A tiny species of copepod is one of the most hypnotizing sea creatures you may ever see. About the size of an ant, male sea sapphires can flash iridescent colors when the light hits their bodies just right, and in a flash turn so transparent that they're practically invisible.
Their ability to blaze in bright colors comes from layers of crystal plates on the skin cells of the creature's back. Different species have different layers of plates, and thus different species flash different colors from red to gold to blue. It is unknown exactly why the males are able to shine like this, though researchers speculate that it could be to draw the attention of females or to compete with other males, or it could be a way to avoid predators. But what has been discovered is how the colorful optical trick is pulled off.
According to Science Magazine, "[R]esearchers have measured the light reflectance of several different-colored male species and compared the thickness of their crystal plate layers with the cytoplasm nested in between. They found that changes in the thickness of the cytoplasm layers, not the crystal layers, determined what color was reflected ... And for one species, they discovered that light hitting the crustacean at a 45° angle caused the reflectance to shift out of the visible range into the ultraviolet, rendering the animal almost invisible."
Here is a video of a sea sapphire flashing back and forth from brilliant blue to completely invisible as it twists in the water:
The creatures are truly spectacular and create quite a sight for those lucky enough to spot them in the sea. Deep Sea News writes, "When they’re abundant near the water’s surface the sea shimmers like diamonds falling from the sky. Japanese fisherman of old had a name for this kind of water, 'tama-mizu', jeweled water."