Heads up: There’s always room for growth.

Japanese sea slugs will no doubt become the envy of superhero fans — and perhaps certain 1700s French nobles — after showcasing a bizarre penchant for regenerating their own heads.

“We think that this is the most extreme case of autotomy,” said Yoichi Yusa, an aquatic ecology professor at Nara Women’s University. She spearheaded the slimy new study published Monday in Current Biology.

The doctoral student was reportedly examining the oceanic invertebrates in the lab when several of the slugs inexplicably removed their own noggins, the AP reported. They then spontaneously regrew them, like the head-regenerating alien from “Men in Black.”

In order to prove that the regeneration ritual wasn’t a fluke, Yucha sliced the heads off 16 sea slugs. Six of the subjects initiated the regrowth process, with three successfully sprouting a new dome. Of the latter trio, one slug even lost and regenerated its body twice, bringing new meaning to refusing to quit while you’re a head.

The scientists found the ability particularly miraculous because while some animals can sprout new legs and other appendages, “no other animals could shed their whole body,” she said. Prior research had assumed that the relatively big slugs — which can attain 16 inches in length — couldn’t survive without a heart.

Yucha and her team have deduced that the hydra-like ability is rooted in the slimers’ habit of photosynthesizing food from sunlight just like a plant. Post-beheading, their tiny heads would even turn green and harness energy from oxygen and sunlight.

Noodle-renewal seem like a neat party trick on its face, but scientists think the mechanism helps ward off parasites.

Most importantly, humans may be able to apply this regenerative superpower to modern medicine.

“It is of course a wonder of nature, but understanding the underlying molecular mechanisms involved could help us to understand how our cells and tissues can be used to repair damage,” said Nicholas Curtis of Ave Maria University in Florida, who wasn’t part of the research.