Severed Sea Slug Head Can Regrow Its Body, Including Heart

Scientists at Nara Women’s University in Japan observed a strange phenomenon last year that would make many a lizard quite envious. Sea slugs’ heads can detach and regrow the entirety of their bodies, including their whole hearts. While the (very slow) show was undoubtedly amazing, the reason the underwater gastropods detach their heads in general is likely due to their being infested with parasites. Which is less amazing, and more…disgusting.

Science News reported on the recent discovery, which the scientists at the university witnessed by happenstance. The scientists, who outlined their findings in the journal Current Biology, say they weren’t expecting to observe the sea slugs in their lab detach their own heads and regrow their entire bodies, and were shocked to see it happen over the course of 20 days.

“We were really surprised to see the [first] head crawling,” Yoichi Yusa, a co-author of the study, told Science News. Yusa added that this is the first-ever example of “whole-body” regeneration in any sea slug as far as she knows.

The sea slugs that demoed their ability to self-decapitate and re-proliferate were two species of sacoglossan sea slug; a.k.a. “sap-sucking” sea slugs. Sacoglossans are a clade of organisms (that is, a group of organisms descendent from a common ancestor), consisting of small sea slugs and sea snails, as well as marine gastropod mollusks, native to, amongst other places, the central Pacific Ocean. As you can see, they look like they combine a snail’s head and a leaf-like body.

Sayaka Mitoh / Science News 

Science News notes that it takes several hours for these sea slugs to rip their heads from their bodies, which means it’s probably not a defense mechanism against predators. Instead, the ability to cut and run, as it were, is likely an effective way of heading off parasite infestations. Apparently in the scientists’ batch of slugs, the ones that hit the ol’ head-ejection button had infestations of copepods; that is, microscopic crustaceans. (Sheldon J. Plankton from SpongeBob, incidentally, is a copecod.)

While other creatures can regenerate limbs, the scientists say these particular sap-suckers are special because their bodies are relatively complex, and even include hearts. Planarians, which are underwater flatworms, can also regrow their whole bodies, but are much simpler physiologically.

As for how exactly these sacoglossans are able to regenerate so fully, that remains a bit of a mystery. Scientists are aware of a groove in the slugs’ heads, which certainly helps them to separate from their bodies. But the real trick to their spectacular separations likely comes from their ability to consume and maintain chloroplasts from plants, which they can use to photosynthesize light into energy. Meaning these slugs can not only pack light, but also get by almost entirely on solar power.

Feature image: Sayaka Mitoh/ Science News