These sea slugs can self-decapitate and grow a new body

It turns out getting beheaded doesn’t mean automatic death for every animal.

Researchers discovered that two species of sea slugs, Elysia cf. marginata and Elysia atroviridis, can regrow their body after cutting off their own head, according to a study published Monday in Current Biology.

Some animals like these sacoglossan slugs, also known as sap-sucking sea slugs, can autotomize, which is when an animal sheds a body part voluntarily, said study author Sayaka Mitoh, doctoral student in the department of biological sciences at Nara Women’s University in Japan.

She said the research team couldn’t determine why the slugs shed vital body parts, but some animals do it to remove internal parasites that inhibit their reproduction, Mitoh said.

Five of the 15 laboratory-bred young Elysia cf. marginata slugs started to self-decapitate about 226 to 336 days after they hatched. They began feeding on algae within a few hours after losing their body parts and began to regenerate their heart within seven days. After 20 days, the slugs had regenerated their entire body.

Three of the 82 Elysia atroviridis slugs decapitated their bodies at the neck. Of those slugs, two of them regenerated their bodies within a week.

Not all the slugs were as lucky.

Older slugs — the Elysia cf. marginata slugs who were hatched 480 to 520 days prior to self-decapitation — did not feed and died within 10 days.

It might seem like a “silly” choice for the older slugs to sever their head from the body if they won’t survive, Mitoh said, but the “old ones will die soon anyway and there may be a chance of surviving and regenerating a parasite-free body.”

Mitoh isn’t sure how the slugs can live without some of their vital organs, “but they can live without a heart probably because their heads are small” and can intake oxygen from their body’s surface.

One of the slugs in the experiment was able to complete the regeneration process twice, but Mitoh said she also is not sure how the slug could do it.

The findings of the study were intriguing, said Ángel Valdés, professor and department chair of biological sciences at California State Polytechnic University, Pomona, who was not involved in the research.

“Other sacoglossan sea slugs can regenerate appendages or other parts of the body, but this is an extreme case,” Valdés said.

The sea slugs he has studied in the past also autotomize parts of their bodies, but rarely vital organs.

More needs to be learned about this phenomenon, both about the species in the experiment and other animals, Mitoh said.

“We want to study whether other species of sacoglossans have this ability to study the evolutionary pattern and process of such extreme autotomy and regeneration,” she said.

In addition to evolution, Valdés is also interested in going out into the field to see if he can repeat the results of the experiment.

“I am also curious about the molecular and physiological underlying mechanisms that allow the regeneration the body,” Valdés said.