Stygiomedusa gigantea is a very rare giant jellyfish, it lives in the depths of the sea: from 900 to 1800 meters. It has only been sighted about a hundred times. Its tentacles are not stinging but, generally, it uses them to move and to set traps for its preys.
Its diameter is 50–100 cm and its tentacles can reach 10 meters in length. As reported in a Nationa Geographic article, there are fewer than 130 sightings of this mysterious creature of the deep. The specimen, more than 9 meters long, was photographed for the first time off the coast of the Antarctic continent.
One sighting occurred several meters deep off the coast of Rongé Island, Antarctica. Upon their return to the surface, the tourists on the Viking Expeditions expedition vessel showed the images they had taken to Daniel M.
Moore, a marine biologist at the University of Exeter in the UK, and it was immediately clear that what they had seen was something incredibly rare. Up to that point there had been only 126 sightings since it was first described in 1910, including specimens caught in nets and footage recorded from remotely operated underwater vehicles.
Even scientists at the Monterey Bay Aquarium Research Institute, who have made thousands of hours of submersible diving, only sighted nine. This jellyfish has been repeatedly observed accompanied by a small fish that lives next to it.
This is a mutually beneficial relationship, as the fish receives shelter and protection from the jellyfish, which in return protects against disease by feeding on parasites that may attach to its body. We still know very little about this rare and enigmatic jellyfish.
In particular, its mode of feeding is still unknown, as it does not have stinging filaments. This jellyfish has incubation pouches, suggesting a viviparous mode of reproduction. The giant ghost jellyfish has a rounded, bell-shaped umbrella that can reach 1.40 m in width.
It also has four long draped-looking mouth arms which can reach 10 meters in length and which, having no stinging tentacles, seem to be used to trap its prey, which probably consists of plankton and small fish. Its color is a dark red that evolves towards black6.
This jellyfish appears to be one of the largest invertebrate predators in the deep sea ecosystem. Its grim appearance and gigantic size have earned it a terrifying scientific name.