The amphibian that is blind and lives exclusively in underwater caves is the olm.
The olm, Proteus anguinus, is a slender salamander native to underground waters in the Dinaric Alps of southeastern Europe. It spends its entire life underwater, including feeding, sleeping, and breeding. Its undeveloped eyes are covered by skin, making it functionally blind, while its senses of smell, hearing, and sensitivity to water movement help it navigate and locate prey.
Olms retain several larval features into adulthood, a condition called neoteny. These include feathery external gills, a long sinuous body, and tiny limbs. Their usually pale, pinkish coloration reflects life in darkness; a darker form, sometimes called the black olm, also exists.
A common mix-up is the axolotl, another aquatic salamander that retains external gills. Axolotls generally have visible eyes and come from Mexican lakes, whereas olms are cave-adapted animals of Europe. The olm was described scientifically in 1768, after earlier reports compared it with a cave dragon.