Answer by Diana Crețu:
The oceans house a very strange little worm, called Osedax.
It is not strange because it feeds exclusively on dead whale bones (OK, a little because of that, too).
It is however extremely strange for a different reason.
When scientists first discovered it they were dumbfounded because they saw the worm very eager to spawn lots and lots of offspring all over the place, but… the worm was female, and only female, and there were no males in sight.
Since the scientists weren't yet ready to believe in immaculate worm conception, they decided that there had to be a male somewhere, somehow. So they started looking for him (with private investigators following the female around and all). But still nothing. The female was sitting at home, lazily munchin' away on those dead whale bones, and spawning new wormsters every now and then.
That went on for a while, until you know, just like when you really can't find your keys and you start looking for them in the freezer or in the soup, they started looking in the most unusual places. And that's when they looked inside the female.
And guess what. They found a whole gentlemen's club in there. With a bunch of microscopic males talking politics and smoking cigars while rubbing their private parts on the inside of the female and what not.
Oh, nature, you!
Much later edit:
No, no, no, wait!
I thought I was giving you the strangest one I knew, but I was not even close.
I had completely forgotten about the tongue-eating louse! And, believe me, it's scarier than its name predicts.
Let's do a quick exercise. You over there, start being aware of your own tongue. Go ahead, move it around your mouth, roll it, touch your teeth, lick your lips and so on.
Now imagine your tongue has a different texture. It's maybe a little stiffer too. And it feels ticklish underneath, especially when you move it around. The strange sensation sends you to a mirror, you open your mouth aaand… you have some sort of a roach-looking creature for a tongue! Take that Mr. Kafka!
Now, before you start running around the place screaming, don't. We humans are safe. Only some fishes drew the zombie-tongue card, and I'm hoping that's where evolution comes to a stop.
This parasite (crustacean as well) enters the fish through the gills, then hangs on to the base of the fish's tongue. Then starts feasting on it. When the tongue is gone, they're like "Oh hey, look, space", and they move into the empty place where the tongue once was, and proceed to become the fish's new tongue. Fancy that!
I'd add pictures, but some of you have eaten, and all of you have Google. Enjoy!