Certain fish, insects, and other animals can regrow lost limbs. However, two types of gastrointestinal snails are true masters of regeneration: the animals living in the sea can completely renew their entire bodies except for their heads, as Japanese researchers working with Sayaka Mitoh from Nara Women’s University in Nara report in the journal Current Biology. The doctoral student owes her discovery in the laboratory to a happy coincidence.
While researching the animals, the Japanese observed one day how one of the snails only moved with its head – the animal had separated the rest of its body. The team discovered that one snail even did this twice.
“We were surprised to see the head move shortly after the autotomy,” writes Mitoh. Autotomy means shedding body parts that are then regenerated. “We thought that the snail without a heart and other important organs would soon die, but we were again surprised that it regenerated the whole body.”
The heads of relatively young snails would have started to eat algae after just a few hours. Within a week the heart started to grow back; after about three weeks the snails had a completely new body.
Headless bodies also moved for months
The researchers suspect that the animals take advantage of the photosynthesis of chloroplasts, which they ingest from the algae, in order to stay alive long enough to regenerate. Photosynthesis produces sugars that are used to generate energy.
The heads of older specimens, on the other hand, did not eat and died after about ten days, it said. Conversely, in none of the animals researched would the severed bodies have allowed a new head to grow back. However, the headless bodies would have moved and responded to touch for a few days and even months.
The researchers cannot explain how the animals do it. Mitoh suspects, however, that there are stem-cell-like cells at the end of the severed neck of the animals that allow the body to renew. It is also a mystery to the researchers why the snails behead at all. One possibility is that this helps the animals to get rid of parasites that inhibit their reproduction. Further research is needed to get answers to these questions.