Researchers Capture Footage of Deep-Sea Giant Phantom Jelly With 33-Foot Arms

Earth’s oceans cover 71% of the planet, but humans have only explored less than 20% of the seas. Scientists believe there are many undiscovered creatures living in its depths. Some species, like the elusive giant phantom jelly, are known to exist, but we still have a lot to learn about these ocean giants. Some of the best information we have on giant phantom jellies has only been discovered recently, when scientists operated remotely operated underwater vehicles (ROVs) to capture footage of the jelly swimming in its habitat, as shown in this YouTube video posted by MBARI (Monterey Bay Aquarium Research Institute).

What Is a Giant Phantom Jelly?

The giant phantom jelly (Stygiomedusa gigantea) is a deep-sea jellyfish that was first discovered in 1899. At the time, scientists collected a specimen. However, they didn’t realize it was a newly discovered species of jellyfish until 60 years later. There are around 200 species of jellyfish in the world’s oceans. Most of them range from tiny to a few feet long. There are a few jelly species, however, that reach enormous sizes. The lion’s mane jellyfish, for example, can grow tentacles as long as 60 feet.

Although they don’t grow as large as the lion’s mane jelly, giant phantom jellies can be massive, reaching over three feet across with 33-foot-long tentacles. They live in the midnight zone of the ocean where it is constantly dark. Although we aren’t sure, scientists can infer that phantom jellies feast on a diet of small fish and plankton.

Not a lot is known about the giant phantom jelly. Even though a specimen of the creature was collected over 100 years ago, there are only about 100 reported sightings of scientists encountering the animal. The reason for our lack of knowledge is that giant phantom jellies live deep in the ocean and are not often seen by humans.

Where Do Phantom Jellies Live?

Giant phantom jellies can be found in every ocean except for the Arctic. However, you won’t see them on a typical dive. These mysterious creatures live at depths too far for humans to reach. In a YouTube video posted by MBARI (Monterey Bay Aquarium Research Institute), we can witness the massive jelly swimming peacefully in the dark ocean waters at a depth of 3,200 feet deep in Monterey Bay, off the coast of California.

The film was taken by an ROV. This is an unmanned underwater vehicle that can reach great depths while under the control of someone on the surface. According to MBARI, “MBARI’s ROVs have logged thousands of dives, yet we have only seen this spectacular species nine times.”

How Do Phantom Jellies Differ From Most Jellyfish?

Most jellyfish sting their prey, paralyzing the animal before they begin to eat. The giant phantom jelly is different, however, in that it doesn’t have stinging tentacles. Instead, phantom jellies have four ribbon-like arms that trail behind them as they swim. They use their arms to wrap up small fish and plankton and move them into their mouths.

Another way they differ is that the reproductive biology of the giant phantom jellyfish is not well understood. While most jellyfish release sperm and eggs directly into the water, scientists are still studying how phantom jellies reproduce, and there is currently no confirmed evidence that they give birth to live young.

Some Fish Find Refuge With the Phantom Jellies

There aren’t many places to hide in the ocean’s midnight zone. There are no coral reefs or plants to take shelter in. Scientists believe some small fish take shelter within the phantom jellyfish’s billowing arms. Researchers once spotted a small fish called a brotula swimming in and out of the jelly’s arms. While the fish took shelter, it also benefited the jelly by removing and eating parasites on its arms.

Scientists Are Learning More Than Ever Before About the Deep Sea With ROV Expeditions

In the past, scientists studying deep-sea creatures had to rely on catching specimens in trawl nets. Although this method works for hardy sea creatures such as crustaceans and fish, jellyfish tend to disintegrate in the nets. By using ROVs that can reach deep enough to find giant jellyfish and other deep-sea creatures swimming in their habitats, scientists are able to gain a much broader understanding of the animals.

According to MBARI, “High-definition — and now 4K — video of the giant phantom jelly captures stunning details about the animal’s appearance and behaviors that scientists would not have been able to see with a trawl-caught specimen.”

The most recent sighting was in 2025 when the giant phantom jellyfish was spotted by an ROV in the Bellingshausen Sea off Antarctica. In addition to the phantom jellyfish, researchers discovered giant sea spiders and icefish, and recorded the first-ever footage of a glacial glass squid.

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