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10 creatures that thrive in caves

By: Bryan Nelson on Jan. 10, 2011, 1:08 p.m.
Mexican Tetra

Photo: Wiki Commons/GNU

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Mexican tetra

These fish are particularly fascinating because they come in two varieties. One variety is a normal-looking characin that swims in surface waters, and another variety is an eyeless albino that lives only in dark underwater caves.

Since these varieties can breed together, they are technically the same species, but it is nevertheless an animal on the verge of speciation — a change driven by the remote cave habitat where the blind variety dwells.