Mating barnacles from Casey Dunn on Vimeo.

Barnacles, those marine crestaceans that attach themselves to rocks, mate by extending their long penis outward and searching for other nearby barnacles. According to Creature Cast, barnacles have the longest penis length relative to its size of any living thing. So next time you see a rock covered in barnacles, just remember that that same rock is also covered in lots of long penises. [via]