Directions for teachers: Ask your students to read the online Science News article “A sea slug’s detached head can crawl around and grow a whole new body,” which explores how some sea slugs regenerate, and answer the following questions. A version of the story, “No body is no problem for detached sea slug heads,” appears in the April 10, 2021 issue of Science News.

1. What makes some Elysia sea slugs special?

At least two species of Elysia slugs can regrow their entire bodies from just their head — a first for any sea slug. 

2. How might the sea slugs detach their heads from their bodies?

The slugs seem to have a groove on the back of the head region that scientists think is where the break occurs.

3. Describe the sea slug regeneration process.

Sea slugs detach their heads from their bodies over several hours. The heads crawl around, snacking on algae, and regenerate their bodies over about 20 days.

4. What happens to the sea slugs’ abandoned bodies?

The detached bodies don’t regrow heads the way their former heads regrow bodies. Instead, the rejected bodies move around for days or months until they eventually die.

5. Why do scientists think the sea slugs regenerate? What evidence supports the scientists’ hypothesis?

Scientists suspect the slugs use regeneration to rid themselves of parasites. It takes hours for the heads to detach from the bodies, so that mechanism probably isn’t useful for escaping predators. Meanwhile, the abandoned bodies of regenerating wild sea slugs were covered in copepods.

6. What role might algae play in sea slug regeneration?

The sea slugs feed on algae and can keep the plant’s energy-producing chloroplasts alive inside their bodies for weeks. Scientists debate what the chloroplasts do for their sea slug hosts. But biologist Yoichi Yusa suspects the organelle gives the slugs an energy boost as they regenerate.

7. Identify a literary device used in the article and explain how the device relates to the story.

The author uses a pun, or a play on words. The pun is a play on the word “ahead” and phrase “a head.” The sea slugs may need extra energy to get ahead as well as more than a head, meaning a new body.