The first giant phantom jelly specimen was collected in 1899 and described in 1910. The species has only been spotted around 120 times since. This is because these jellies generally live in deep waters, down as far as 22,000 feet (6,700 m) below the surface.

They have compressible, squashable bodies, which help them to survive the incredibly high pressures they experience at these depths.

Giant phantom jellies also differ from other jellyfish by being viviparous, meaning they give birth to live young. The young develop inside the mother before detaching from inside the hood and swimming out of their mother’s mouth.

Unlike other jellyfish, giant phantom jellies don’t have stinging tentacles to catch prey. Instead, they wrap their arms around their food — usually plankton or small fish — and hoist them into their mouths.

These jellyfish are solo explorers, but they also appear to help to protect smaller sea creatures. During an expedition in the Gulf of California, researchers from the Monterey Bay Aquarium Research Institute spotted small fish, pelagic brotula (Thalassobathia pelagica) sheltering underneath a giant phantom jelly. In return, the fish aided the jelly by removing parasites.