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Just in: Jellyfish Can Learn Despite Not Having Brains

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Jellyfish – those undulating, translucent creatures often associated with the ocean’s depths – have always been the poster children for simplicity in the animal kingdom. They float through the water, pulsating like nature’s own lava lamps, their gelatinous bodies seemingly devoid of any advanced cognitive ability.

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But guess what? The world of science has a tendency to shatter our preconceived notions, and it turns out that even these seemingly simple creatures can surprise us. In a groundbreaking study, researchers have revealed that Caribbean box jellyfish can learn from experience, even though they lack a central brain. This discovery has sent shockwaves through the scientific community and is redefining our understanding of learning and adaptation in the animal kingdom.

The Pinnacle of Nervous System Performance

“Learning is the pinnacle of nervous system performance,” asserts Jan Bielecki, a scientist at Kiel University in Germany. Traditionally, when we think of learning, we conjure images of classrooms, books, and intricate neural networks. We picture mice navigating mazes, birds memorizing flight paths, and primates mastering complex puzzles.

Jellyfish in the Spotlight

Enter the humble jellyfish. These delicate, often ethereal creatures represent a very early stage in animal evolution. They have been swimming in our oceans for hundreds of millions of years, long before the dinosaurs roamed the Earth. But despite their ancient lineage, we’ve never credited them with the ability to learn. That’s where the paradigm-shifting research of Bielecki and his colleagues comes into play. They decided to investigate the learning capabilities of jellyfish, throwing open the doors to a world of unexpected discoveries.

Recreating the Natural Habitat

To delve into the minds of jellyfish, the researchers set up an experiment that mimicked the Caribbean box jellyfish’s native mangrove-rich habitat. These waters are the natural playground of the Tripedalia cystophora, a jellyfish species barely the size of a fingernail.

They placed these tiny jellyfish into a round tank, which might sound ordinary, but it was anything but. The tank’s walls were adorned with a mesmerizing pattern of white and grey stripes, cleverly designed to replicate the vertical mangrove roots that the species navigates in the wild.

A Visual Illusion

But here’s the kicker – the grey stripes weren’t black. This optical illusion made the ” mangrove roots” appear farther away than they actually were. Consequently, the jellyfish bumped into the tank walls. Ouch!

But here’s where things get really interesting.

@Rickard Zerpe

Learning at the Speed of Light (Well, Almost!)

After just a seven-and-a-half-minute session in this striped tank, each of the 12 intrepid jellyfish subjects began to pivot and swerve, deftly avoiding the walls. It was as if they had learned from their collisions and adjusted their behavior accordingly. By the time the experiment concluded, these jellyfish had slashed their crashes in half and quadrupled their successful swerves.

Jan Bielecki himself couldn’t contain his amazement. “After bumping into these stripes that were closer than they thought,” he exclaimed, “they learned to stay further away from them.” What’s even more mind-boggling is that this learning process happened in just a few minutes. It’s like teaching a dog a new trick during a coffee break!

The Anatomy of Jellyfish Learning

So, where does this learning happen in a jellyfish’s mysterious, brainless body? Well, it seems that they’ve managed to turn their lack of a traditional brain into an advantage. Learning, it turns out, occurs in the jellyfish’s four visual sensory organs, named rhopalium. These rhopalia are embedded throughout the jellyfish’s body, and each one is like a mini learning hub.

Picture this: Each rhopalium boasts six lenses that sense light. That’s a whopping total of 24 eye-light lenses distributed strategically throughout the jellyfish. These lenses are more than just the creature’s window to the underwater world; they are its guides, helping it navigate the aquatic realm.


In the depths of the ocean, where light struggles to pierce the veil of darkness, jellyfish are showing us that learning doesn’t always require a brain. The discovery that Caribbean box jellyfish can adapt and learn from experience challenges long-held beliefs about the limits of cognition in the animal kingdom. With their visual sensory organs, the rhopalia, these elegant, brainless wonders are redefining the rules of learning.

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