"The system of grottos is rich in speleofauna and a major habitat for Microtus nivalis and the endemic Proteas anguinus" (AB ev) ("The olm or proteus (Proteus anguinus) is an aquatic salamander which is the only species in the genus Proteus of the family Proteidae and the only exclusively cave-dwelling chordate species found in Europe;" - Wiki)

Crit X: "considered one of world’s most important biodiversity hotspots for cave-dwelling fauna"

"The flora and fauna of Mammoth Cave is the richest cave-dwelling wildlife known, with more than 130 species within the cave system." (OUV)