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