Even in the utterly dry language of science, there is no way to describe the mating behavior of the sea slug Chromodoris reticulata as anything other than bizarre. The creature, native to the Pacific Ocean, engages in simultaneous hermaphroditic mating—that is, each slug has both a penis and a vagina, and when mating, both members of a couple inserts their penises into the other’s vagina at the same time—but that’s not nearly the strangest aspect of their reproduction efforts.
As discovered by a group of Japanese scientists and revealed today in the journal Biology Letters, it’s what C. reticulata does after sex that is particularly unexpected—and previously unknown in the animal kingdom. After copulating for about 10 minutes, each slug discards its penis and immediately begins growing a new one, which is ready for use within 24 hours. - Continue reading atSmithsonian.com.