Etymology
The word animal comes from the Latin noun animal of the same meaning, which is itself derived from Latin animalis 'having breath or soul'.[6] The biological definition includes all members of the kingdom Animalia.[7] In colloquial usage, the term animal is often used to refer only to nonhuman animals.[8][9][10][11] The term metazoa is derived from Ancient Greek μετα meta 'after' (in biology, the prefix meta- stands for 'later') and ζῷᾰ zōia 'animals', plural of ζῷον zōion 'animal'.[12][13]
Characteristics
Animals have several characteristics that they share with other living things. Animals are eukaryotic, multicellular, and aerobic, as are plants and fungi.[14] Unlike plants and algae, which produce their own food,[15] animals cannot produce their own food[16][17] a feature they share with fungi. Animals ingest organic material and digest it internally.[18]
Structural features
Animals have structural characteristics that set them apart from all other living things:
- cells surrounded by an extracellular matrix[19] composed of
- collagen[20] and
- elastic glycoproteins[19][21]
- motility[22] i.e. able to spontaneously move their bodies during at least part of their life cycle.
- a blastula stage during embryonic development[23]
Typically, there is an internal digestive chamber with either one opening (in Ctenophora, Cnidaria, and flatworms) or two openings (in most bilaterians).[24]