The
tiny sea sapphire has hexagonal guanine crystals embedded in the
segments of its shell. They reflect the surrounding light in splashes of
vibrant color. But you can enjoy its beauty for only a moment. When it
reflects light right back at you, the sea sapphire vanishes from sight.
The
New Scientist describes how this little creature hides:
In
blue sea sapphires, the distance between the crystals is about the same
as the wavelength of blue light, so the animals appear blue.
The
angle of light hitting the sea sapphire also affects the color and lets
it perform its disappearing act. For the species in the video, for
example, the animal’s tilt of 45 degrees causes the reflected light to
slip into the ultraviolet spectrum, and the animal becomes invisible to
our eyes.
Only male sea sapphires have such coloration, which they probably use to attract mates, just like how human males use fedoras.
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