# Animal By [KlOP](https://paragraph.com/@klop) · 2023-05-30 --- **Animals** are [multicellular](https://en.wikipedia.org/wiki/Multicellular), [eukaryotic](https://en.wikipedia.org/wiki/Eukaryotic) organisms in the [biological kingdom](https://en.wikipedia.org/wiki/Kingdom_\(biology\)) **Animalia**. With few exceptions, animals [consume organic material](https://en.wikipedia.org/wiki/Heterotroph), [breathe oxygen](https://en.wikipedia.org/wiki/Cellular_respiration#Aerobic_respiration), are [able to move](https://en.wikipedia.org/wiki/Motility), can [reproduce sexually](https://en.wikipedia.org/wiki/Sexual_reproduction), and grow from a hollow sphere of cells, the [blastula](https://en.wikipedia.org/wiki/Blastula), during [embryonic development](https://en.wikipedia.org/wiki/Embryonic_development). As of 2022, 2.16 million [living](https://en.wikipedia.org/wiki/Extant_taxon) animal [species](https://en.wikipedia.org/wiki/Species) have been [described](https://en.wikipedia.org/wiki/Species_description)—of which around 1.05 million are [insects](https://en.wikipedia.org/wiki/Insecta), over 85,000 are [molluscs](https://en.wikipedia.org/wiki/Mollusca), and around 65,000 are [vertebrates](https://en.wikipedia.org/wiki/Vertebrate)—but it has been estimated there are around 7.77 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have [complex interactions](https://en.wikipedia.org/wiki/Ecology) with each other and their environments, forming intricate [food webs](https://en.wikipedia.org/wiki/Food_web). The scientific study of animals is known as [zoology](https://en.wikipedia.org/wiki/Zoology). nft://137/0xe4bDcC11A6b9EB941FE3A761D174714Eb626d44a/?showBuying=true&showMeta=true Most living animal species are in [Bilateria](https://en.wikipedia.org/wiki/Bilateria), a [clade](https://en.wikipedia.org/wiki/Clade) whose members have a [bilaterally symmetric](https://en.wikipedia.org/wiki/Symmetry_in_biology#Bilateral_symmetry) [body plan](https://en.wikipedia.org/wiki/Body_plan). The Bilateria include the [protostomes](https://en.wikipedia.org/wiki/Protostomes), containing animals such as [nematodes](https://en.wikipedia.org/wiki/Nematode), [arthropods](https://en.wikipedia.org/wiki/Arthropod), [flatworms](https://en.wikipedia.org/wiki/Flatworm), [annelids](https://en.wikipedia.org/wiki/Annelid) and molluscs, and the [deuterostomes](https://en.wikipedia.org/wiki/Deuterostomes), containing the [echinoderms](https://en.wikipedia.org/wiki/Echinoderm) and the [chordates](https://en.wikipedia.org/wiki/Chordate), the latter including the vertebrates. Life forms interpreted as early animals were present in the [Ediacaran biota](https://en.wikipedia.org/wiki/Ediacaran_biota) of the late [Precambrian](https://en.wikipedia.org/wiki/Precambrian). Many modern animal [phyla](https://en.wikipedia.org/wiki/Phylum) became clearly established in the [fossil record](https://en.wikipedia.org/wiki/Fossil_record) as [marine species](https://en.wikipedia.org/wiki/Marine_life) during the [Cambrian explosion](https://en.wikipedia.org/wiki/Cambrian_explosion), which began around 539 million years ago. 6,331 groups of [genes](https://en.wikipedia.org/wiki/Gene) common to all living animals have been identified; these may have arisen from a single [common ancestor](https://en.wikipedia.org/wiki/Animal#Phylogeny) that lived [650 million years ago](https://en.wikipedia.org/wiki/Cryogenian). Historically, [Aristotle divided animals](https://en.wikipedia.org/wiki/Aristotle%27s_biology) into those with blood and those without. [Carl Linnaeus](https://en.wikipedia.org/wiki/Carl_Linnaeus) created the first hierarchical [biological classification](https://en.wikipedia.org/wiki/Taxonomy_\(biology\)) for animals in 1758 with his [_Systema Naturae_](https://en.wikipedia.org/wiki/Systema_Naturae), which [Jean-Baptiste Lamarck](https://en.wikipedia.org/wiki/Jean-Baptiste_Lamarck) expanded into 14 phyla by 1809. In 1874, [Ernst Haeckel](https://en.wikipedia.org/wiki/Ernst_Haeckel) divided the animal kingdom into the multicellular **Metazoa** (now [synonymous](https://en.wikipedia.org/wiki/Synonym_\(taxonomy\)) with Animalia) and the [Protozoa](https://en.wikipedia.org/wiki/Protozoa), single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as [molecular phylogenetics](https://en.wikipedia.org/wiki/Molecular_phylogenetics), which are effective at demonstrating the [evolutionary](https://en.wikipedia.org/wiki/Evolution) relationships between [taxa](https://en.wikipedia.org/wiki/Taxon). [Humans](https://en.wikipedia.org/wiki/Human) make [use of many animal species](https://en.wikipedia.org/wiki/Human_uses_of_animals), such as for food (including [meat](https://en.wikipedia.org/wiki/Meat), [milk](https://en.wikipedia.org/wiki/Milk), and [eggs](https://en.wikipedia.org/wiki/Egg)), for materials (such as [leather](https://en.wikipedia.org/wiki/Leather) and [wool](https://en.wikipedia.org/wiki/Wool)), as [pets](https://en.wikipedia.org/wiki/Pet), and as [working animals](https://en.wikipedia.org/wiki/Working_animal) including for transport. [Dogs](https://en.wikipedia.org/wiki/Dog) have been [used in hunting](https://en.wikipedia.org/wiki/Hunting_dog), as have [birds of prey](https://en.wikipedia.org/wiki/Falconry), while many terrestrial and [aquatic animals](https://en.wikipedia.org/wiki/Aquatic_animal) were hunted for sports. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion. Etymology --------- The word "animal" comes from the Latin [_animalis_](https://en.wiktionary.org/wiki/animalis#Latin), meaning 'having breath', 'having soul' or 'living being'.[\[4\]](https://en.wikipedia.org/wiki/Animal#cite_note-4) The biological definition includes all members of the kingdom Animalia.[\[5\]](https://en.wikipedia.org/wiki/Animal#cite_note-americanheritage_animal-5) In colloquial usage, the term _animal_ is often used to refer only to nonhuman animals.[\[6\]](https://en.wikipedia.org/wiki/Animal#cite_note-6)[\[7\]](https://en.wikipedia.org/wiki/Animal#cite_note-7)[\[8\]](https://en.wikipedia.org/wiki/Animal#cite_note-8)[\[9\]](https://en.wikipedia.org/wiki/Animal#cite_note-9) The term "metazoa" is derived from the Ancient Greek μετα (_meta_, meaning "later") and ζῷᾰ (_zōia_, plural of ζῷον _zōion,_ meaning animal).[\[10\]](https://en.wikipedia.org/wiki/Animal#cite_note-10)[\[11\]](https://en.wikipedia.org/wiki/Animal#cite_note-11) --- *Originally published on [KlOP](https://paragraph.com/@klop/animal)*