When you think of sea slugs, their sexual processes aren't likely the first things that come to mind. But new evidence is suggesting that their sex organs might be the most interesting things about them. Not only is the red and white sea slug a hermaphrodite, but it has a disposable penis to boot.
This might sound a tad nonsensical at first, so here's an explanation that's about as nontechnical as it gets. This slug, which is about the size of a human thumb, gets rid of its penis after the sex act is complete, only to grow a new one right after. The new, "juvenile" penis was on standby already, tightly coiled inside the slug's body. This isn't just a one-time deal, either — the slug can repeat this seemingly ridiculous act at least three times. According to the research, "No other animal is known to repeatedly copulate using such ‘disposable penes’." There's a phrase you probable never thought you'd read.
If you're looking for some really steamy reading, check out how the scientists who conducted this research describe what they're doing with their lives (their parents must be so proud):
We observed 31 reciprocal copulations. After each copulation, the penes were elongated and autotomized. In a typical case, two individuals encountered and touched each other with their genital orifices and then projected their copulatory apparatus after they separately crawled on the bottom and side of an experimental tank. After two individuals touched with the right side of their bodies, and adjusted the tip of the projected genitalia of the other, each inserted its penis into the partner's vagina and started copulation. After tens of seconds to a few minutes from the beginning of copulation, they pushed away the partner using the buccal bulb and separated with their penes stretched and elongated [see Fig. 1a, b in the diagram above]. When both individuals advanced further, one individual removed its own penis from the partner's vagina. After a few minutes, the other individual also removed its penis and their copulation ended. After copulation, both individuals crawled with their elongated penes remaining outside the body. Finally, they autotomized and discarded their penes [See Fig. 1c].
Here's the real clincher: Both slugs are performing the male and female functions simultaneously during sex, which sounds like a workout. It needs about 24 hours to regrow its poor little discarded ding-dong, so no sex marathons for the red and white sea slug. The act of copulation can last from seconds to minutes, which sounds an awful lot like someone I know (rimshot!).
Scientists described the slug's penis as a "thread-like organ" that extends from its side. The penis-thread was found to be covered in tiny spines (see Fig. 1e above) believed to help remove sperm from previous partners. The spines understandably make it pretty hard to, er, remove the penis after sex, which might help explain why the thing just falls off.
So remember guys, if you're having a really bad day, just be glad you don't have to regrow your manhood every time you get your rocks off.