Olm (Proteus anguinus)
The olm, or proteus, is the only cave-dwelling chordate species found in Europe. In contrast to many amphibians, it is entirely aquatic, and it eats, sleeps, and breeds underwater.
Living in caves found in Dinaric Alps, it is endemic to the waters that flow underground through extensive limestone of karst of Central and Southeastern Europe, specifically the southern Slovenia, the Soča river basin near Trieste, Italy, southwestern Croatia, and Herzegovina.
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. 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.
The olm’s body is snakelike, 20–30 cm (8–12 in) long, with some specimens reaching up to 40 centimetres (16 in). The olm is extremely vulnerable to changes in its environment due to its adaptation to the specific conditions in caves.
On the IUCN Red List, the olm is listed as vulnerable because of its fragmented and limited distribution and ever-decreasing population.