PLANET EARTH Caves

This isolation has resulted in the evolution of some various strange creatures. They are the cave specialists - troglodytes（类人猿，同时有隐居者的意思）, animals that never emerge from the caves or see daylight. These troglodytes from Thailand are possibly the most specialized creatures on Earth for they live only in cave waterfalls. The entire population of these cave angel fish seems to be restricted to just two small caves.



It's the same story with other troglodytes. There may well be less than a hundred Texas（德克萨斯） cave salamanders in the wild. And the Belizean（伯利兹） white crab is another creature that is unique to just one cave system. Living in perpetual（永久的） darkness they have all not only lost the pigment in their skin, but also their eyes. It takes thousands of generations for eyes to be lost, so these species must have been isolated for a very long time.



But the blind salamander has other highly developed sensory organs. Receptors in their skin detect minute movements in the water made by its prey. External gills（腮） help it to breathe in water that is particularly low in oxygen. The cave angel fish feed on bacteria in the fast flowing water keeping their grip with microscopic hooks on their fins. Food is often in short supply and troglodytes like the crab have to survive on whatever washes into the cave from outside.