In absolute terms, the blue whale has the largest penis of any animal—a huge mobile appendage that can reach 10 feet in length. But the blue whale itself is enormous. If you take body size into account, the animal kingdom’s champion penis belongs to a much smaller creature, and one that often lives on the faces of whales. It’s the barnacle.

Barnacles are found wherever hard surfaces meet seawater, including boats, moorings and whale heads. They look like little rocks, but they’re actually crustaceans—close relatives of crabs and shrimp. While their relatives walk about, barnacles affix themselves to a surface, and filter food from the water with protruding paddling legs. This stationary life poses a problem when it comes to