A giant jellyfish approximately 11 meters long amazed Argentine scientists during an expedition in the depths of the Argentine Sea.
In particular, it is a specimen of Stygiomedusa gigantea, known as the phantom jellyfish, which was recorded on video at a depth of 253 meters.
The discovery occurred during the “Life in Extremes” expedition, led by researchers from the National Council of Scientific and Technical Research (CONICET) and the University of Buenos Aires.
The campaign took place between December 14, 2025, and January 10, 2026, aboard the research vessel R/V Falkor (too).
The scientists traveled from the port of Buenos Aires to Tierra del Fuego.
There, they explored poorly documented regions such as the Colorado-Rawson submarine canyon and the largest known reef of Bathelia candida.
What the giant jellyfish is like
The documented specimen measures “as much as a school bus,” according to the researchers in an official statement.
This giant jellyfish is distinguished by its unique characteristics in the deep ocean.
The species has four oral arms that can reach up to 10 meters in length.
Unlike other jellyfish, it lacks stinging tentacles. Therefore, this giant specimen is relatively harmless, as it uses these arms, resembling large sheets, to trap plankton and small fish.
The jellyfish’s bell can reach nearly one meter in diameter. This structure intensifies the visual impact of the marine discovery.
A rarely documented species
Since its first scientific record in 1910, the Stygiomedusa gigantea has only been documented about 130 times worldwide.
Thus, this new discovery of the giant jellyfish highlights the importance of the Argentine Sea as a refuge for little-known species.
María Emilia Bravo, chief scientist of the expedition, emphasized the value of the discovery.
According to her, the team was surprised “by the diversity detected in the depths,” according to the official statement.
In this way, the record of the Argentine continental slope helps to highlight the richness of national marine biodiversity.
For the researchers, observing such enigmatic species reinforces the importance of continuing explorations in the Argentine deep ocean.
The technology used by CONICET for the new expedition
The team used the remotely operated vehicle (ROV) SuBastian to document the giant jellyfish. This advanced tool descends to 4,500 meters deep.
The ROV allowed for obtaining high-definition images without altering the ecosystem. This represented a significant improvement over old trawl nets, which damaged the captured species.
The campaign also recorded, for the first time in national waters, a whale fall at 3890 meters deep.
This phenomenon creates temporary ecosystems and provides food for species such as octopuses, sharks, and crabs.
Additionally, the group explored the largest known reef of Bathelia candida. There they reported a varied and previously unknown community of species.
The experience aboard the R/V Falkor (too), with this giant jellyfish at the forefront, highlighted the hidden biological richness in the Argentine Sea.
Moreover, it leaves open the question about the magnitude of the life yet to be discovered beneath its waters.
