There are certainly some bizarre creatures in the world today, but none have made as many people quite as uncomfortable as the pearlfish.
While the pearlfish sounds like your average fish, it’s actually an interesting sea creature that finds shelter in the anus of the sea cucumber.
“Two strategies are observed for entering,” said University of Liege researcher Eric Parmentier of the pearlfish’s entrance to the sea cucumber’s anus. “One, head first by propelling itself with violent strokes of the tail; two, tail first by placing the head at the cloaca of the sea cucumber and moving the thin tail forward alongside its own body at the level of the lateral line. The reason for this second strategy is that the host has detected the presence of the fish and, in response, closes its anus. But the host has to breathe, so it has to dilate the anus to realize the water flow. The fish blocks the aperture and the host has to enlarge this opening more and more.”
Scientists say that the pearlfish will enter the sea cucumber’s teeth ridden anus to find shelter or to enter with another pearlfish as a place to mate. The pearlfish will either simply take up space inside the sea cucumber, or it will actually eat the sea cucumbers, well, private parts. Despite what seems like a one-way relationship, the sea cucumber does have a method of defending itself, although it doesn’t necessarily use this against the pearlfish.
“Probably the best thing that sea cucumbers are known for is evisceration, which is tossing their guts out at predators when they are harassed by them,” said Christopher Mah, a marine biologist. “So you have a crab or a fish or something and what they’ll do is literally eviscerate, just take a good chunk of their intestine that will spool out of their body and get shot out at the predator or whatever as a distraction.”
Researchers still have a hard time determining why exactly the sea cucumbers have teeth in their anus and aren’t sure whether or not that is also a defense mechanism.
In any case, it’s pretty interesting and slightly awkward to watch these creatures interact in such an unusual way.