These Sea Slugs Can Sever Their Own Heads and Regenerate Fresh New Bodies

The slugs use algae to stay alive long enough to regenerate.
Brad Bergan

Everyone has heard of creatures capable of losing and then regenerating a tail or limb. But scientists just discovered two species of the sacoglossan sea slug that can do something incredible: severing and then regrowing an entirely new body — complete with heart and other internal organs, according to a new study published in the journal Current Biology.

These sea slugs can sever their own heads and regenerate fresh new bodies

The researchers also think the sea slugs might use the photosynthetic ability of chloroplasts gathered from algae in their diet to stay alive long enough to regenerate.

"We were surprised to see the head moving just after autotomy," said Sayaka Mitoh of Japan's Nara Women's University, in a press release shared with Interesting Engineering (IE) under embargo. "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."

This discovery happened by what you are invited to call a "freak accident." Mitoh is a doctoral candidate in the lab of Yoichi Yusa. In the Yusa lab, students raise sea slugs from eggs to investigate their life-history traits — and, one day, Mitoh looked down to see something unexpected: a sacoglossan slug wiggling around without a body.

The researchers even saw one slug do this twice. Twice!

Researchers don't know why the sea slugs sever their own heads

In the report, researchers said the slug head, once separated from its heart and body, moved autonomously after separation. In days, the wound on the back of its head had closed. The bodiless heads of young slugs then fed on algae within hours, and began regenerating a heart within a week. In roughly three weeks, the process was complete, and the slugs had brand-new bodies.

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However, the bodiless heads of older slugs didn't feed on algae, and died in roughly 10 days. There were no cases where the decapitated bodies didn't regenerate a new head. But the recently-beheaded bodies did move, and reacted to being touched for several days, sometimes for months.

As of writing, neither Mitoh nor Yusa are sure how the slugs manage to cut their own heads off. But they suspect the slugs use stem-like cells at the sliced end of their tiny necks to enable the regeneration of the body.

The researchers also aren't sure why a sea slug would sever its own head. One idea suggests they do this to help remove internal parasites — which inhibit reproduction. The researchers also don't know what triggers the slugs to remove their bodies — obviously a pressing subject for future studies.

Sea slugs present scientists with a new form of autotomy

This type of sea slug was already unique in its ability to integrate chloroplasts from algae into their own bodies — a process called kleptoplasty, which gives animals the ability to fuel their bodies via photosynthesis. This ability could help the slugs survive after autotomy — which is self-removal of part or all of the body — long enough to regenerate the cast-off body.

"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," said Mitoh in the embargoed press release shared with IE. "Such studies are almost completely lacking, as most studies on kleptoplasty in sacoglossans are done either at the genetic or individual levels."

These latest findings have revealed a new kind of autotomy — according to which animals with complex body distributions shed most of their body. And while it may be discomforting for us to imagine shedding our own bodies — this could be the very early beginning of a future technology capable of artificially extending the life of body parts separated from vital organs. Maybe even for a human.

This was a breaking story and was regularly updated as new information became available.

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