Animalia is a kingdom that appeared during the Precambrian era, and is the most successful kingdom in Earth with more species than any other kingdom. Animals have been around since the Cryogenian Period. Animals are also referred to as Metazoans.
Characteristics of metazoans include eukaryotic cells; unikonta, which are amoebozoa, fungi, animals, and several flagellate eukaryotes (the choanoflagellates); opisthokonta, which are fungi and animals; holozoa, the closest single-celled relatives of animals; and filozoa, the animals and their closest single-celled relatives. After the Cambrian Explosion, the metazoans greatly diversified and resulted in various invertebrates, fish, amphibians, reptiles, birds, and mammals.
