If you’ve ever tried to remove a barnacle from a boat hull or piling, you learned they don’t go easily. You’re lucky if they go at all. Barnacles cling to ships, rocks and even to the skin of whales.

Barnacles have the longest penis of any animal, relative to body size. Adults fuse onto one spot, so this is a necessary adaptation to reach eggs to fertilize. Their penises also taste and smell in ...