Light and shade

BBC Wildlife Magazine - - Olms -

The olm is renowned for be­ing a pale crea­ture lack­ing skin pig­men­ta­tion. How­ever, not all olms are the same. In fact, there is one recog­nised sub­species, Pro­teus an­gui­nus parkelj, the black olm, which can be dark brown as well as black. Dis­cov­ered in 1986, the black olm is re­stricted to an area smaller than 100sq km near Crnomeljˇ in Slove­nia.

As well as hav­ing pig­men­ta­tion, the black olm has a num­ber of other dif­fer­ences to the nom­i­nate sub­species ( P. a. an­gui­nus). Its head is slightly shorter, with strong jaw mus­cles, and it has shorter legs. Though its body length is slightly longer (it has 34–35 ver­te­brae com­pared to 29–32 in the nom­i­nate sub­species), its tail is shorter, in pro­por­tion.

In ad­di­tion, rather than hav­ing com­pletely re­gressed eyes, the eyes of the black olm de­velop al­most nor­mally, and have prin­ci­pal rods, and both red­sen­si­tive and blue-sen­si­tive cones.

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