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Colour-shifting sea sapphires are some of the world's most mesmerising and most elusive creatures.

These miniature crustaceans are capable of shimmering their way through the whole colour spectrum before disappearing altogether. Just like with peacocks, it is only the males of the species that are capable of these iridescent displays. And now, for the first time, researchers have figured out exactly how they do it.


Each sapphire's skin is packed with alternating layers of hexagonal crystals that are arranged like honeycomb, and these layers are filled with cytoplasm. Researchers from the Weizmann Institute of Science measured the reflections that came off both the cytoplasm and the crystals themselves before realising that the changes in the depth of cytoplasm corresponded with the changes in hue. Whereas the stacks of crystal were consistently 70 nanometers thick, the depth of cytoplasm varied wildly measuring between 50 and 200 nanometers.

They also found that the colour of the sapphire strongly depended on the angle of orientation relative to the light source, and this is what it allows it 'disappear'. When lights hit the crustacean at an angle of 45 degrees, it shifts out of the visible range into the ultraviolet range, which renders it invisible to the naked eye.

The discovery will likely impact ideas for the practical harnessing of biomimicry techniques; due to the clever reflective mechanism that allows the critters to disappear completely, it could even (stop us if you've heard this before) one day led to the creation of 'invisibility cloaks'... Maybe.

Details of the discovery have been detailed in the American Chemical Society, which has also published a video describing the sea sapphires as "the most beautiful animal you've never seen". Check out the video to watch them disappear and reappear in the blink of an eye.