Bacteria (with Eukarya as the third domain). Furthermore the taxon Monera is paraphyletic. The term "moneran" is the informal name of members of this group and is still sometimes used (as is the term "prokaryote") to denote a member of either domain.
Despite most bacteria being classified under Monera, the bacterial phylum Cyanobacteria (the blue-green algae) was not classified under Monera, but under Plantae given the ability of its members to photosynthesise.

1 History

Traditionally the natural world was classified as animal, vegetable, or mineral as in Systema Naturae. After the discovery of microscopy, attempts were made to fit microscopic organisms into either the plant or animal kingdoms. In 1676, Antonie van Leeuwenhoek discovered bacteria and called them "animacules," assigning them to the class Vermes of the Animalia. Due to the limited tools — the sole references for this group were shape, behaviour, and habitat — the description of genera and their classification was extremely limited, which was accentuated by the perceived lack of importance of the group.
Ten years after The Origin of Species by Darwin, in 1866 Ernst Haeckel, a supporter of evolution, proposed a three-kingdom system which added the Protista as a new kingdom that contained most microscopic organisms. One of his eight major divisions of Protista was composed of the monerans (called Moneres in German) and defines them as completely structureless and homogeneous organisms, consisting only of a piece of plasma. Haeckel's Monera included not only bacterial groups of early discovery but also several small eukaryotic organisms; in fact the genus Vibrio is the only bacterial genus explicitly assigned to the phylum, while others are mentioned indirectly, which has led Copeland to speculate that Haeckel considered all bacteria to belong to the genus Vibrio, ignoring other bacterial genera.[7] One notable exception were the members of the modern phylum Cyanobacteria, such as Nostoc, which were placed in the phylum Archephyta of Algae (vide infra: Blue-green algae).
The Neolatin noun Monera and the German noun Moneren/Moneres are derived from the ancient Greek noun moneres (μονήρης) which Haeckel states to mean "simple", however it actually means "single, solitary". Haeckel also describes the protist genus Monas in the two pages about Monera in his 1866 book. The informal name of a member of the Monera was initially moneron, but later moneran was used.
Due to its lack of features, the phylum was not fully subdivided, but the genera therein were divided into two groups:
die Gymnomoneren (no envelope [sic.]): Gymnomonera
Protogenes — such as Protogenes primordialis, an unidentified amaeba (eukaryote) and not a bacterium
Protamaeba — an incorrectly described/fabricated species
Vibrio — a genus of comma-shaped bacteria first described in 1854
Bacterium — a genus of rod-shaped bacteria first described in 1828. Haeckel does not explicitly assign this genus to the Monera.
Bacillus — a genus of spore-forming rod-shaped bacteria first described in 1835 Haeckel does not explicitly assign this genus to the Monera.
Spirochaeta — thin spiral-shaped bacteria first described in 1835 Haeckel does not explicitly assign this genus to the Monera.
Spirillum — spiral-shaped bacteria first described in 1832Haeckel does not explicitly assign this genus to the Monera.
etc.: Haeckel does provide a comprehensive list.
die Lepomoneren (with envelope): Lepomonera
Protomonas — identified to a synonym of Monas, a flagellated pro