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> Just a head makes a whole new body:
> 
> https://www.sciencenews.org/article/sea-slug-detached-head-crawl-regenerate-grow-new-body
> 
> "Heads of young Elysia cf. marginata sea slugs can pull themselves free from their bodies and just keep crawling around while growing a new body, report ecologists at Nara Women’s University in Japan. Within a few hours, some separated heads start nibbling on algae again, Sayaka Mitoh and Yoichi Yusa report March 8 in Current Biology. And within about 20 days, a third of the young sea slugs they watched had grown their bodies back, heart and all.
> 
> ***
> 
> "The head of a sea slug can take several hours to rip itself loose from its body, so Mitoh and Yusa doubt that de-heading helps when predators attack. Instead, a detachable body could give the sea slug a drastic, but effective, way of dealing with parasites. In a batch of wild-caught E. atroviridis sea slugs, the few that ditched their bodies were parasitized by copepods. So were those that just lost pieces of their body, some of which also regrew.
> 
> "On close inspection, the researchers found that sea slugs have a slight groove looped on the back of the head region that seems to work as a break-here zone. The bodies left behind can still move on their own for days or even months. An abandoned body, however, doesn’t regrow its head. The leaf-shaped remnant instead turns pale and weak and eventually dies.
> 
> ***
> 
> "What might help Elysia slugs manage such extreme regrowth is their ability to steal the tiny green sunlight-trapping energy factories called chloroplasts from plants, the researchers muse. Very young slugs don’t have any chloroplasts. “They need to pierce the cell walls of sea algae and sip the contents,” Yusa says. The grazing slugs can keep the chloroplasts alive for weeks or months.
> 
> "Biologists debate what the stolen chloroplasts do for their kidnappers besides provide a pretty, green tinge.  Yusa, however, has linked the looted chloroplasts to such consequential matters as improved reproduction. If chloroplasts are more than cosmetic, maybe that energy boost is just what a severed head needs to get (more than) ahead."
> 
> Comment: What this means is ordinary DNA in the slug has all the information need to reproduce a new slug, not a special reproductive set of cells. Snapping up necessary tools from other organisms is common. That is how we got our mitochondria.