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Etymology
The word "animal" comes from the Latin word animalis (meaning with soul, from anima, soul). In everyday colloquial usage, the word usually refers to non-human animals.[1]Frequently, only closer relatives of humans such as mammals and other vertebrates are meant in colloquial use.[2] The biological definition of the word refers to all members of the kingdomAnimalia, encompassing creatures ranging from insects to humans.[3]

Characteristics
Animals have several characteristics that set them apart from other living things. Animals are eukaryoticand mostly multicellular,[4] which separates them from bacteria and most protists. They are heterotrophic,[5] generally digesting food in an internal chamber, which separates them fromplants and algae.[6] They are also distinguished from plants, algae, and fungi by lacking rigid cell walls.[7] All animals are motile,[8] if only at certain life stages. In most animals, embryospass through a blastula stage, which is a characteristic exclusive to animals.

Structure
With a few exceptions, most notably the sponges (Phylum Porifera) and Placozoa, animals havebodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals. Typically, there isalso an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general.All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells,bones, and spicules. During development, it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other
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