Scientists from Berlin Museum of Natural History published an article in Scientific progressshows that sea urchins have a much more complex nervous system than previously thought.
Researchers found that their bodies function as a single nerve center, with an extensive nerve network and light-sensitive cells reminiscent of the structure of the human eye.
“Our data demonstrate that animals without a classical brain can still develop a nervous system with an organization similar to the brain. This fundamentally changes ideas about how a complex nervous system can develop,” said study lead author Jack Ulrich-Luther.
Head all over the body
The sea urchin at first glance is a simple, spiny inhabitant of the seafloor, which turns out to be essentially “the brain of the entire body.” An extensive nerve network covers all parts of the body and specialized photoreceptors on the surface allow the organism to sense light. This structure makes sea urchins an unusual example of an animal with brain function distributed throughout the body rather than concentrated in one central area.
Using modern methods to analyze individual cells and study gene activity, scientists have discovered that the body of adult sea urchins has an unusual structure. Almost the entire body functions as a “head”: genes that shape the body in other animals are active in sea urchins only in internal organs, such as the intestines and the water vascular system. They have no real body parts – their entire body is covered with a network of branching nerves and light-sensitive cells.
The researchers emphasize that the sea urchin's neural network is not chaotic. It is a highly organized structure with many types of neurons and neuropeptides capable of performing complex signaling functions.
Radical body restructuring
A special feature of sea urchins and their relatives such as starfish is the change in symmetry during development. Initially, these animals have bilateral symmetry, but as they mature, they undergo a “radical metamorphosis,” forming a five-rayed structure.
Researchers became interested in how one genome could support two very different body plans. To do this, they studied sea urchins immediately after metamorphosis, determining which cells and genes caused such dramatic changes. It turns out that branched neural networks play an important role.
Light and feeling of peace
Photoreceptors on the surface of sea urchins suggest that the animals are capable of sensing light, and their nerve clusters function like a distributed brain. These cells can combine different proteins to sense and process light signals.
“These results allow us to reconsider the idea of the 'simplicity' of sea urchins. Their nervous system is much more complex than previously thought, and their ability to perceive the world is broader,” Ulrich-Luther added.
New understanding of evolution
The researchers' work demonstrates that the evolution of the nervous system can follow different paths. Sea urchins show that complex cognitive and information processing functions can exist without a centralized brain. A distributed network of neurons and the presence of photoreceptors provide coordination of movement, response to light, and perhaps a more complex perception of the environment than might be expected.
The scientists note that their discovery is just the beginning. Science still doesn't know much about sea urchins' sensory and cognitive abilities.
“We may only be seeing the tip of the iceberg,” Ulrich-Luther concluded.
