A New Anus for Every Poo?
What if body parts only appeared when you needed them? That is what the warty comb jelly has: its anus only appears when it needs to poo. After that it disappears again.
When you look at a warty comb jelly it is not immediately clear which is the top and which is the bottom (tip: it usually swims and rests with its mouth upwards). Even when you look at it more carefully under a microscope there is still a problem: the warty comb jelly does not always have an anus. Yes, you read that right: this jellyfish has an anus that comes and goes.
When the need is greatest
This "disappearing anus trick" was discovered in 2019 by Sidney Tamm of the Marine Biological Laboratory. Prior to this, little was known about the anus of these jellyfish. The creature has two structures at the rear end called the large anal lobes. When the jellyfish needs to poo, one of these swells more than the other. It has now been found that it is only then that the anus appears, on the more swollen side.
If you look under the microscope, there is no hole present before defecation begins. Internally, everything is there: the warty comb jelly has a mouth, stomach and intestines, and its food goes all the way through. The intestine only fuses with the outer layer of cells to create an opening when needed: this forms the anus. It remains until the jellyfish has done its business. After that, the opening closes again.
Every 10 minutes
Creating an anus in this way doesn't sound like a fun experience. So you might think warty comb jellies would keep their "toilet trips" to a minimum. Nothing could be further from the truth. The anus of a large adult warty comb jelly appears and disappears about once every hour. Warty comb jelly larvae even form a new anus every 10 minutes.
These creatures are (so far) the only ones that have been found to have a disappearing anus like this. Further research into their "intermittent" anus may help to explain how permanent anuses evolved in other animals, including our own.