Imagine the biologist Sayaka Mitoh’s surprise the day she discovered that a sea snail in her lab suddenly lacked her body. Or his head, really – it depends on your perspective. Anyway, the sea snail was in two pieces, both seemed to be alive, in the sense that they were both still moving. Somehow, they continued to live for days, and then weeks, even though the head was minus the heart and digestive system.
Among biologists, this type of body-splitting maneuver is known as autotomy – lizards, for example, lose their tails to escape predation. But what the great sacoglossan slug does later places it in its own class. “We were surprised to see his head moving right after the autotomy,” says Mitoh. “I thought he would soon die without a heart and other important organs, but we were again surprised to find that it regenerates the whole body.”
That’s right: he shot a Deadpool. Just hours after self-decapitation, the head began to crawl to feed. One day, his neck wound had healed. After a week, his heart began to regenerate. In less than a month, the whole body grew again, and the bodyless slug incarnated once more. Several slugs did this in Mitoh’s lab, so this is a feature, not an error. A slug – apparently a show-off – even self-beheaded twice.
However, previously held bodies fail. As Mitoh states in a new paper, which describes the phenomenon in the journal Current biology, “The bodies gradually shrank and became pale, apparently due to the loss of chloroplasts, and eventually decomposed. The heartbeat was visible just before the body decomposed. ”
Now, before we get to the question of why a sea slug would decapitate on Earth, let’s talk about How, and those chloroplasts. Mitoh actually observed this behavior in several individuals from two different species of sacoglossan sea slug. This group of mollusks is famous – at least among biologists – for “kleptoplasty”, or the way they steal their energy source. In the algae that animals eat, photosynthesis hums in structures known as chloroplasts. Instead of digesting them, the sea snail actually incorporates them into its own tissues. These chloroplasts can remain photosynthetically active for months, allowing their adoptive sea snail to attract energy from the sun. The animal is fed a lot of solar energy.