Rare Deep Sea Sighting of Enormous Phantom Jellyfish Leaves Scientists Puzzled

During a deep-sea mission off Argentina, scientists encountered a giant phantom jellyfish with a bell over three feet wide and arms stretching thirty-three feet, offering a rare glimpse of one of the ocean's most elusive creatures and deepening understanding of hidden marine ecosystems.

During a deep-sea exploration off Argentina, researchers recorded the presence of Stygiomedusa gigantea, a giant phantom jellyfish, at a depth approaching 3,000 feet. The specimen observed exhibited a bell wider than three feet and elongated ribbon-like arms reaching up to 33 feet. With fewer than 130 verified sightings in history, this encounter represents a rare opportunity to study one of the ocean's most elusive predators, primarily inhabiting the so-called midnight zone.

Unexpected Findings on a Research Expedition

The expedition, organized by the Schmidt Ocean Institute in January 2026, initially focused on investigating cold seeps—cracks on the seafloor releasing methane and hydrogen sulfide. These emissions sustain microbial communities that serve as the foundation of deep-sea ecosystems. While the team successfully located cold seeps, they also documented remarkable discoveries, including:

• The giant phantom jellyfish, Stygiomedusa gigantea
• Argentina’s first recorded deep-sea whale fall
• Twenty-eight potentially new marine species
• The largest known Bathelia candida coral reef, covering roughly 0.15 square miles

Research Focus: Cold Seeps and Deep-Sea Ecosystems

The primary aim of the expedition was to examine cold seeps, which support microbial life forming the base of the deep-ocean food web. Researchers employed remotely operated vehicles (ROVs), which allow safe exploration of extreme depths without human divers. These unmanned robots can collect data and record underwater life with exceptional detail. During cold seep exploration, the team unexpectedly encountered the giant phantom jellyfish, a rare event eliciting a combination of surprise and excitement from the scientists.

Characteristics of the Giant Phantom Jellyfish

Stygiomedusa gigantea ranks among the largest known jellyfish species. The observed specimen, approximately 820 feet off the Argentine coast, measured up to 33 feet in total length, with a bell exceeding three feet across. Sightings of this species remain extremely rare, with only about 120 recorded since its initial documentation in 1899. Preferring depths between 3,000 and 13,100 feet, these jellyfish remain largely hidden from human observation. Unlike typical jellyfish, Stygiomedusa gigantea lacks stinging tentacles and instead captures prey using its long, ribbon-like arms, primarily feeding on plankton and small fish. The specimen filmed was roughly comparable in size to a school bus, with the last recorded observation occurring in 2021 off California’s coast.

Additional Significant Discoveries

The expedition yielded further notable findings beyond the giant jellyfish:

• Argentina’s first deep-sea whale fall, located approximately 12,800 feet below the surface, providing a temporary ecosystem that sustains diverse marine species.
• The identification of 28 potential new species, including corals, worms, sea snails, sea urchins, and sea anemones.
• The largest known Bathelia candida coral reef, extending about 370 miles south of its previously recorded range, with an area comparable to that of Vatican City.

Scientific Outcomes and Biodiversity Insights

The research team documented an active cold seep covering nearly half a square mile, highlighting the ecological richness of Argentina’s deep-sea environment. Observations revealed a highly interconnected ecosystem with abundant marine life. Scientists emphasized that the expedition provided a detailed view of deep-sea biodiversity while underscoring the many remaining unknowns in these remote environments. The mission demonstrates the potential for unexpected discoveries and the critical role of advanced technology in deep-sea research. From the giant phantom jellyfish to newly identified species and whale falls, the expedition has expanded understanding of life in some of the planet’s most inaccessible aquatic habitats.

Sources:

• A Mysterious Giant Phantom Jellyfish Appears in Rare Deep Sea Encounter - A‑Z Animals
• Giant phantom jellyfish filmed in Argentina's deep sea (Press Office Ministry)
• Rare deep-sea jellyfish spotted in Argentina - Oceanographic Magazine
• Rare Giant Phantom Jellyfish Spotted Off Argentina During Deep-Sea Expedition - People.com
• Video. Giant phantom jellyfish spotted in Argentina's deep sea - Euronews
• A Mysterious Giant Phantom Jellyfish Appears in Rare Deep Sea Encounter