Look at this animal. Just look at it. It’s glorious.
Found almost a kilometer below the surface of the ocean, this hazelnut-sized marine worm lives, breathes, and floats around looking exactly like a tiny, perfectly plump rear end.
The species was discovered floating freely through the ocean in 2006 by a remotely operated vehicle off the coast of California. This little submerged research robot scooped up a handful of pigbutt worms, and Karen Osborn, a marine biologist from the Monterey Bay Aquarium Research Institute, got to analyze and name them. So she called them Chaetopterus pugaporcinus, which in Latin literally means “worm that looks like a pig’s rump”.
This otherworldly purplish bubble creature with its pink, puckered mouth is unlike any other species of worm ever found. In trying to figure out what the pigbutt worm’s deal is, Osborn compared her specimens to several other known species of marine worm. She was able to find some physical similarities between her pigbutt worms and the larvae – or young – of a large family of marine worms worms called Chaetopteridae, so perhaps, she thought, her pigbutt worms were in their juvenile form?
But that would be weird, she reported in a 2007 edition of the Biological Bulletin, because at 10 times larger than any known chaetopterid larvae, her pigbutt worms were already relatively enormous.
So if they were too large to be babies, the only other option was that Osborn’s pigbutt worms were in their adult form. But now their free-floating lifestyle was a problem, Osborn said, because it was completely at odds with what all other adult marine worms are known to do when they grow up.
When other marine worms reach adulthood, they quit floating aimlessly through the open ocean and migrate to the seafloor. Their bodies start to elongate, which allows them to live in the safety of the vertical tubes they’ve built inside tiny, underground tunnels. Here they can spend their days catching little bits of food with the mucus nets they suspend over the top of their tubes.
Pigbutt worms, on the other hand, don’t appear to hide in tubes. They were found drifting freely up to 1,200 metres below the surface of the ocean, using their little mucus-filled mouths to gather microscopic food as they went.
So in the context of what we know about marine worms, pigbutt worms don’t make a whole lot of sense. But Osborn suspects what might have happened to the species is that as it evolved over many thousands of years, the larvae were for some reason unable to anchor themselves to the seafloor. This would have halted the development of the species’ elongated adult form, and instead the pigbutt worm ended up with a flattened middle segment, and two inflated outer segments. Not skinny enough to fit inside underground tubes like other marine worms, the pigbutt worm was forced to retain its free-floating lifestyle for good.
I guess if you’re going to be different, you might as well be a pigbutt worm.
—Bec Crew / @BecCrew