Animalea are the largest most diverse of all the kingdoms. Two million species have been identified so far and species are still being discovered today. Animals are heterotrophs meaning they feed on other organisms for energy. They are highly mobile unlike the other kingdoms. They reproduce sexually and give birth to live young or young in eggs, such as snakes and birds. Animals are also equipped with sense organs that allow them to react quickly to changes. Animals are classified into divisions and subdivisions. First is the phylum, then the class, order, family, and genera. Then the genus is subdivided into species with common characteristics that can breed together. 98% of animals have no backbone, such as jellyfish, called invertebrates. Mammals, fish, birds, anphibians, and reptiles are called vertebrates. Known to exist some 1.2 billion years ago the history is still incomplete.