.One thousand meters under the sea, where the red wavelength of sunlight doesn't penetrate, red organisms are effectively invisible. But things are trickier in the middle ocean depths, between 600 and 1000 meters, where sunlight can still reveal the silhouettes of colorful sea creatures. So a couple of mid-ocean-dwelling cephalopods—the animal class including octopuses and squids—have come up with a flexible strategy: Start out transparent, but change colors whencertain predators come aro...
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