A thousand feet below the waves, tiny ocean crustaceans known as sea sapphires dance about like microscopic disco balls. But at the water’s surface, where they feed, these copepods are all but invisible.
Their signature dazzle is derived from tightly packed crystals that lie just below the animals’ outermost shell. Made of a chemical compound called guanine, a main component of DNA, these crystals are arranged in a regularly alternating pattern of hexagons that reflect light, according to a 2015 study.
“The colors are apparently used by the copepods for signaling and communication,” says study leader Lia Addadi, a structural biologist at the Weizmann Institute of Science in Israel. (See amazing pictures of animals that glow.)
Only male sea sapphires have the crystals necessary to reflect light in the blue and purple wavelengths. The females are transparent, though their eyes can likely detect the male copepods and their shiny gyrations, Addadi says.
Of course, sea sapphires are far from the only creatures in the sea that get their glam on.
Hawksbill Sea Turtle
Don’t worry, this glowing sea turtle—filmed in 2015 by National Geographic Emerging Explorer David Gruber—is not radioactive.
Instead, Gruber says the critically endangered hawksbill sea turtle displays a new form of biofluorescence, something that’s common in coral, jellies, and fish, but never before seen in sea turtles. (Related: "Move Over, Glowing Turtle—Meet the Glowing Eels.")
Unlike bioluminescence, in which an animal creates its own light, biofluorescent creatures absorb light at one wavelength and then emit it at another.
Depending on which angle you look at it, the sea mouse resembles either a dust bunny or an iridescent toupee.
That's because these bottom-dwelling creatures, which are actually polychaete worms, make use of structural color in a similar fashion to the sea sapphire.
However, instead of guanine crystals, the worms produce long spines of protein that are capable of reflecting 100 percent of the wavelengths of light perceptible to the human eye. Scientists suspect the sea mouse’s shimmery spines may be used for communication, courtship, or defense.
Anglerfish are notorious for attracting prey with their bioluminescent lures, but what if those prey also possessed chemical weapons?
One shrimp species, Acanthephyra purpurea, takes on predators by hocking a cloud of ice-blue bioluminescence into the face of anything that gets too close.
While there’s little information about these animals in the scientific literature, Steven Haddock at the Monterey Bay Aquarium Research Institute believes the shrimp create their own weaponry, instead of borrowing it from other life-forms.
Talk about tangled up in blue—each April, Japan’s shores shine electric blue thanks to millions of firefly squid bubbling from the ocean depths. (See "Large, 'Glamorous' New Glowing Squid Species Found.")
Why have they come? And why do they glow?
No one knows, but considering that the firefly squid is thought to be the only squid capable of color vision, it seems to be some sort of communication.
If you ever come across a translucent tube the size of a whale, fear not—these blobs have no intention of devouring you.
In fact, these giants, called pyrosomes, are actually made up of thousands of much smaller creatures called zooids. Not only are the zooids clones of one another, but they’re connected by shared tissues.
As the colony grows in size, they form an enormous structure that coasts through the ocean by squirting water out of its open end, a bit like an octopus.
It’s thought that the zooids flash their own light organs in response to disturbances, which then trigger light reactions from the rest of the colony.
Not every animal has the luxury of total illumination like the pyrosome. So what’s a little gastropod to do?
If you’re the clusterwink snail, you use magic crystals to give your bioluminescence a boost. According to Dimitri Deheyn, a marine biologist at the Scripps Institution of Oceanography, the snail’s shell contains carbonate minerals called aragonite that amplify light thousands of times.
Intriguingly, aragonite crystals only showcase the wavelength of light produced by the snail, which is bluish green. How’s that for anti-counterfeiting?