Linnaean classification

Taxonomy classifies organisms into groups. There are two taxonomic approaches: the Linnaean system classifies life according to an eight level hierarchy based on features other than phylogenomics (cladistics).

The three-domain system is an addition to the Linnaean system biological classification introduced by Carl Woese et al. in 1977[48][49] that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea). Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each arose separately from an ancestor with poorly developed genetic machinery, often called a progenote. To reflect these primary lines of descent, he treated each as a domain, divided into several different kingdoms. The term "domain" was adopted in 1990.[49]

Animals are thus classified under the domain Eukaryota. The Linnaean hierarchy below the kingdom Animalia consists of these groups: phyla, classes, orders, families, genera, and species. All the groups, from domain to species, are called taxa. There are occasional intermediate levels, such as superphyla and subphyla, in special situations. The International Commission on Zoological Nomenclature (ICZN) determines what names are valid for any taxon in the family, genus, and species group. It has additional but more limited provisions on names in higher ranks.