Forget sea-slugs with detachable pensises: the Siphopteron species 1, recently discovered by the University of Tubigen's Rolanda Lange, has the most awesomely weird sex-life of any sea-slug heretofore known to sea-slug perverts.
The 2-3mm-long slugs are fork-penised hermaphrodites, and during sex, they interpenetrate each other -- each slug puts one tip in the other's female sex organ; and uses the other tip to skewer its partner's forehead and pump prostate fluid directly into its head during a sex-act that lasts for 40 mind-blowing minutes.
This process is known as "cephalo-traumatic secretion transfer."
Every individual is a hermaphrodite with both male and female genitals. When they have sex, they can simultaneously penetrate each other, with penises that extend to their whole body length. “They are relatively well-endowed, says Lange.
The penises are also forked. One branch ends in a cone-shaped structure called the penile bulb, which is ringed by small spines. It goes inside the partner’s female genital opening, and delivers sperm. The other branch ends in a fiendish spine called the penile stylet. It stabs straight into the partner’s forehead, and pumps fluid from the prostate gland. So, during sex, each slug gets a dose of sperm in the usual place, and an injection of prostate fluid just above its eyes. This goes on for just over 40 minutes.
“You may imagine I was quite excited and surprised to find out they reciprocally injected into their partners’ head!” says Lange.
These Sea Slugs Penetrate Each Other In The Head During Sex [Ed Yong/National Geographic] (via JWZ)