Sea Sapphire's 'Magic Trick' Of Sudden Invisibility Discovered

By R. Siva Kumar - 03 Sep '15 08:52AM

There is a hidden lever that controls the "magic trick" of tiny ocean creatures called sea sapphires.

The trick is to be all there for a while---and then not. Sometimes they look brilliant with shades of blue, purple or green, after which they go invisible, says the Weizmann Institute of Science. The "trick" helps them to avert a predator's hungry gaze, even while they struggle to attract mates.

Sapphirinidae are part of a subclass of crustaceans called copepods. Being almost microscopic, they are mostly tough to examine.

Scientiests studied the crystal layers on the backs of male Sapphirinidae from various species, measuring the reflectance to determine color, and also using a microscope technique to probe into the crystal organization.

They found that the colors are caused by light that reflects off a multilayer reflector. It is called a photonic crystal, and is made up of crystals of guanine.

"The researchers observed that the guanine plates in Sapphirinidae are stacked in precise periodic arrays and the spacing between these plates determines the creature's color. When males of certain Sapphirinidae species rotate their backs to the light at a 45-degree angle as they perform a spinning maneuver, the wavelength of the reflected light is shifted out of the visible light range, leaving them invisible. The researchers determined the spacing between the plates acts as a sort of wavelength "tuning" mechanism that determines the Sapphirinidae's color. The closer the plates are to one another, the shorter the wavelength and the bluer the reflected light," according to hngn.

This is a new discovery that could help to examine the world of Sapphirinidae and also make designs for "artificial photonic crystal structures" managing the flow of photons. Such devices can be used for applications such as "adaptive or changeable reflective coatings, optical mirrors and optical displays."

The findings were published in a recent edition of the Journal of the American Chemical Society.