If Your Hands Could Smell, You’d Be an Octopus

Hundreds of powerful suckers on octopus arms do more than just stick. They actually smell and taste too. (Josh Cassidy/KQED)

Everyone knows that an octopus has eight arms. And similar to our arms, it uses them to grab things and move around. But that’s where the similarities end. Hundreds of suckers on each octopus arm give them abilities people can only dream about.

At the Aquarium of the Bay in San Francisco, the Giant Pacific octopuses sometimes can be seen stretching out all eight arms at the same time. Each arm has up to 240 suckers running up and down its length.

“When there’s food in the water, and they’re ready for it,” said aquarist Alex Reiss, “they’ll have their arms stuck out like a flower, trying to get as much surface as possible.”

But the octopuses aren’t just using their arms to grab fish.

“The suckers are hands that also smell and taste,” said Rich Ross, senior biologist and octopus aquarist at the California Academy of Sciences across town. “They’re smelling the water with their suckers.”

Suckers are “very similar to our taste buds, from what little we know about them,” said University of North Carolina, Chapel Hill cephalopod biologist William Kier.

A Larger Pacific striped octopus at the California Academy of Sciences, in San Francisco, pushes an empty shell away. The suckers on their arms, which can smell and taste, help octopuses find food.
A Larger Pacific striped octopus at the California Academy of Sciences, in San Francisco, pushes an empty shell away. The suckers on their arms, which can smell and taste, help octopuses find food. (Josh Cassidy/KQED)

If these tasting, smelling suckers make you think of a human hand with a tongue and a nose stuck to it, that’s a good start to understanding just how differently octopuses are organized than humans. It all stems from the unique challenges an octopus faces as a result of having a flexible, soft body.

“This animal has no protection and is a wonderful meal because it’s all muscle,” said Kier.

So the octopus has adapted over time. It has about 500 million neurons (dogs have around 600 million), the cells that allow it to process and communicate information. And these neurons are distributed to make the most of its eight arms. An octopus’ central brain – located between its eyes – doesn’t control its every move. Instead, two thirds of the animal’s neurons are in its arms.

“It’s more efficient to put the nervous cells in the arm,” said neurobiologist Binyamin Hochner, of the Hebrew University of Jerusalem. “The arm is a brain of its own.”

This enables octopus arms to operate somewhat independently from the animal’s central brain. The central brain tells the arms in what direction and how fast to move, but the instructions on how to reach are embedded in each arm. Octopus arms can also work autonomously when they’re searching, like when they’re looking for food under a rock.

“The strange morphology of the octopus is part of an evolutionary process to enable highly complex behavior in a soft body,” said Hochner. “Everything developed in a different way to really enable the animal as a whole to create a rich behavior.”

A Day octopus in its tank at the California Academy of Sciences, in San Francisco. Octopuses have hundreds of suckers up and down the length of each arm.
A Day octopus in its tank at the California Academy of Sciences, in San Francisco. Octopuses have hundreds of suckers up and down the length of each arm. (Josh Cassidy/KQED)

Octopuses have also evolved mechanisms that allow their muscles to move without the use of a skeleton. This same muscle arrangement enables elephant trunks and mammals’ tongues to unfurl.

“The arrangement of the muscle in your tongue is similar to the arrangement in the octopus arm,” said Kier.

In an octopus arm, muscles are arranged in different directions. When one octopus muscle contracts, it’s able to stretch out again because other muscles oriented in a different direction offer resistance – just as the bones in vertebrate bodies do.

Inside each sucker is a chamber called the acetabulum (shown here in a drawing). The octopus contracts muscles in the wall of this chamber to create the sucker’s powerful grip.
Inside each sucker is a chamber called the acetabulum (shown here in a drawing). The octopus contracts muscles in the wall of this chamber to create the sucker’s powerful grip. (Teodros Hailye and Josh Cassidy/KQED)

This skeleton of muscle, called a muscular hydrostat, is how an octopus gets its suckers to attach to different surfaces. Each sucker first creates a water-tight seal. Then the octopus contracts strong muscles to expand the sucker’s water-filled chamber. This lowers the pressure inside. The higher pressure outside pushes against the sucker and creates its powerful grip.

Ellen Umeda, aquarist at the Monterey Bay Aquarium, pulls a Giant Pacific octopus arm off her own arm.
Ellen Umeda, aquarist at the Monterey Bay Aquarium, pulls a Giant Pacific octopus arm off her own arm. (Josh Cassidy/KQED)

Octopus keepers at aquariums everywhere are intimately acquainted with that grip. At the Monterey Bay Aquarium recently, a reddish Giant Pacific octopus slid an arm outside its tank and wrapped it around aquarist Ellen Umeda’s arm.

“It’s a very unusual sensation. It feels like a bunch of suction cups slowly working up your arm,” said Umeda. As she carefully removed the arm, each sucker made a distinct sound, something like a loud slobbering kiss, and a line of red dots appeared on her arm.

“The hickies feel a little sore, like any other bruise,” she said. “This may sound painful, but the octopus’ curiosity and excitement make up for it.”

If Your Hands Could Smell, You’d Be an Octopus 28 April,2017Gabriela Quirós

  • Hillary Clintub

    Use genetic engineering to make it happen. Personally, though, I’d rather have eyes that could perceive more than just the three basic colors over hands that can smell. I’d like to be able to see the ultraviolet and infrared parts of the color frequency spectrum.

    • Gabriela Quiros

      Hi Hillary. I wrote this story and produced this video. If you’re interested in animals that see differently than us, you might like the video Deep Look produced about mantis shrimp. They can perceive circular polarized light. Inspired by the mantis shrimp’s eyesight, researchers are working on polarization cameras that would constitute a giant leap for early cancer detection. You can watch the video and read the article by my colleague Elliott Kennerson here: https://ww2.kqed.org/science/2016/11/15/the-snail-smashing-fish-spearing-eye-popping-mantis-shrimp/
      Thank you for your comment!
      All best, Gabriela.

      • Hillary Clintub

        Thanks, Gabriela. I read a book on epigenetics a year or five ago and one of the chapters was about vision. It mentioned the mantis shrimp as well as several other animals that have enhanced vision compared to humans due to them having a greater variety of cones in their retinas. Of course, they also have developed brain areas to correspond to those unique sensors. I think about that every time I hear about someone with synesthesia. That actually sounds like it could be a GOOD thing to have to me.

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Gabriela Quirós

Gabriela Quirós is a video producer for KQED Science and the coordinating producer for Deep Look. She started her journalism career more than 20 years ago as a newspaper reporter in Costa Rica, where she grew up. She won two national reporting awards there for series on C-sections and organic agriculture, and developed a life-long interest in health reporting. She moved to the Bay Area in 1996 to study documentary filmmaking at the University of California-Berkeley, where she received master’s degrees in journalism and Latin American studies. She joined KQED as a TV producer when its science series QUEST started in 2006 and has covered everything from Alzheimer’s to bee die-offs to dark energy. She has won three regional Emmys and has shared awards from the Jackson Hole Wildlife Film Festival, the Society of Professional Journalists and the Society of Environmental Journalists. Independent from her work in KQED's science unit, she produced and directed the hour-long documentary Beautiful Sin, about the surprising story of how Costa Rica became the only country in the world to outlaw in vitro fertilization. The film aired nationally on public television stations in 2015.

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