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The Strange World of Troglobites | 20 Years of Planet Earth | BBC Earth - Video học tiếng Anh

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

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0:00It takes thousands of generations for

0:02eyes to be lost. So these species must

0:05have been isolated for a very long time.

0:09Many caves are like islands cut off from

0:12the outside world and from other caves.

0:23This isolation has resulted in the

0:26evolution of some very strange

0:29creatures.

0:32They are the cave specialists,

0:34troglobites, animals that never emerge

0:37from the caves or see daylight.

0:53These trogloites from Thailand are

0:56possibly the most specialized creatures

0:58on Earth, for they live only in cave

1:01waterfalls.

1:03The entire population of these cave

1:06angelf fish seems to be restricted to

1:09just two small caves.

1:15It's the same story with other trogler

1:17bites. There may well be less than 100

1:19Texas cave salamanders in the wild.

1:39And the Blelesian white crab is another

1:42creature that is unique to just one cave

1:45system.

1:51Living in perpetual darkness, they have

1:53all not only lost the pigment in their

1:55skin, but also their eyes.

2:00It takes thousands of generations for

2:02eyes to be lost. So these species must

2:05have been isolated for a very long time.

2:13But the blind salamander has other

2:16highly developed sensory organs.

2:21Receptors in the skin detect minute

2:24movements in the water made by its prey.

2:33External gills help it to breathe in

2:36water that is particularly low in

2:38oxygen.

2:50The cave angelf fish feed on bacteria in

2:54the fast flowing water, keeping their

2:56grip with microscopic hooks on their

2:58fins.

3:10Food is often in short supply and

3:13trogabites like the crab have to survive

3:16on whatever washes into the cave from

3:18outside.

3:23A salamander might not encounter food

3:25for several months, so when something

3:28does come along, it can't afford to miss

3:30it.

3:38It's astonishing that these

3:39extraordinary cave dwellers managed to

3:42survive at all.