Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan
becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals
are motile - they can move spontaneously and independently. Animals are heterotrophs - they are dependent on other
organisms (e.g. plants) for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542
million years ago.
The word "animal" comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning vital breath
or soul. In everyday colloquial usage, the word usually refers to non-human animals. The biological definition of the word
refers to all members of the Kingdom Animalia. Therefore, when the word "animal" is used in a biological context, humans
are included.
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