This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Many animals go to great lengths to attract a mate. This goal is especially challenging for a solitary animal, such as the octopus, living in the large, lonely ocean. Another major disadvantage: being a deep-sea octopod that lives in the dark, vast water column.
But the females of Bolitaena pygmaea have a peculiar—and apparently effective—strategy: A glowing ring around their mouths. This bioluminescent ring appears only on the ladies of this small, gelatinous species—and only when they are mature and ready to mate.
The light-producing organ gives off a yellowish glow, which must be quite a sight for potential mates in the deep-ocean dark. But scientists speculate that the mating game for B. pygmaea is more complex than simply searching for a stranger somewhere in the night. The presence of males seems first to draw females to the area. This might be accomplished by chemical signals released from the males' extra-large salivary glands. Only once the females are in the general vicinity do they seem to draw in the males by flashing their alluring beacon.
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Keeping this bright light dark most of the time might also be a wise survival strategy—and not just to avoid unwanted suitors. A constant glow could risk catching the attention of predators. And with total mantle lengths less than five centimeters, these tiny octopuses have many (bigger) hungry animals to hide from. Although the unusual yellow wavelength her photophore emits might also help avoid detection by other animals.
These females' glow is second only to the most bioluminescent octopus, the aptly named glowing sucker octopus (Stauroteuthis syrtensis), which comes from a different family of octopuses altogether.
Once the females have attracted their mate, sealed the deal and are ready to lay their eggs, they find a safe spot to hang out, some 800 meters below sea level. There, the light is so faint that they are unlikely to be spotted by a potential predator. They carry their eggs in their suckers close to their mouths for several months before the offspring are ready to emerge. After hatching, these young live closer to the surface—about 200 meters below—until they start descending to greater depths as they get grow (relatively) larger (from their hatchling size of just a few millimeters).
Lacking the flashy flesh, the males are rarely spotted by human observers. And mature males have hardly ever been seen. Mature females and almost-mature males have been documented some 1,200 to 1,400 meters below the surface.
These illuminated mouths aren't the only odd thing about this strange species of octopus. Both the males and females have eyes that are raised on long stalks. All the better to see you with—glow or no-glow.
Illustration courtesy of Ivan Phillipsen