Monera is a kingdom that contains unicellular organisms with no nucleus, such as bacteria. It was first proposed as a phylum in 1866 and later elevated to kingdom status in 1925. The last major taxonomy to include the kingdom Monera was the five-kingdom system established in 1969. Protists are a diverse group of eukaryotic microorganisms belonging to the kingdom Protista. There have been attempts to remove this kingdom from taxonomy but it remains in use. Molecular evidence has redefined protists as diverse, unrelated phyla with different life cycles, trophic levels, and cellular structures rather than having much in common. They are unicellular or multicellular without specialized tissues.