If you’re not familiar with comb jellies, take a moment to watch the video above, a National Geographic exposé on a unique sea creature that few of us (not in the marine science fields) often consider. They’re beautiful, right? But that’s not the most impressive thing about these sea creatures, because scientists have just discovered that they have anuses. That’s right, the creatures you see in the video (and at your local aquarium) have buttholes they can use to excrete digested food right out into the ocean.
Why is this news, you ask? That’s a very good question with a very important answer: for years, researchers, people who study jelly combs on a regular basis, thought that the organisms only had one hole for eating and excreting (don’t think about it; there’s a reason that Science is calling “the butthole” one of the “most important evolutionary adaptations in the last 540 million years”) and couldn’t do one while doing the other. A new video, however, has proven them wrong, and the science world is in an uproar.
Science reports that history was made on March 15, when new video evidence by evolutionary biologist William Browne was shown exhibiting comb jellies eating through their mouth and excreting through another area, putting accepted theories that the animals didn’t have a through-gut (meaning that food didn’t come out the other end of their digestive system) into serious jeopardy.
Browne’s videos elicited gasps from the audience because comb jellies, whose lineage evolved long before other animals with through-guts, had been thought to eat and excrete through a single hole leading to a saclike gut. In 1880, the German zoologist Carl Chun suggested a pair of tiny pores opposite the comb jelly mouth might secrete some substance, but he also confirmed that the animals defecate through their mouths. In 1997, biologists again observed indigestible matter exiting the comb jelly mouth—not the mysterious pores.
And then this happened:
Browne, however, used a sophisticated video setup to continuously monitor two species that he keeps in captivity, Mnemiopsis leidyi and Pleurobrachia bachei. The movies he played at Ctenopolooza capture the creatures as they ingest tiny crustaceans and zebrafish genetically engineered to glow red with fluorescent protein. Because comb jellies are translucent, the prey can be seen as it circulates through a network of canals lacing the jellies’ bodies. Fast-forward, and 2 to 3 hours later, indigestible particles exit through the pores on the rear end. Browne also presented a close-up image of the pores, highlighting a ring of muscles surrounding each one. “This is a sphincterlike hole,” he told the audience.
Important scientific findings aside, I would like to know how to get an invite to the next conference, because nothing has disappointed me more than knowing that I missed a presentation which featured the phrase “this is a sphincterlike hole” followed by audible gasps.
But here’s why that sphincterlike hole is so important: Not only does it suggest that biologists may have not been watching comb jellies closely enough to determine how their digestive systems worked (the new theory is that they excrete out of their mouth when they’ve overfed or “eat the wrong thing,” meaning that they, too, are gluttons) (comb jellies, they’re just like us!), but it also suggests that the evolutionary process as we currently see it may not be as straightforward as once thought. Comb jellies evolved before other sea animals that have only one hole for both eating and defecating, so how’d they do it?
One possibility is that the comb jellies evolved through-guts and anuslike pores on their own, independent of all other animals, over hundreds of millions of years. Alternatively, a through-gut and exit hole may have evolved once in an ancient animal ancestor, and subsequently became lost in anemones, jellyfish, and sponges. Perhaps if you’re an anemone or a sponge stuck to a rock, suggests Matsumoto, it’s better to push waste back into the current rather than below.
Yes, I know we’re talking about animal buttholes here, but that’s actually pretty cool. And if these animals were able to evolve independently, what else does that mean about evolution and digestive efficiency?