The olm's sensory system is also adapted to life in the subterranean aquatic environment. Sensory organs Ĭave-dwelling animals have been prompted, among other adaptations, to develop and improve non-visual sensory systems in order to orient in and adapt to permanently dark habitats. The olm also has rudimentary lungs, but their role in respiration is only accessory, except during hypoxic conditions. They are red in color because the oxygen-rich blood shows through the non-pigmented skin. The olm breathes with external gills that form two branched tufts at the back of the head. The regressed eyes are covered by a layer of skin. The nostrils are so small as to be imperceptible, but are placed somewhat laterally near the end of the snout. The mouth opening is small, with tiny teeth forming a sieve to keep larger particles inside the mouth. Its pear-shaped head ends with a short, dorsoventrally flattened snout. The white skin color of the olm retains the ability to produce melanin, and will gradually turn dark when exposed to light in some cases the larvae are also colored. 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 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. The tail is relatively short, laterally flattened, and surrounded by a thin fin. The trunk is cylindrical, uniformly thick, and segmented with regularly spaced furrows at the myomere borders. Females grow larger than males, but otherwise the primary external difference between the sexes is in the cloaca region (shape and size) when breeding. The olm's body is snakelike, 20–30 cm (8–12 in) long, with some specimens reaching up to 40 centimetres (16 in), which makes them the largest cave-dwelling animals in the world. The olm as depicted by the French biologist Gaston Bonnier in 1907 In Slovenia, it is called močeril (from * močerъ 'earthworm, damp creepy-crawly' moča 'dampness'). It is also called the "human fish" by locals because of its fleshy skin color (translated literally from Slovene: človeška ribica, Macedonian: човечка рипка, Croatian: čovječja ribica, Bosnian: čovječja ribica Serbian: човечја рибица), as well as "cave salamander" or "white salamander". It may be a variant of the word Molch 'salamander'. The origin of the German Olm or Grottenolm 'cave olm', is unclear. The word olm is a German loanword that was incorporated into English in the late 19th century. It exhibits neoteny, retaining larval characteristics like external gills into adulthood, like some American amphibians, the axolotl and the mudpuppies ( Necturus). It has three toes on its forelimbs, but only two toes on its hind feet. It also lacks any pigmentation in its skin. The olm's eyes are undeveloped, leaving it blind, while its other senses, particularly those of smell and hearing, are acutely developed. This cave salamander is most notable for its adaptations to a life of complete darkness in its underground habitat. It was first mentioned in 1689 by the local naturalist Valvasor in his Glory of the Duchy of Carniola, who reported that, after heavy rains, the olms were washed up from the underground waters and were believed by local people to be a cave dragon's offspring. Introduced populations are found near Vicenza, Italy, and Kranj, Slovenia. Living in caves found in the Dinaric Alps, it is endemic to the waters that flow underground through the extensive limestone bedrock of the karst of Central and Southeastern Europe in the basin of the Soča River ( Italian: Isonzo) near Trieste, Italy, southwestern Croatia, and Bosnia and Herzegovina. In contrast to most amphibians, it is entirely aquatic, eating, sleeping, and breeding underwater. The olm or proteus ( Proteus anguinus) is an aquatic salamander which is the only species in the genus Proteus of the family Proteidae and the only exclusively cave-dwelling chordate species found in Europe the family's other extant genus is Necturus.
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