Animal
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Infrakingdom Eumetazoa
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The animals are the group of living organisms classified in the kingdom Animalia. They are all multicellular eukaryotes, and also ingest their food and move by their own power at some point in their life cycle.[1]
Etymology
The word animal comes from the Latin animale, which is derived from anima, meaning "vital breath".
Characteristics
Cells
Animals are eukaryotic, meaning that they are comprised of cells which contain a nucleus. Unlike plants and fungi, their cells lack cell walls. Unlike bacteria, archaea and most protists, they are also usually multicellular.[1]
Food and energy
Animals are heterotrophs: they obtain nutrients by ingesting food from outside, generally digesting food in an internal chamber. This is unlike plants, algae, and other autotrophs, which do not ingest food. They are consumers that often occupy the higher levels of food chains in many ecosystems.[1] They obtain their food in a dazzling array of methods: for instance, rancher ants tend aphids and harvest the sugar that they secrete.[2]
Methods of obtaining food
Animals typically obtain food in two ways. Predation is a biological interaction where a heterotroph, called the predator, obtains food by consuming the cells of another organism, called the prey. Herbivores are predators that primarily consume autotrophs, carnivores are predators that primarily consume heterotrophs, and omnivores are predators that consume both autotrophs and heterotrophs.
The other major method of obtaining food is detritivory, where a heterotroph consumes food from detritus: dead organic matter. Detritivores recycle nutrients and are thus important in decomposition.
Methods of feeding
The methods of feeding that animals use may be grouped into four general tactics. Suspension feeding, or filter feeding, filters out and concentrates food particles suspended in water or air, such as a baleen whale filtering out plankton. Deposit feeding swallows a substrate and ingests the microorganisms, detritus, and other cells within the substrate, such as an earthworm eats through soil. Fluid feeding sucks fluids such as body fluids from plants and animals, such as a butterfly drinking a flower's nectar. Mass feeding, or bulk feeding, eats chunks of flesh from prey into the mouth, such as a snail eating pieces of leaves.
Movement
Animals are motile during at least one point of their life cycle. They move by a large variety of methods: swimming, crawling on a substrate, walking, or flying.[1]