Sea slug can decapitate itself and regrow its entire body including organs, say ‘surprised’ scientists

In the vast realm beneath the surface of our planet’s oceans, spectacular mysteries still abound. Creatures we think we understand suddenly surprise us with new - and in this case - hair-raising behaviours.

Japanese scientists have discovered a type of sea slug which is capable of cutting off its own head, and not only somehow surviving, but then regenerating a whole new body, including organs.

While autotomy - the process of casting off a body part - is relatively well-known in the animal kingdom, such as lizards losing their tails to escape predators, this extreme form of self-decapitation is unprecedented.

And it is not just one species of sea slug where this extraordinary adaptation has been found, but two.

Scientists at Nara Women’s University in Japan, said they were first alerted to the phenomenon when they saw “something unexpected”: a slug they had in their laboratory was slithering around without its body. Or rather, just the head was slithering around, and continuing to feed.

The researchers report that the head, separated from the heart and body, moved on its own immediately after the separation.

Within days, the wound at the back of the head closed. The heads of relatively young slugs started to feed on algae within hours. They started regeneration of the heart within a week. Within about three weeks, regeneration was complete.

However, despite slugs of various ages apparently giving the self-decapitation technique a go, not all of them survived. The heads of older individuals didn’t feed and died in about 10 days, the researchers said.

In either case, the headless bodies didn’t regenerate a new head, however, despite being decapitated, many continued to move and/or react to being touched for several days or even months.

Sayaka Mitoh of Nara Women’s University said: “We were surprised to see the head moving just after autotomy.

“We thought that it would die soon without a heart and other important organs, but we were surprised again to find that it regenerated the whole body.”

The scientists said they aren’t sure how the sea slugs are capable of such an extensive regeneration. But Ms Mitoh suggested there must be “stem-like cells” at the cut end of the neck that are capable of regenerating the body.

They also don’t know exactly why the slugs do this. They said one possibility is that it helps to remove internal parasites that inhibit their reproduction.

Furthermore, they also don’t know what immediate cue prompts the slugs to cast off the rest of the body, and said these are areas for future study.

The sea slugs in question were already the subject of scientific intrigue because they are able to incorporate chloroplasts from algae they eat into their own bodies, an adaptation known as kleptoplasty.

This process gives the animals an ability to fuel their bodies by photosynthesis.

The scientists suggested this rare capability might help them survive after they remove their own heads long enough to regenerate a new body.

They said: “These findings in sea slugs represent a new type of autotomy in which animals with complex body plans shed most of their body.”

Ms Mitoh said: “As the shed body is often active for months, we may be able to study the mechanism and functions of kleptoplasty using living organs, tissues, or even cells.

“Such studies are almost completely lacking, as most studies on kleptoplasty in sacoglossans are done either at the genetic or individual levels.”

The research is published in the journal Current Biology.