Penis fencing

This is fun, to my inner twelve-year-old, 'cause I get to pretend it's just science stuff and all, while I get to say "penis" a lot. Penis. Giggle. Gets me a good Google rank as well.

These flatworms (Wikipedia, new window) are hermaphrodites. Mating involves a violent battle over who puts what into whom - there's an advantage that goes to the individual who inseminates the other and is spared the burden of bearing the offspring.

About two minutes.

From the midsection of each flatworm double daggers protrude, Each dagger is actually a penis.

The first one that can make a successful jab delivers its sperm.

A bout of this violent sex can last up to an hour, and leave gaping holes in the body the loser.

This is Pseudobiceros hancockanus.
Really. Read that again.

Giggle.

From PBS here.