Fauna (pl.:faunae orfaunas) is all of theanimal life present in a particular region or time. The corresponding terms forplants andfungi areflora andfunga, respectively. Flora, fauna, funga and other forms of life are collectively referred to asbiota.Zoologists andpaleontologists usefauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess Shale fauna".Paleontologists sometimes refer to a sequence offaunal stages, which is a series of rocks all containing similar fossils. The study of animals of a particular region is calledfaunistics.

Fauna comes from the nameFauna, a Roman goddess of earth and fertility, the Roman godFaunus, and the related forest spirits calledFauns. All three words are cognates of the name of the Greek godPan, andpanis is theModern Greek equivalent of fauna (πανίς or rather πανίδα).Fauna is also the word for a book that catalogues the animals in such a manner. The term was first used byCarl Linnaeus from Sweden in the title of his 1745^[1] workFauna Suecica.

Cryofauna refers to the animals that live in, or very close to, cold areas.

Cryptofauna is the fauna that exists in protected or concealedmicrohabitats.^[2]

Epifauna, also calledepibenthos, are aquatic animals that live on the bottom substratum as opposed to within it, that is, thebenthic fauna that live on top of the sediment surface at the seafloor.

Infauna arebenthic organisms that live within the bottom substratum of a water body, especially within the bottom-most oceanic sediments, the layer of small particles at the bottom of a body of water, rather than on its surface.Bacteria andmicroalgae may also live in the interstices of bottom sediments. In general, infaunal animals become progressively smaller and less abundant with increasing water depth and distance from shore, whereas bacteria show more constancy in abundance, tending toward one million cells per milliliter of interstitial seawater.

Such creatures are found in the fossil record and includelingulata,trilobites andworms. They made burrows in the sediment as protection and may also have fed upon detritus or the mat of microbes which tended to grow on the surface of the sediment.^[3] Today, a variety of organisms live in anddisturb the sediment. The deepest burrowers are the ghost shrimps (Thalassinidea), which go as deep as 3 metres (10 ft) into the sediment at the bottom of the ocean.^[4]

Limnofauna refers to the animals that live in fresh water.

Macrofauna arebenthic or soil organisms which are retained on a 0.5 mm sieve. Studies in the deep sea define macrofauna as animals retained on a 0.3 mm sieve to account for the small size of many of the taxa.

Megafauna are large animals of any particular region or time. For example,Australian megafauna.

Meiofauna are smallbenthicinvertebrates that live in both marine and freshwaterenvironments. The termmeiofauna loosely defines a group oforganisms by their size, larger than microfauna but smaller than macrofauna, rather than a taxonomic grouping. One environment for meiofauna is between grains of damp sand (seeMystacocarida).

In practice these are metazoan animals that can pass unharmed through a 0.5–1 mmmesh but will be retained by a 30–45 μm mesh,^[5] but the exact dimensions will vary fromresearcher to researcher. Whether an organism passes through a 1 mm mesh also depends upon whether it is alive or dead at the time of sorting.

Mesofauna are macroscopic soil animals such asarthropods ornematodes. Mesofauna are extremely diverse; considering just the springtails (Collembola), as of 1998, approximately 6,500 species had been identified.^[6]

Microfauna are microscopic or very small animals (usually includingprotozoans and very small animals such asrotifers). To qualify as microfauna, an organism must exhibit animal-like characteristics, as opposed tomicroflora, which are more plant-like.

Stygofauna is any fauna that lives ingroundwater systems or aquifers, such ascaves, fissures andvugs. Stygofauna andtroglofauna are the two types ofsubterranean fauna (based on life-history). Both are associated with subterranean environments – stygofauna is associated with water, and troglofauna with caves and spaces above thewater table. Stygofauna can live within freshwateraquifers and within thepore spaces oflimestone,calcrete orlaterite, whilst larger animals can be found in cave waters and wells. Stygofaunal animals, like troglofauna, are divided into three groups based on their life history - stygophiles, stygoxenes, and stygobites.^[7]

Troglofauna are smallcave-dwellinganimals that haveadapted to their dark surroundings. Troglofauna andstygofauna are the two types ofsubterranean fauna (based on life-history). Both are associated with subterranean environments – troglofauna is associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species includespiders,insects,myriapods and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell.^[8] Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit a lack ofwings and longerappendages.

Xenofauna,theoretically, arealien organisms that can be described asanimal analogues. While no alien life forms, animal-like or otherwise, are known definitively, the concept of alien life remains a subject of great interest in fields likeastronomy,astrobiology,biochemistry,evolutionary biology,science fiction, andphilosophy.

Other terms includeavifauna, which means "bird fauna" andpiscifauna (orichthyofauna), which means "fish fauna".

• Linnaeus, Carolus.Fauna Suecica. 1746

• "Biodiversity of Collembola and their functional role in the ecosystem" (by Josef Rusek; September 1998)