New research using a developmental cell atlas of the purple sea urchin Paracentrotus lividus reveals a diverse array of neurons that assemble into an integrated, bodywide nervous system during metamorphosis. Though not centralized like a vertebrate brain, the urchin's neural organization shows brain‑like features and includes light‑sensitive cells scattered across the body. These discoveries challenge assumptions about how complex nervous systems evolve and highlight alternative ways animals can sense and respond to their environment.
Sea Urchins Aren't Mindless — Their Whole Body Forms a Brain‑Like Nervous System
New research using a developmental cell atlas of the purple sea urchin Paracentrotus lividus reveals a diverse array of neurons that assemble into an integrated, bodywide nervous system during metamorphosis. Though not centralized like a vertebrate brain, the urchin's neural organization shows brain‑like features and includes light‑sensitive cells scattered across the body. These discoveries challenge assumptions about how complex nervous systems evolve and highlight alternative ways animals can sense and respond to their environment.
08:51 AM, 11/19/2025Science
New research shows sea urchins possess a far more elaborate, bodywide nervous system than scientists long assumed. Rather than being mere digestive sacks encased in spikes, many urchins develop a distributed, brain‑like organization of neurons during metamorphosis.
Who they are and how they live
Sea urchins belong to the phylum Echinodermata, a group that arose around the time of the Cambrian explosion and includes starfish, sand dollars, sea lilies and sea cucumbers. True urchins first appear in the fossil record roughly 450 million years ago. Today they inhabit seafloors from shallow reefs to the deep abyssal plain.
Externally, urchins are covered in movable spines and rows of tube feet that end in small suction pads. Internally they have a rigid calcium‑carbonate shell called a test and a unique chewing apparatus known as Aristotle's lantern, with five self‑sharpening teeth that scrape algae and other food from rock surfaces. Their digestive tract runs through the body and exits at an anus on the animal's upper surface. Predators include sharks, eels and sea otters, which are known to pry urchins from rocks and crack them open with stones.
What the new study found
Researchers mapped cell types in the purple sea urchin Paracentrotus lividus to build a developmental cell atlas, tracking how neurons and other cells arise during the animal's dramatic transformation from a bilateral larva to a fivefold‑symmetric adult. The atlas revealed a rich diversity of neuronal cell types that differentiate and integrate into a bodywide nervous system as metamorphosis progresses.
Although the urchin nervous system is distributed rather than concentrated in a single brain, its internal organization shows parallels to aspects of vertebrate brain architecture. The team also identified light‑sensitive cells scattered across the body and large regions of nervous tissue that respond to light, suggesting that visual cues help regulate parts of the nervous system even though urchins lack conventional eyes.
'Our results show that animals without a conventional central nervous system can still develop a brain‑like organization,' said study author Dr. Jack Ullrich‑Lüter.
Why it matters
These findings broaden how biologists think about the evolution of complex nervous systems: sophisticated sensory processing and coordinated behavior can arise in bodywide, distributed architectures as well as in a centralized brain. The work opens new lines of inquiry into how neural and sensory systems evolve, how non‑centralized nervous systems process information, and how simple animals interact with their environment.
Future studies will explore how these distributed neural circuits control specific behaviors, how light sensitivity affects urchin activity, and whether similar organizational patterns appear in other echinoderms or invertebrate lineages.