Two olms (Proteus anguinus), in Postojna Cave, Slovenia.

Description
English: Two olms (Proteus anguinus), in Postojna Cave, Slovenia.
Date December 1999
Author Boštjan Burger
Source: https://commons.wikimedia.org/wiki/File:Proteus_anguinus_Postojnska_Jama_Slovenija.jpg

The olm or proteus (Proteus anguinus) is an aquatic salamander in the family Proteidae, the only exclusively cave-dwelling chordate species found in Europe. In contrast to most amphibians, it is entirely aquatic; it eats, sleeps, and breeds underwater. Living in caves found in the Dinaric Alps, it is endemic to the waters that flow underground through the extensive limestone of the karst of Central and Southeastern Europe, specifically southern Slovenia, the basin of the Soča River (Italian: Isonzo) near Trieste, Italy, southwestern Croatia, and Bosnia and Herzegovina. Order: Caudata, Family: Proteidae, Genus: Proteus, Species: Proteus anguinus Laurenti, 1768.