Creatures that dwell hundreds of meters below the ocean’s surface are notoriously strange and alluring, and the lanternshark is no exception. Mysterious fluorescent markings, called lateral photophores, flank both sides of the small, slender shark’s body, glowing vibrantly in waters that are otherwise black (pictured). Deep-sea researchers have struggled to understand why these markings exist; they don’t lure prey, they’re certainly not helpful for camouflage, and they don’t warn predators to stay away. So what are they for? Finding a mate, according to a new study. The flashy markings help facilitate intraspecific communication, or communication within the same species, researchers report online today in Royal Society Open Science. It can’t be easy attracting a partner in the dark; males and females glow from different parts of their bodies and scientists think that this helps them locate a mate. Whatever the reason, the glowing marks have been an evolutionary success story; about 40 species of lanternsharks now sport them.