A lot of species do some wild sex stuff. The purple stone crab is no exception: Females have seminal receptacles, a special organ that just holds and stores sperm for later.
Purple stone crab (Photo; Nahuel Farias/Flickr)
Researchers studying the purple stone crab's female parts wanted to get a better look at these sperm holders. But they're not just any sperm-holders. The simple sacs are full of mystery. And they can store a load of sperm.
The researchers collected adult specimens during three scuba diving trips in the Argentinian Mar del Plata harbour, as well as on the harbour's rocky shores. They dissected and photographed the crabs' reproductive systems and observed them with a microscope.
The receptacles start as long, thin sacs filled with fluid before maturation. But when the crabs mature and start boning, the sacs fill up a lot. Part of the sac "occupies much of the internal cavity of the body," the authors write in the paper published recently in the Journal of Morphology, "closely resembling the finger of a latex glove." Euuunnngghhh.
And when the researchers cut into the little glove finger, they found different masses of sperm that they could easily pull apart. God, I have a picture of these things but don't have permission to share them. They're horrible. Think of a crab you'd eat. Now pretend it has two latex glove fingers wrapped on either side of its belly. Now imagine the sacs filled with wads of compacted sperm. That is what I am currently sparing you from seeing. But just know that I really want to show it to you.
The purple stone crab isn't the only species with seminal receptacles, but theirs is actually simpler than the ones in spider crabs which have extra pieces of muscle to save some sperm for later. But the researchers highlighted that the purple stone crab seminal receptacles are huge, probably the largest (relative to their size) of any described crab species.
But the weirdest part: The volume of these sperm ducts aren't correlated with the amount of sperm the males deliver. That means the receptacles probably hold sperm from several males, and they're built so the newest sperm does the fertilising first.
These crabs' female reproductive tracts are still a mystery, though. The females don't seem to save all that sperm between broods, for example. And the researchers saw hints that the females have other control over mating, like muscles to resist males trying to mate when the female doesn't want to.
Anyway, awesome, gross, happy weekend.