|The Linnaean System|
|In the Linnaean system (and taxonomic systems based on it), a Class is the taxonomic category between Phylum and Order. A class is a major group of organisms, e.g. Mammalia, Reptilia, Gastropoda, Insecta, etc that contains a large number of different sublineages, but have shared characteristics in common (e.g. warm-blooded, fur, mammary glands in female in the case of mammals, six legs and three body parts in the case of Insects, etc). As with all the groupings whether a group of organisms ranks as a class or not is a subjective decision, although usually based on the traditional status of that group in earlier literature. The cladistic revolution has caused a reappraisal of these rankings, and rejection or modification of many of these rankings.|
Originally Linnaeus divided the Animal Kingdom into six classes.
Many more have been proposed since then...