An invasive sea creature with a disappearing anus and a penchant for cannabalizing its own young may have yet another trick up its sleeve. When life is going badly for the sea walnut, it will shrink and take on the shape of its larval form, and stay that way until things are looking up again, according to Norwegian researchers. "We found that under certain conditions, these animals can basically go back in their life stage," Pawel Burkhardt, an evolutionary biologist at the University of Bergen in Norway, told As It Happens guest host Susan Bonner.
"That was completely unknown for that group of species. It was a wonderful, wonderful finding." The study's authors characterize this as "reverse development" — or, more simply, aging backwards.
If they are correct, the sea walnut joins an elite group of organisms known to have this extremely rare ability, alongside Turritopsis dohrnii , a.k.a.
, the immortal jellyfish , and Echinococcus granulosus , a type of parasitic tapeworm . But some scientists are critical of the study's conclusions, saying the sea walnut's ability to change its shape and size in response to external stimuli is already well-documented, and it doesn't mean they can develop in reverse. The findings were published this week in the pre-print journal BioRxiv and have not yet been peer-reviewed.
Responding to stress Mnemiopsis leidyi , also known as a sea walnut or a warty comb jelly, is not a jellyfish, but rather a type of transparent, lobed marine invertebrate.