Scientists capture elusive deep-sea phantom jelly with 33-foot arms on camera

Rare Glimpse of Giant Phantom Jelly (Image: MBARI (Monterey Bay Aquarium Research Institute) / YouTube)

The ocean has always been a place of mystery and wonder. To many, it's the last real frontier on our planet. In spite of covering 71% of the Earth, humans have only explored about 20% of it. What lies beneath is still largely a mystery, but every now and then something amazing swims into view — such as the giant phantom jelly.

An Enigmatic Deep-Sea Resident

The colossal phantom jelly, or Stygiomedusa gigantea, was seen for the first time in 1899. When scientists collected a specimen at the time, they did not know they had one of a new species. Sixty years later, they finally realised its identity. To date, only about 100 times have they been seen. Such jellyfish inhabit the midnight zone, a dark sea layer well out of reach of humans.

Unlike most jellyfish, they don't sting prey. They sail instead with long, ribbon-like arms. These arms trap small fish and floating plankton. Their bell is over three feet wide. Tentacles reach up to 33 feet in length. Although not as huge as lion's mane jellies, they're still downright enormous.

The jellyfish has also appeared in oceans across the globe, with the exception of the Arctic. In 2025, it showed up in the frigid Bellingshausen Sea. It was photographed by an ROV — a remote-controlled robot from the surface. These cars make deep dives where humans are not welcome. Scientists observed as the jelly glided peacefully through pitch-dark waters.

New Technology, New Discoveries

The video was shot by the Monterey Bay Aquarium Research Institute, or MBARI. Their remotely operated vehicle got as deep as 3,200 feet below Monterey Bay, California. MBARI has only observed this jelly nine times despite making thousands of dives. Trawl nets were previously used to research deep-sea organisms, but jellyfish frequently disintegrated in them. Currently, 4K and high-definition videos allow scientists to observe fragile organisms alive.

This new footage reveals fine details of the jelly’s behaviour. It shows how the jelly moves and hunts in the dark. Scientists believe their diet includes plankton and small fish. While most jellyfish release eggs and sperm into the water, little is known about how phantom jellies reproduce. They may use a different method, but this remains a mystery.

A Hidden Shelter in the Deep

To my surprise, a few fish live within the arms of the jelly. A brotula, a very small fish, was observed doing this. It swims in and out of the jelly's arms, perhaps escaping predators. It receives parasites in return from the jelly's body. This peaceful cooperation serves both in an ocean that has no hiding spots.

Scientists also discovered other animals around the jelly in 2025. They were giant sea spiders and mysterious icefish. They even captured the first video of a glass squid. Every ROV dive teaches us more about what exists deep down below. The ocean is dark, but through technology, it is finally revealing its secrets.