Talking about fauna

Troglofauna[edit]
Main article: Troglofauna

The microscopic cave snail Zospeum tholussum, found at depths of 743 to 1,392 m (2,438 to 4,567 ft) in the Lukina Jama–Trojama cave system of Croatia, is completely blind with a translucent shell

Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include spiders, 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 of wings and longer appendages.
Xenofauna[edit]
Main article: Extraterrestrial life
Xenofauna, theoretically, are alien organisms that can be described as animal 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 like astronomy, astrobiology, biochemistry, evolutionary biology, science fiction, and philosophy.