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Some sea slugs behead themselves and grow entirely new bodies

Regeneration is a common trait in animals: lizards shed their tails and grow a new one and axolotls can grow back their lost limbs!

But would you expect someone to stay alive after getting beheaded? No, right?

Turns out this isn’t the same for 2 species of sea slugs.

The head and body of a sea slug after it decapitated itself
The head and body of a sea slug after it decapitated itself (Image credits: Sayaka Mitoh)

Sacoglossan sea slugs - Elysia cf. marginata and Elysia atroviridis, can decapitate themselves, i.e shed their entire bodies and regrow a new one, including their hearts! They shed off their heads which continue to live without a heart or any organs while the discarded body eventually dies off.

This discovery was actually accidental, said biologists Sayaka Mitoh and Yoichi Yusa of Women’s University, Japan. They were observing the life cycle of sea slugs when they saw that one had shed its entire body.

Few hours after they dropped off their bodies, the young ones started feeding and began to regenerate their heart within seven days. Within just three weeks they had regenerated their whole bodies. One of the slugs even did it twice! Older slugs however did not feed and died within 10 days.

Growth of sea slug's head after it decapitated itself
From left to right: Day 0, day 7, day 14 and day 22 (Image credits: Sayaka Mitoh)

One can simply not help but wonder how the heads can survive when they’re totally detached from their hearts and other important organs. Sea slugs have this unique ability where they can incorporate chloroplasts from the algae they feed into their own bodies and use it to produce energy by carrying out photosynthesis. This fascination phenomenon is called kleptoplasty.

It isn’t sure how the slugs are capable of growing new bodies but biologists think it might have something to do with stem cells like cells at the cut end of their ends which can be capable of regenerating.

Although what triggers the slugs’ autotomy still remains unclear, one of the reasons could be parasite infestation. All the slugs that decapitated themselves were infested with parasites. But when they regenerated their bodies they were parasite free!

Researchers are planning new studies to understand more about this peculiar behaviour.



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