|Image: Niphargus from the Falkensteiner Höhle, Germany.|
Troglobionts or Eutroglobionts are animals that live in caves and are unable to live outside of it. Troglobionts usually have troglomorphic adaptions, which means they have adapted to the special environment. This is generally the reason why they would not survive outside.
Typical adaptions to the cave environment are intensification of useful senses: smell, touch, and hear. Many troglobites have long antennas, can feel very good and even feel vibrations in air and rock and thus sense moving objects. Smell is also a usefull sense, especially for animals living in the water.
On the other hand there is the loss of useless senses. As there is absolutely no light, sight is the first which is abandoned. Sometime even the eyes get lost. Or they exist but cannot see any more.
And finally there are passive adaptions, like the loss of skin pigmentation. Troglobites are pale, most of them are white or transparent. Blood shines through the transparent skin, colouring it pink or is transparent too. This is no usefull adaption, it is caused simply by a lack of necessity, of stimulants, but it makes the return to the surface impossible. The troglobite would die very soon from the ultraviolet light of the sun. Even short exposure to sunlight might be lethal, think about the worst sunburn ever.