Olm

The olm, or proteus (Proteus anguinus), is a blind amphibian endemic to the subterranean waters of caves of the Dinaric karst of Central and Southeastern Europe. It lives in the waters that flow underground through this extensive limestone region, including waters of the Soča river basin near Trieste, Italy, through to southern Slovenia, southwestern Croatia, and Herzegovina. The olm is the only species in the Proteus genus, the only European species of the Proteidae family, and the only cave-dwelling chordate found only in Europe. It is also occasionally called the "human fish" by locals because of its skin color, similar to that of white people (translated literally from Slovene: človeška ribica and Croatian: čovječja ribica), as well as "cave salamander" or "white salamander." In Slovenia, it is also known by the name močeril, which translates as "the one that burrows into wetness."

This animal is most notable for its adaptations to a life of complete darkness in its underground habitat. The olm's eyes are undeveloped, leaving it blind, while its other senses, particularly those of smell and hearing, are acutely developed. It also lacks any pigmentation in its skin. In contrast to most amphibians, the olm is entirely aquatic, and it eats, sleeps, and breeds underwater. It has three toes on its forelimbs, but two toes on its hind feet. It also exhibits neoteny, retaining larval characteristics like external gills into adulthood, like the American amphibians, the axolotl and the mud puppy.