Researchers led by Periklis Paganos built a single-cell gene-expression atlas of juvenile purple sea urchins and found that over half of the identified cell clusters are neurons. These neurons express a wide range of neurotransmitters, including dopamine, serotonin, GABA, glutamate, histamine and multiple neuropeptides. Metamorphosis from bilateral larvae to fivefold radial juveniles coincides with a major reorganization of neuronal types and distribution. The team describes this distributed, integrated nervous system as an 'all-body' brain, reshaping ideas about how complex nervous systems evolve.
Sea Urchins Discovered to Have an 'All‑Body' Brain — Nervous System Spread Throughout the Body
Researchers led by Periklis Paganos built a single-cell gene-expression atlas of juvenile purple sea urchins and found that over half of the identified cell clusters are neurons. These neurons express a wide range of neurotransmitters, including dopamine, serotonin, GABA, glutamate, histamine and multiple neuropeptides. Metamorphosis from bilateral larvae to fivefold radial juveniles coincides with a major reorganization of neuronal types and distribution. The team describes this distributed, integrated nervous system as an 'all-body' brain, reshaping ideas about how complex nervous systems evolve.
07:15 AM, 11/17/2025Science
Sea urchins possess a body-wide, brain-like nervous system, new study shows
Sea urchins may look like little balls of spikes in a tide pool, but new research shows their nervous systems are far more elaborate than previously believed. A team led by developmental biologist Periklis Paganos at the Stazione Zoologica Anton Dohrn in Italy mapped gene activity across cells in juvenile purple sea urchins (Paracentrotus lividus) and built a single-cell atlas that reveals an unexpectedly complex neural organization.
The study focuses on metamorphosis, when urchins transition from free-swimming, bilaterally symmetric larvae to fivefold radially symmetric juveniles. That dramatic body-plan change is accompanied by a deep reorganization of neuronal cell types: while many body cells reuse similar genetic programs before and after metamorphosis, neurons undergo a major shift in identity and distribution.
'Although the same genetic toolkit is used to generate neurons, the outcomes of the neurogenic program differ substantially between the two analyzed life stages,' the authors write.
The juvenile cell atlas showed that more than half of the identified cell clusters were neuronal. These neurons display a wide variety of molecular signatures and neurotransmitter systems familiar from vertebrates, including dopamine, serotonin, GABA, glutamate, histamine and diverse neuropeptides. Rather than a simple decentralized nerve net, the urchin nervous system appears organized with brain-like complexity distributed across the entire body.
Evolutionary biologist Jack Ullrich-Lüter of the Natural History Museum of Berlin commented that the findings demonstrate how animals without a conventional head-centered brain can still develop brain-like architectures. The work challenges the assumption that a complex nervous system requires a central brain and suggests alternative evolutionary routes to neural complexity.
Publication: The study was published in Science Advances and highlights how comparative, cellular-level maps of gene activity can reshape our understanding of nervous system evolution.