February 3, 2011 : Olm

Olm

The Olm, or Proteus (Proteus anguinus), is a blind amphibian endemic to the subterranean waters of caves of the Dinaric karst of southern Europe. It lives in the waters that flow underground through this extensive limestone region including waters of the Soča river basin near Trieste in Italy, through to southern Slovenia, southwestern Croatia, and Herzegovina. The olm is the only species in its genus Proteus, the only European species of the family Proteidae, and the only European exclusively cave-dwelling chordate. 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 3 toes on its forelimbs, but 2 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.

The olm's body is snakelike, 20–30 cm (8–12 in) long, with some specimens reaching up to 40 centimetres (16 in). The trunk is cylindrical, uniformly thick, and segmented with regularly spaced furrows at the myomeretail is relatively short, laterally flattened, and surrounded by a thin fin. The limbs are small and thin, with a reduced number of digits compared to other amphibians: the front legs have three digits instead of the normal four, and the rear have two digits instead of five. Its body is covered by a thin layer of skin, which contains very little of the pigment riboflavin, making it yellowish-white or pink in color. The internal organs can be seen shining through on the abdominal part of the body. The resemblance in color to that of white humans is the reason why the borders. The Proteus is called human fish in some languages. However, the olm's skin retains the ability to produce melanin. When exposed to light, it will gradually turn dark, and in some cases the larvae are also colored. Its pear-shaped head ends with a short, dorsoventrally flattened snout. The mouth opening is small, with tiny teeth forming a sieve to keep larger particles inside the mouth. The nostrils are so small as to be imperceptible, but are placed somewhat laterally near the end of the snout. The regressed eyes are covered by a layer of skin. The olm breathes with external gills that form two branched tufts at the back of the head. They are red in color because the oxygen-rich blood shows through the non-pigmented skin. The olm also has rudimentary lungs, but their role in respiration is only accessory. The sexes are very similar in appearance, with males having a somewhat thicker cloaca than females.