These Self-Decapitating Sea Slugs Can Regrow An Entire Body On Their Old Head


Rachael Funnell

Social Editor and Staff Writer

clockMar 8 2021, 16:12 UTC
self-decapitating sea slug

No body? No problem. Image credit: Sakaya Mitoh

When you think of slugs you might not imagine great things, but a recent discovery published in the journal Current Biology has found that some marine varieties can do something pretty incredible. The study identified two varieties of sea slug that are able to decapitate themselves and from their severed head grow a new body, like it’s no big deal.

The serendipitous finding occurred while PhD candidate Sakaya Mitoh of Nara Women’s University in Japan was documenting the development stages of sea slugs in a lab. One day, Mitoh noticed a severed head that was still moving despite being separated from the heart and other vital organs. Expecting it would soon wither away, you can only imagine her surprise when she later returned to the drifting head and found it had a new body.


Lizards are famous for their regeneration skills, dropping their tails when under threat and growing another (or sometimes more) in its place. It seems then that their time as the poster child for regeneration may be up, with two species of sacoglossan sea slug being able to replace a heck of a lot more than a tail.

So how on Earth does a decapitated head make it in the big ocean? Without the traditional means of digestion, the researchers realized the heads must be doing something else to stay alive while they cook up slug-bod 2.0. They posit that the slugs may be monopolizing on the photosynthetic ability of chloroplasts, which they incorporate into their tissues by monching on algae (a phenomenon known as kleptoplasty). If true, the theory suggests they live like a leaf to survive long enough for their second body to bloom.

It must’ve been a strange time indeed for Mitoh and colleagues at the lab of Yoichi Yusa where the mysterious self-decapitating sacoglossans were first observed performing their unique magic trick. The researchers reported that after the slugs hit the head ejector button (a process of casting off a body part known as autotomy) it would take a few days for the wound at the back to close. The head would be moving from the moment it went solo and its success from here depended on the age of the sea slug.

The severed heads of young sea slugs started eating within a few hours. Image credit: Sakaya Mitoh

The decapitated heads of older slugs usually died within 10 days, while the younger slugs’ heads began feeding on algae within a few hours and got to work on a new heart within a week. Three weeks down the line, the regeneration was complete. It’s possible the remarkable feat is facilitated by stem-cell-like cells that have the capacity to become anything in the body. Exactly why they do it is another question, though it could be a means of jettisoning parasitized bodies. The researchers plan to study the slugs with hopes they’ll be able to confirm exactly how and why such a complex animal can regrow almost its entire self.