This species presents one of the most extreme cases of sexual dimorphism known. The female is up to 40cm long, with small eyes, chin barbel, and long fang-like teeth, which are used for catching its primary food item - other fish.
By contrast, the male is just 5cm, has no teeth, no chin barbel, a non-functional gut, and is dark brown rather than black.
Perhaps most extraordinary is larval development - the eyes of the larvae are carried on long stalks that retreat as the fish reaches maturity and the eyes are nested in sockets.
Makes a light you cannot see to hunt its prey
Like many deep sea fish, the black dragonfish can produce its own light.
It is covered with photophores along lower and upper surfaces, and has photophores under its eyes and at the end of its long barbel. When disturbed it lights up all over, even down the lengths of its fins.
However, unlike almost all the other bioluminescent organisms in the ocean, it can glow and perceive a red as well as blue-green light.
The light of the black dragonfish can be such long wavelengths that it is almost infrared and barely visible to the human eye. The ability to produce this type of light gives the black dragonfish an enormous advantage over its prey as it can find its way to unsuspecting prey through the deep dark depths of the ocean.