Fans of '90s alternative music may recall King Missile's big single, "Detachable Penis." While the song may have been silly, it turns out than in the animal world, the idea isn't all that bizarre—at least not to the sea slug Chromodoris reticulata.
This odd creature is hermaphroditic, which is pretty common among sea slugs. What isn't all that common, though, is what this particular slug does with its member after copulation. During mating, the two slugs will insert their penises into one another's vaginas. After the slugs go their separate ways, their penises will then sever and float away—but each slug's penis is actually longer than it appears, and the 3 centimeter portion that detaches is just one of three segments. The other two, coiled inside of the slug, have "cells ... different from those in the uncoiled part, which suggests that these replacements must undergo some changes before they can be deployed," Ed Yong writes at National Geographic. The next segment readies itself within 24 hours (researchers have even observed some individuals growing and shedding their appendages over and over in order to copulate three times in three days). When all three segments are spent, the slugs' penises eventually grow back, although no one is sure how long that process takes.
While other animals have been known to shed their penises after mating, so far the slug is the only one that seems to immediately grow the part back, and researchers still wonder at the evolutionary benefit this offers the animals.
Primary photo courtesy of Flickr user Stephen Childs.