The Seven-Armed Voice of the Deep: MBARI Captures Rare Haliphron atlanticus

In December 2025, the team at the Monterey Bay Aquarium Research Institute (MBARI) successfully recorded footage of one of the ocean's most elusive inhabitants: the octopus species Haliphron atlanticus, commonly known as the 'seven-arm octopus.' This significant sighting occurred approximately 700 meters beneath the surface in Monterey Bay, California, USA, captured using a remotely operated vehicle (ROV).

This moment was not a sensational anomaly breaking the norm of the ocean; rather, it was a fleeting glimpse into its standard operations. Yet, that brief second fundamentally shifted the perspective on what lies in the abyss.

Discovery Details

The moniker 'seven-arm' is not a reflection of a biological error or an anomaly. Like all other octopuses, Haliphron atlanticus possesses eight arms. The illusion of only seven arises from a unique feature in the males: the eighth arm, known as the hectocotylus, is specialized for transferring spermatophores and is frequently kept tucked away in a pouch beneath the eye. Consequently, observers often see only seven appendages, leading to the nickname that has become popular in descriptions of the species.

Several key facts solidify the importance of this observation:

• The recording was made by an ROV apparatus, complete with precise operational parameters, including the exact depth.
• The species was definitively identified as Haliphron atlanticus.
• This event adds to a rare statistical record: for MBARI, this marks only the fourth confirmed sighting of this particular octopus in the region across nearly four decades of operation.

MBARI, established in 1987, operates as a private, non-profit oceanographic center. The Institute is renowned for systematically developing the 'eyes of the ocean'—advanced underwater robotics, including its fleet of ROVs. Its campus in Moss Landing provides researchers direct access to one of the deepest underwater canyons along the continental coast of the United States. This unique geographical advantage has made Monterey Bay a premier window for humanity into the deep sea.

Understanding Haliphron atlanticus

Haliphron atlanticus thrives in the mesopelagic and bathypelagic zones, typically encountered at depths ranging from about 200 to 900 meters. This species exhibits pronounced sexual dimorphism: females can grow to considerable sizes, with reports noting measurements reaching tens of kilograms and several meters in length, while males are noticeably smaller. The life cycle for many octopuses is often dramatic; males frequently perish after mating, and females typically die after releasing their eggs.

Previous research suggests that the diet of Haliphron atlanticus often includes gelatinous organisms, such as jellyfish. This dietary detail is crucial as it grounds the octopus firmly within deep-sea ecology, confirming its role within the intricate abyssal food webs rather than remaining a mere myth.

For the scientific community, an encounter like this is far more valuable than just obtaining a rare piece of footage. It provides essential material for ongoing analysis, including:

• Refining our understanding of the species' behavior and its precise position within the food chain.
• Gaining deeper insight into the structure of deep-sea ecosystems and how they are responding to environmental changes.

What does this event add to our global narrative? It underscores the subtle, foundational truth of the deep: life persists even where we have yet to learn how to look without haste. It reinforces the certainty that the ocean's story is far from fully told. As it begins to reveal its pages, every new life form encountered sounds like a fresh letter added to the Earth's alphabet.