When sea slugs lose their heads, they keep calm and regenerate a whole new body.
Sayaka Mitoh and Yoichi Yusa at Nara Women’s University in Japan noticed that some sea slugs (Elysia spp.) could sever their entire bodies from their heads, which continued to move around and eat algae. A slug’s head regenerated a heart within a week and the entire body within three weeks. Slugs more than a year old did not have this ability — they simply died when their heads were severed.
The researchers found that the head splits off at a “breakage plane” in the neck, and the authors think the region contains stem cells that allow the body to regenerate. The disembodied heads cannot digest the algae they consume, and the researchers hypothesize that the heads rely for food on chloroplasts in the algae. These organelles use photosynthesis to make energy that can power the slug until its digestive system regenerates.
It’s unclear why slugs shed their entire bodies, although the researchers think it might be a way to rid themselves of parasites.