Thread by @WIRED

For most organisms, decapitation is a harsh conclusion to life. Not for this sea slug. The creature separated its head from its body—and then dragged itself around to feed.

So, uh, how and why? Here are science’s best guesses 1/ wired.trib.al/wBg129U

This kind of body-splitting is known as autotomy—lizards, for instance, shed their tails to escape predation. Unlike lizards, though, this doesn’t appear to be a defensive strategy. And what the sacoglossan sea slug does next puts it in a class of its own 2/

A day after self-decapitation, the slug’s neck wound closes. After a week, it regenerates a heart. In less than a month, the whole body has grown back, and the disembodied slug is embodied once more 3/

Sacoglossan sea slugs are famous for their “kleptoplasty,” or the way they steal energy. In the algae that the animals eat, photosynthesis hums along in structures known as chloroplasts. Instead of digesting these, the sea slug actually incorporates them into its own tissues 4/

These chloroplasts can remain photosynthetically active for months, allowing their adoptive sea slug to draw energy from the sun. This may help keep the animal alive even after the slug’s head divorces itself from its body 5/

But why would an organism do this to itself? It may be parasites. Three of the slugs that jettisoned their bodies in the lab were infested with tiny parasitic crustaceans, and another 39 lost part of their bodies. However all of the 64 parasite-free sea slugs stayed intact 6/

It’s possible the slugs can detect when they’ve got a bad case of parasites and write the body off as a lost cause. If a sea slug is overburdened by parasites, it can’t devote energy to reproduction—its true purpose on this planet 7/

By self-decapitating, the sea slug head can survive just fine on solar power until it regrows a new digestive system and a fresh set of reproductive organs. Parasite-free, it can then go back to fulfilling its evolutionary obligation 8/ wired.trib.al/wBg129U

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