Barnacles are stuck to rocks, which could make it tricky to get close enough to a partner to mate. They have solved this problem by evolving the longest penis relative to their body size of any animal. In this video the penises of several barnacles are probing the neighborhood for mates. The penis is re-grown each mating season. Check out creaturecast.org for more.
This video was filmed by Stefan Siebert. It is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Thanks to David Rand.