Animal

Animals are mainly multicellular eukaryotic organisms of the Kingdom Animalia. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also heterotrophs, meaning they must ingest other organisms for sustenance. Animals are classified into three general groups, based on how they feed. Parasites feed off of other animals, either by consuming some of the nutrition that their host takes in, or by stealing already-absorbed nutrition. More than three-quarters of all animals belong to this group. Herbivorous animals feed on plants, while carnivorous ones feed on other animals.

Most extant animal phyla appeared in the Cambrian Explosion.

Classification
Animals are a form of organism; perhaps the most complex organisms on Earth. They are eukaryotes (their cells have neuclei) and most are multicellular; however a few animal groups, such as the amoebids, are unicellular, bacterium-like, and feed mainly on viruses. Along with the metazoans, animals are grouped in the Filozoa, the group that contains all organisms capable of independant movement.

Etymology


The word "animal" comes from the Latin word animal (meaning with soul, from anima, soul). In everyday colloquial usage, the word usually refers to non-human animals. Frequently only closer relatives of humans such as vertebrates or mammals are meant in colloquial use. The biological definition of the word refers to all members of the Kingdom Animalia, encompassing creatures ranging from sponges to humans.

History
The earliest animal fossils