Some of the most interesting—and possibly strangest—scientific discoveries happen by accident. According to the New York Times, Sayaka Mitoh, a Ph.D. candidate at Nara Women's University in Japan, was studying the life history of sea slugs when she stumbled upon something bizarre.
One of her captive-raised sea slugs had somehow been decapitated, and the head seemed to be moving around and eating. Then, as the Times reports, she realized that the slug itself initiated the decapitation. While self-amputating limbs are not unheard of for some organisms, the self-amputation of an entire body had not yet been observed. The video below from Live Science summarizes this unique discovery.
As Mitoh stated to the Times, "I was really surprised and shocked to see the head moving." She also says that she expected it to die quickly without major organs needed to survive. Not only did it survive, but the Times reports that it regenerated most of its body within three weeks.
This random incident encouraged Mitoh to investigate this extreme form of self-amputation. The results of this work were published earlier this week in Current Biology. According to the study, the two species of sacoglossan sea slug (Elysia marginate and Elysia atrovirdis) undergo "a new type of extreme autonomy." They shed their main body and regenerate a new one—including the whole head. Additionally, the study reports that the shed body does not regenerate a head. According to the Times, some detached bodies remained reactive to stimuli for months until they finally decomposed.
The New York Times reports that the head wound where the detachment occurred healed within one day. The heart regenerated in about one week, and most sea slugs completely regenerated within three weeks. Additionally, these particular sea slugs can sustain themselves through photosynthesis, which likely allows them to survive without the rest of their vital organs for extended time periods.
Because this process occurs too slowly to be a predator defense mechanism, the Times reports that the team suspects the body detachment occurs if the slug has a parasitic infection. However, only one of the two species studied had parasites.
While this study confirmed these two species' extreme regeneration capabilities, the exact mechanism of this process is yet to be determined. The Times reports that Mitoh is hopeful that this process could lead to advancements in regenerative medicine.