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11 intriguing transparent animals

By: Bryan Nelson on Jan. 24, 2011, 11 a.m.
Crocodile icefish have transparent blood.

Photo: uwe kils/Wikimedia Commons

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Crocodile icefish

These ghostly Antarctic predators are unusual because their transparent appearance is due in large part to nearly invisible blood. They are the only known vertebrates in the world without hemoglobin, the protein in blood that transports oxygen.

They survive without hemoglobin thanks to the subzero temperatures of the ocean where they live, since cold water has a much higher dissolved oxygen content than warmer water. They also have a larger heart and produce antifreeze glycoproteins, which lowers their internal body temperature so they can survive in the deep ocean.