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This marine animal is making researchers rethink the origin of the brain

Ancient comb jellies have a surprisingly advanced sensory organ that can be compared to an elementary brain.

This 3D image shows what the comb jelly Mnemiopsis leidyi looks like from above. The structure at the centre is the sensory organ that researchers find shockingly complex.

(Image: Alexandre Jan)

Marion Lebouvier Marion Lebouvier Marion Lebouvier Communications ADVISER

Linn Therese Nicolaysen Hauan Linn Therese Nicolaysen Hauan Linn Therese Nicolaysen Hauan COMMUNICATIONS ADVISER

Presented by: Presented by: Presented by: University of Bergen

Published 30 March 2026 - 00:01

New 3D images of the comb jelly’s sensory organ suggest that a form of brain may have emerged much earlier in Earth’s history than previously believed.

Comb jellies – also called ctenophores – are gelatinous animals that appeared in the oceans around 550 million years ago.

“Evolution seems to have invented centralised nervous systems more than once,” says researcher Pawel Burkhardt.

These delicate creatures have a specialised sensory structure called the aboral organ (AO). The organ helps them detect gravity, pressure, and light.

“We show that the AO is a complex and functionally unique sensory system,” says Pawel Burkhardt.

He is a researcher at the University of Bergen's Michael Sars Centre.

“Our study profoundly enhances our understanding of the evolution of behavioural coordination in animals,” he says.

“It is so unique”

To investigate how the aboral organ is built, the researchers used an advanced microscope to create detailed 3D models.

The images revealed 17 different cell types, 11 of which were previously unknown.

This large diversity of cells shows that the organ can detect several types of signals.

“I was immediately surprised by the diversity of cells in the aboral organ. It's an incredibly exciting discovery,” says Anna Ferraioli.

She is also a researcher at the Michael Sars Centre.

Researcher Anna Ferraioli is the lead author of the new study.

“AO has a striking complexity when compared to similar structures in other animal groups such as cnidarians and bilaterians. It is so unique,” she says.

Shares some similarities with modern brains

The findings show that the aboral organ is closely connected to the comb jelly’s nervous system.

The network of nerve cells and AO cells can communicate both through fast electrical signals and slower chemical signals.

Altogether, the comb jelly has a mixed system that combines multiple ways of transmitting signals.

“AO is definitely not like our brain, but it can be described as the organ ctenophores use as a brain. AO likely detects light and pressure, and helps the animals navigate in the water,” says Ferraioli.

The brain may have several evolutionary roots

The study was highlighted on the cover of Science Advances.

A key question in the evolutionary debate concerns which animal was the first to develop nerve cells on Earth.

Researchers continue to disagree on this.

But this study gives new support to the idea that nervous systems may have evolved more than once.

The researchers also examined the genes of comb jellies.

They found that many of the genes that control how the body is built in other animals are also found in comb jellies.

But their expression patterns are very different.

This may mean that the aboral organ is not related to the brain in other animals, but instead evolved independently, in its own unique way.

In other words, the brain may have multiple evolutionary roots rather than a single origin.

“Evolution seems to have invented centralised nervous systems more than once,” says Burkhardt.

More research is needed to understand the aboral organ even better.

“The next step is to uncover the roles of the newly identified cell types and examine more closely how AO influences the behaviour of the ctenophore,” says Ferraioli.

Reference:

Ferraioli et al. The 3D architecture of the ctenophore aboral organ and the evolution of complex integrative centers in animals, Science Advances, 2026. DOI: 10.1126/sciadv.aea8399

About the study

The researchers examined how the ctenophore’s sensory organ is built and how it is connected to the animal’s nervous system.

The findings show that the organ is far more complex than previously thought and resembles an elementary brain.

Its gene expression is completely unique, suggesting that ctenophores may have developed a centralised nervous system independently of other animals.

The findings challenge the idea that brains have a single evolutionary origin.

The study does not suggest that the human brain descends from ctenophores, but it expands our understanding of how brains may have evolved across different groups of animals.