Black dragonfish (Idiacanthus atlanticus) swim in the subtropical and temperate waters of the Southern Hemisphere, traveling as deep as 2,000 meters (6,562 feet) below the surface of the sea.

The unusual species are sexually dimorphic, meaning the males and females look remarkably different from each other. The females have barbels on their chin, fang-like teeth and can grow up to 40 centimeters in length. 

Males, on the other hand, have no chin barbels, lack teeth and are just five centimeters long. They also lack a functional gut, which means they never eat, and only live long enough to mate.  

Researchers believe the gender difference is an evolutionary method to reduce competition for resources while still retaining the ability to mix their genes through sexual reproduction. 

As with many deep sea creatures, these bioluminescent fish have photophores that can produce light. Researchers believe the luminous tip on the barbel acts like a fishing lure, wagging languidly through the water while flickering on and off to attract the attention of their prey.

The larvae of the black dragonfish also have their own set of unusual traits. The larvae are transparent with eyes at the tip of long stalks that are half their body in length. As they mature, the stalks shorten until they become absorbed into the sockets of the skull. It is also during this time that they change into either the ink-black color of womanhood or the dark brown color of manhood.