The Strange World of Troglobites | 20 Years of Planet Earth | BBC Earth

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[00:00:00]It takes thousands of generations for eyes to be lost. So these species must have been isolated for a very long time.

[00:00:09]Many caves are like islands cut off from the outside world and from other caves.

[00:00:23]This isolation has resulted in the evolution of some very strange creatures.

[00:00:32]They are the cave specialists, troglobites, animals that never emerge from the caves or see daylight.

[00:00:53]These trogloites from Thailand are possibly the most specialized creatures on Earth, for they live only in cave waterfalls.

[00:01:03]The entire population of these cave angelf fish seems to be restricted to just two small caves.

[00:01:15]It's the same story with other trogler bites. There may well be less than 100 Texas cave salamanders in the wild.

[00:01:39]And the Blelesian white crab is another creature that is unique to just one cave system.

[00:01:51]Living in perpetual darkness, they have all not only lost the pigment in their skin, but also their eyes.

[00:02:00]It takes thousands of generations for eyes to be lost. So these species must have been isolated for a very long time.

[00:02:13]But the blind salamander has other highly developed sensory organs.

[00:02:21]Receptors in the skin detect minute movements in the water made by its prey.

[00:02:33]External gills help it to breathe in water that is particularly low in oxygen.

[00:02:50]The cave angelf fish feed on bacteria in the fast flowing water, keeping their grip with microscopic hooks on their fins.

[00:03:10]Food is often in short supply and trogabites like the crab have to survive on whatever washes into the cave from outside.

[00:03:23]A salamander might not encounter food for several months, so when something does come along, it can't afford to miss it.

[00:03:38]It's astonishing that these extraordinary cave dwellers managed to survive at all.