Sea Slug Species Sever Their Own Heads to Grow New Bodies

Talk about the wonders of nature.

This image shows the head and the body of Elysia cf. marginata, a day after autotomy. The shed body is much heavier (>80% of the total weight) than the head. (Credit: Sayaka Mitoh)

(CN) — Though some animals such as starfish and salamanders can regrow lost limbs or tails, scientists announced Monday the discovery of sea slugs capable of regenerating an entirely new body.

“We were surprised to see the head moving just after autotomy,” said Sayaka Mitoh, of Nara Women’s University in Japan, in a statement. “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.”

In a study published in the journal Current Biology, researchers detailed the regenerative ability of two species of sacoglossan sea slugs that are able to grow new bodies, including internal organs.

Mitoh said the discovery was made serendipitously while studying the life history traits of the sea slugs.

“One day, Mitoh saw something unexpected: a sacoglossan individual moving around without its body. They even witnessed one individual doing this twice,” the statement said.

Immediately after the head of the sea slugs were detached from their bodies, they began moving on their own. Their wounds closed up in a matter of days, while they began to eat algae within hours of separation. Within the span of a week, the heart began to regenerate. In less than a month, the body had fully regrown.

The researchers suspect the slugs are able to survive by using the photosynthetic ability of chloroplasts found in the algae they eat, a process called kleptoplasty. Notably, the separated heads that didn’t eat usually died after 10 days. As for the slugs’ original bodies, they failed to grow new heads, but could move and react to touch for up to months.

While the researchers aren’t exactly clear how sea slugs are able to regenerate so much of their bodies, they suspect stem-like cells at the end of the neck are responsible. They added that much more research must be done to understand the slugs’ amazing regenerative abilities.

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

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