Relax: none of those things on top are dongs (I think).
This is the Chromodoris reticulata species of sea slug. While it's generally accepted that all sea slugs have unusual sex practices, this species is particularly interesting to scientists because it can shed, regrow, and reuse its penis. "Now would be a good time for a John and Lorena Bobbit joke." Please, there's never a good time for a John and Lorena Bobbit joke.
"The penis from one fits into the female opening of the other one, and the penis from that one fits into the female opening of the first one, if you see what I mean.
"They are both donating sperm to the other one."
Closer examination of the animals' anatomy revealed that the sea slugs had a large part of their penis coiled up in a spiral inside their bodies, which they would then use to replenish their missing part.
Not gonna lie, that was freakier than I was expecting. Still, I wish I had a large part of my penis curled up inside my body like a sea slug. I would uncoil that thing like a garden hose and-- "And what, GW?" Jump rope party!
♫ Miss Mary Mack, Mack, Mack
all dressed in black, black, black
With silver buttons, buttons, buttons
All down her back, back, back ♫
*trips over penis-rope, eats sidewalk*
Thanks to Rev Dr Dom, scitastic, fat piggie and Pogonophile, who heard that regrown sea slug penises, like Starfish tentacles and lizard tails, are never as pretty as the original.