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‘Cute and weird’ sea slugs lose their heads

AP, March 11, 2021 7:00PM Kids News

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Japanese sea slug (Elysia cf. marginata) before it loses its head. Picture: Sayaka Mitoh via AP media_cameraJapanese sea slug (Elysia cf. marginata) before it loses its head. Picture: Sayaka Mitoh via AP


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Scientists have discovered the ultimate case of regeneration*: Some decapitated* sea slugs can regrow hearts and whole new bodies.

This “wonder of nature,” reported in a biology journal this week, could eventually help scientists better understand and tackle regeneration of human tissue*.

Biology researcher Sayaka Mitoh said she loves studying Japanese sea slugs because they are small, cute and weird. They can even briefly photosynthesise* like a plant making food from sunlight.

One day in the lab, she saw something bizarre: A sea slug had decapitated itself and the head kept on moving and living. Then a couple more did the same, according to a study in Current Biology.

So the doctoral* student and Nara Women’s University aquatic ecology professor Yoichi Yusa tried it themselves, cutting the heads off 16 sea slugs. Six of the creatures started regeneration, with three succeeding and surviving. One of the three even lost and regrew its body twice. Two different species of Japanese sea slugs did this regeneration trick.

This undated photo provided by Sayaka Mitoh shows a Elysia cf. marginata sea slug after autotomy. According to a study released in the journal Current Biology on Monday, March 8, 2021, scientists have discovered that some Japanese sea slugs can grow whole new bodies if their heads are cut off, taking regeneration to the most extreme levels ever seen. (Sayaka Mitoh via AP) media_cameraElysia cf. marginata sea slug after autotomy. Picture: Sayaka Mitoh via AP

Other creatures can cast off body parts when needed, like when some lizards drop their tails to get away from a predator, in a biological phenomenon* called autotomy.

“We think that this is the most extreme case of autotomy,” Prof Yusa said. “Some animals can autotomise their legs or appendages* or tails, but no other animal shed their whole body.”

Scientists had thought that such a relatively large animal — one of the sea slug species can grow to 15cm long — couldn’t survive without a heart to pump blood and nutrients to the brain, said Canadian marine biologist Susan Anthony, who wasn’t part of the study.

But the same thing that makes this species spectacular is probably what helps it pull off the trick, said Dr Anthony and Prof Yusa.

When these sea slugs eat a certain type of algae they can photosynthesise their food from sunlight and oxygen, just like a plant, for about 10 days, Prof Yusa said. What’s probably happening after decapitation is that the head sort of acts like a plant, he said. It turns a shade of green and gets its energy from oxygen and sunlight. The fact that it becomes tiny helps, he said.

These species probably developed the feat as a way of fighting off parasites, Ms Mitoh and Prof Yusa said.

Decapitated sea slugs can regrow body

Humans may be able to learn something useful from the sea creatures, several scientists said. What’s especially intriguing is that these sea slugs are more complex than flatworms or other species that are known to regenerate, said Nicholas Curtis, a biology professor at Ave Maria University who wasn’t part of the study.

“It is of course a wonder of nature, but understanding the underlying molecular mechanisms involved could help us to understand how our cells and tissues can be used to repair damage,” Prof Curtis said.


  • regeneration: growing back
  • decapitated: having its head cut off
  • tissue: group of similar cells together, such as skin
  • photosynthesise: how green plants make food from sunlight, carbon dioxide and water
  • doctoral: study that leads to being awarded the title of Doctor of Philosophy
  • phenomenon: something we notice
  • appendages: a small thing attached to a larger thing


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Animals with superpowers need your help


  1. How does Sayaka Mitoh feel about sea slugs?
  2. How many Japanese sea slugs were found to have this ability?
  3. What does autotomy mean?
  4. How big can one of the sea slug species grow?
  5. What’s a likely reason for snugs to be able to do this?


1. Write a Reply
If someone said to you, ‘studying sea slugs would be the most boring, useless thing in the world’, what would you say to them?

Write your reply. Include lots of details to make your answer very convincing!

Time: allow 20 minutes to complete this activity
Curriculum Links: English, Science

2. Extension
Do you think that scientists could ever find a way to give humans the ability to autotomise? Brainstorm some ideas about how they might try to do this. Use information in the story to help you.

Time: allow 15 minutes to complete this activity
Curriculum Links: English, Science, Critical and Creative Thinking

An adjective is a describing word. They are often found describing a noun. To start with look at the words before the nouns.

Search for all the adjectives you can find in the article

Did you find any repeat adjectives or are they all different?

Extension: Pick three of your favourite adjectives from the text and put them in your own sentences to show other ways to use them.

Have you used any in your writing?

Extra Reading in animals