Chop Off This Worm’s Head and It Can Still Detect Light

By Joanna Klein

The planarian flatworm is a smooshed noodle of an organism that can be found all over the planet. It has a triangular head occupied by a rather primitive version of a brain and two black dots for eyes. You can chop off this head, and it will grow back in about a week — eyes, brain and all. And you can hack away at the critter until all that’s left is a tiny speck of worm dust — and the thing will still grow back.

But now this peculiar creature, famous for its regenerative abilities (like when some grew two heads in space), may have another unforeseen idiosyncrasy: It not only reacts to light after decapitation, but it gradually recoups an ability to see finer aspects of light as its eyes and brain grow back. And despite lacking the machinery to see colors, the worm somehow creates a workaround, essentially converting “this rainbow colored world to a grayscale,” said Akash Gulyani a multidisciplinary scientist at the Institute for Stem Cell Biology and Regenerative Medicine in Bangalore, India, who led the study.

His team’s findings, published last week in Science Advances, could offer new opportunities for studying how animals recover after injuries and reveal additional details about function to the story of how animal eyes evolved.

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