The olm (Proteus anguinus) is a rare amphibian with an unusual appearance, shaped by several million years of living in dark, subterranean caves in central Europe. Its skin lacks pigment, giving its body a white, pasty appearance. It also has a pink hue due to blood capillaries near the skin, and as its translucency shows the contours of the internal organs. This strange fleshy skin led to this species' common name, the human fish, as people thought this bizarre amphibian resembled a small human. This cave dwelling amphibian's four limbs are short and feeble, and its eyes are so poorly developed that it is blind. Its head is elongated with a round snout, and on each side of the head there are three distinctive scarlet gill tufts that are used in respiration, although adults develop lungs as well. Male olms are smaller than females, and can be distinguished from females during breeding season by their larger cloaca. As it spends its entire life in darkness, the olm has very poorly developed eyes and is blind. The olm does not undergo a clear metamorphosis and retains many juvenile features, such as gills, throughout its life. The olm is long-lived, potentially reaching up to 58 years of age.