The barnacle is a type of arthropod that can be found clinging to surfaces - from rocks to boats - in marine waters throughout the world. They're common, but not as mundane as you might think: They have the animal kingdom's largest penis (in proportion to their body size).
The blue whale actually has the largest penis, measuring in at a whopping ten feet in length and twelve inches (...AROUND) in diameter. In proportion to body size, however, barnacle trumps all. The penis of a male barnacle reaches around eight to nine times its body size.
Why would nature bestow such a lengthy penis for the humble barnacle? Barnacles live a stationary life, basically cementing themselves to surfaces after a brief mobile stint sometime after birth.
With such a long penis, they are able to poke around for neighbouring female barnacles to spread their seed.
Research from 2008 suggests that barnacles have a variable penis size. Those living in gentle waters have longer, thinner penises, whereas barnacles living in rougher waters have shorter, thicker penises.