The cheek lights on the deep-sea Loosejaw Stoplight Fish(Malacosteus sp.) may serve to locate prey in the dark, but they likely also function in mate selection, since the organs of males are much larger than those of females. When not in use, these lights can be rotated and pulled back into the fish’s head, sort of like the headlights on some cars. They also can be flashed on and off. So why retract them? Probably because they have a highly reflective layer that helps direct light outward.
