In biological classification, the relative level of a group of organisms is classified into specific groups on the basis of observable characteristics. These groups are called taxonomic ranks or categories.
Taxonomic hierarchy is the system of arrangement of taxonomic categories in descending order. It was introduced by Linnaeus in 1751, who initially proposed five categories (class, order, genus, species and variety).
However, 'variety' was obliterated and four new categories were introduced. Thus, the seven obligate categories in descending order are kingdom, phylum or division, class, order, family, genus and species.
The placement of individuals or organisms in taxonomic categories is determined by their specific similar characters, dissimilarities, complexity and evolutionary relationships.
Thus, the seven obligate categories in descending order are kingdom, phylum or division, class, order, family, genus and species.
But with the increasing number of organisms, it becomes difficult to adjust them to the traditional basic categories. So, intermediate categories have been created by splitting the basic categories and adding prefixes like “super” or “sub”. For example, sub-phylum, sub-species, etc.