Stygiomedusa gigantea, commonly known as the giant phantom jelly, is the only species in the monotypic genus of deep sea jellyfish, Stygiomedusa. It is in the Ulmaridae family.[2] With only around 110 sightings in 110 years, it is a jellyfish that is rarely seen, but believed to be widespread throughout the world, with the exception of the Arctic Ocean.[3][4][5]
The Monterey Bay Aquarium Research Institute's remotely operated underwater vehicles have only sighted the jelly 27 times in 27 years. A study conducted by the Journal of the Marine Biological Association of the United Kingdom, focusing on four Stygiomedusa gigantea present in the Gulf of Mexico, revealed information regarding the wider distribution of this species. S. gigantea is thought to be one of the largest invertebrate predators in the ecosystem.[3] It is commonly found in the ocean's midnight zone, reaching depths as deep as 6,665 m (21,867 ft).[5]
S. gigantea has an umbrella-shaped bell that can grow up to 1 m (3.3 ft).[6] The bell's pliant tissue allows for the jellyfish to stretch 4 to 5 times its size, presumably to engulf their prey. Their four arms have a "paddle-like" or "kite-like" shape and can grow up to 10 m (33 ft) in length. The arms grow in a "V" shape transversely,[7] with a wider base and tapering towards the ends. They do not have any stinging tentacles and instead use their arms to trap and engulf their prey which consists of plankton and small fish.[5][3] From Browne's analysis of a collected S. gigantea, their jelly appears a red-orange color only when there is visible light.[7] However, since they dwell in the deep ocean, visible light does not penetrate far enough. Thus, the giant jellyfish may appear "invisible" or glow orange very faintly in its surroundings, depending on the depth of the water. Furthermore, their bodies being made of either spongy tissue or jelly allows for the species to withstand the enormous deep ocean pressure of 40,000 kPa (5,800 pounds per square inch). The circular stomach contained canals that travel to the surface of the sub-umbrella. It is inferred that the lower stomach is thick to ensure the species has the strength to carry their long arms. Its four genital openings were also small to avoid weakening the stomach.[7] Since there were no gastric pouches nor radial canals, the jellyfish was determined to be a part of the Ulmaridae family.[citation needed]
Sightings of Giant Phantom Jellyfish in the Antarctic Ocean. Although the Stygiomedusa is not native to the arctic ocean there have been sightings of the jellyfish in the Antarctic Ocean, with the help of submersibles.
Daniel M. Moore, a marine biologist with Exeter University in the U.K. and chief scientist for Viking Cruises states that the reason Antarctic waters below 160 feet haven’t yet been well explored is that they are so difficult and expensive to reach. However, the frequent encounters with this animal are that tourism expeditions in the Antarctic are increasingly offering personal submersibles to guests to take photos. This leads to the sighting of the Giant Phantom Jellyfish hundreds of feet underwater off the coast of Antarctica’s Rongé Island. The Viking Expeditions cruise ship had shown those photos taken with the private submersibles to Daniel M. Moore.
The observations of the rarely encountered Stygiomedusa gigantea at depths of 80–280 m (the mesopelagic and lower epipelagic zones) around the Antarctic Peninsula coastal waters. The Norwegian Polar Institute, an international peer-revied journal called Polar Research, which corresponds to Daniel M. Moore of Viking Expeditions, found the Stygiomedusa Gigantea in the Antarctic Peninsula at Georges Point, Rongé Island, Fournier Bay, Anvers Island, and Paradise Harbour.