Yes, that long thing is a barnacle penis mating with its neighbor (Image Credit: Sue Scott, MarLIN)

Barnacles, those crustaceans that stick themselves to the bottom of boats (much to the consternation of sailors everywhere), are stuck in one position all their lives.

So, how do they mate? The solution, turns out, is brilliantly simple: the barnacle has an inflatable penis that is up to 50 times as long as its body. In fact, it has the longest penis in the animal kingdom, relative to body length!