If you’ve ever stared at one of the ocean’s more bizarre creatures, like, say, a sea urchin, and wondered where it keeps its brain, and what its brain even looks like? Well, according to new research, you’re looking at it.
Sea urchins are basically all brain, from spikey spines down to their gelatinous cores. Even weirder: genetically, they’re not too dissimilar from us.
A team led by developmental biologist Periklis Paganos took a deep dive into the purple sea urchin’s metamorphosis, as it transforms from a free-swimming larva spiky thing to an underwater foot trap. As larvae, urchins are bilaterally symmetrical, like us. During puberty, they reorganize into a more radial symmetry, like a starfish.
When the researchers mapped which genes activate during this transformation, they discovered that while much of the urchin’s basic cellular structure stays consistent, the architecture of its neurons changes dramatically. The juvenile urchin’s body becomes a massive distributed neural network, an integrated system of specialized nerve cells spread everywhere, like a brain.
More than half of the identified cell clusters in the young urchin were neurons that expressed a wide variety of neurochemicals familiar to us, like dopamine, serotonin, GABA, glutamate, histamine, and tons of other neuropeptides. Again, a lot like our brains.
The study published in Science Advances suggests the sea urchin brain is something closer to a vertebrate head that’s been stretched across an entire body. The researchers describe it as an “all-brain” structure—a brain that’s definitely not absent, but not centralized, either. It’s everywhere at the same time.
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