The ghostly giant is an extremely rare sight and now we have excellent footage to help us learn about it.
Out of the darkness of the ocean’s midnight zone, a remotely operated vehicle (ROV) of the Monterey Bay Aquarium Research Institute (MBARI) spots a billowing crimson curtain. When the submersible moves in for a closer look, its lights reveal the outline of a giant jellyfish (Stygiomedusa gigantea).
Known in English as the “giant phantom jelly,” every sighting of this mysterious animal is a celebration for ocean researchers. It was first collected in 1899, but since then scientists have only encountered this animal about 100 times, even though we’re talking about a large animal that appears to have a worldwide distribution. So why the few sightings? Well, accessing these animals’ deep-water habitat has posed a great challenge.
This is where MBARI’s remotely operated devices come into the picture. Such vehicles have meant a great leap forward in learning about deep-sea life and MBARI’s ROV Doc Ricketts has now further added to our knowledge by providing the amazing footage below. The ROV spotted this giant phantom jelly in November 2021, at a depth of 990 meters (3,200 feet) in Monterey Bay. This deep-sea denizen has a bell that measures more than one meter (3.3 feet) across and trails four ribbon-like oral (or mouth) arms that can grow more than 10 meters (33 feet) in length.
Even today, we know very little about the giant phantom jelly. Historically, scientists relied on trawl nets to study deep-sea animals, and while such nets can be effective for studying hardy animals such as squids, crustaceans, or fish, jellies turn into a gelatinous goo in them. The cameras on MBARI’s ROVs, on the other hand, have allowed researchers to study these animals intact in their natural environment. High-definition footage of the giant phantom jelly capture stunning details about the animal’s appearance and behaviors that scientists would not have been able to see with a trawl-caught specimen.
MBARI’s observations of the giant phantom jelly have helped illuminate the animal’s ecological role in the ocean’s depths. During an expedition to the Gulf of California, for example, another MBARI ROV, Tiburon, recorded a fish -the pelagic brotula (Thalassobathia pelagica) – alongside a giant phantom jelly. Researchers watched as the brotula hovered above the bell of its host and swam in and out of the jelly’s enormous oral arms. As the wide-open depths of the midnight zone offer little shelter, many creatures find refuge in the gelatinous animals that are abundant in this environment.
Here are some more amazing photos and facts about the giant phantom jelly from MBARI:
The giant phantom jelly (Stygiomedusa gigantea) has an unusual appearance and remarkable size, and it also exhibits a unique life history. Most jellies alternate between a swimming stage (called a medusa) and an attached stage (called a polyp or hydroid). But female giant phantom jellies brood their young in pouches beneath that broad bell and give birth to their young live. Image: © 2007 MBARI
Encountering the giant phantom jelly is a rare treat, even for MBARI researchers. In over 34 years of deep-sea research, they have only observed this species nine times. This individual was spotted with the ROV Doc Ricketts at a depth of 990 meters (3,200 feet) in Monterey Bay. Image: © 2021 MBARI
The giant phantom jelly has a reddish coloration, similarly to many other deep-sea animals. Since red light cannot penetrate to the ocean’s depths, animals that are red appear black and camouflaged in the darkness. Scientists are unsure what animals might prey on the giant phantom jelly, but its crimson color and large size likely help deter most predators. Image: © 2018 MBARI
The giant phantom jelly was first collected in 1899. Since then, scientists have only encountered this animal about 100 times. It appears to have a worldwide distribution and has been recorded in all ocean basins except for the Arctic. The challenges of accessing its deep-water habitat contribute to the relative scarcity of sightings for such a large and broadly distributed species. MBARI’s ROV Tiburon observed this individual in the outer reaches of the Monterey Canyon at a depth of approximately 1,100 meters (3,600 feet). Image: © 2007 MBARI 
MBARI’s ROV Tiburon recorded this giant phantom jelly while drifting in the currents just above the deep seafloor during an expedition to the Channel Islands off the coast of Southern California. Image: © 2005 MBARI
The giant phantom jelly does not have tentacles. Instead, it uses four blanket-like oral (or mouth) arms lined with stinging cells to stun prey. We don’t know what the giant phantom jelly eats, but scientists suspect it dines on plankton and perhaps small fish. Image: © 2007 MBARI 
Most observations of the giant phantom jelly have occurred in deep water. MBARI has recorded this species at depths of 750 to 2,200 meters (2,500 to 7,200 feet) in Monterey Bay, the Juan de Fuca Ridge, and the Gulf of California. In the cold waters around Antarctica, the species has been seen in shallow waters. Image: © 2021 MBARI
Sources: 1, 2, 3, 4
