Most olms lack visible eyes, as they are covered with skin, and they sense their surroundings using receptors, as well as relying on hearing and smell. On the ventral side of the body the skin is translucent and reveals the contours of internal organs. Mudpuppies are dark with large spots and have small eyes.

The skin is usually creamy white, but may have a pinkish hue.

The olm’s have an area of light sensitive specialised cells called ‘melanophores’ on top of their head.

Amphibians (am-FIB-ee-uhns) are vertebrates (VER-teh-brehts), or animals with a … Olms are pale and sightless, although their skin-covered eyes are still sensitive to light, despite spending their entire lives in caves. Olms and mudpuppies are large for salamanders, more than 16 inches (40 centimeters) from the tip of the snout to the tip of the tail.

Olm eyes can only detect the presence of light, but not much else. Darkening of the skin is reversed when it is returned to the darkness. They have incredible sense of smell and hearing and can detect detect light and electrical or magnetic fields.” Weldt added that female olms only reproduce once every six to seven years. Olms have short frilly gills; a long eel-like body, that moves in similar ways; as well as four small legs, while the back legs have two digits and the front have three. Thus, these little gill-adorned weirdos are essentially blind, ... And it's not like they can't move - some olms have easily fled from nosy scientists, by wiggling their way through tens of metres of water. Olms begin life with well developed eyes, but by the time they reach adulthood those eyes have retreated beneath the skin and the animal is blind. To compensate for the lack of sight, the olm has other more acute senses that allow them to hunt in the dark.

Olms also begin life with black skin, but lose their color as they grow into adulthood, although dark pigmentation can be induced by exposure to light (prolonged exposure to light is lethal to olms). “They have transparent white skin that also covers their eyes, but they don’t need to see.
Olms and mudpuppies spend their entire lives in water, never making the move to land the way many amphibians do.

Interestingly, larvae’s eyes develop normally until they are about 4 months old when the development stops and the eyes start to atrophy. Olms hunt their prey in the absolute dark and have developed a powerful sensory system of smell, taste, hearing and electrosensitivity. When exposed to light, the skin turns dark violet to black.

Its eyes are very small and do not even breach the skin.