The kingdom Monera included bacteria and cyanobacteria. Classification systems change when technologies such as DNA sequencing provide new information about the relationship between organisms. A three-domain system consisting of Bacteria, Archaea and Eukarya supplanted the five-kingdom system, and Monera is obsolete.
One functional classification system divides organisms by their cell types rather than their genomes. Bacteria belong to the prokaryotes, distinguished by the lack of a nucleus and membrane-enclosed organelles in their cells. Most prokaryotes are single-celled organisms only visible under a microscope. Eukaryotes include protists, fungi, plants and animals. Archaea are prokaryotes that share some characteristics with eukaryotes, including similar genes.