What creature has the largest penis in proportion to its size?

Barnacles have the biggest penis-to-body size ratio, with genitalia nearly eight-times their total body length. Barnacles are stuck in place for life, so they use their super-long penises to reach other nearby crustaceans, blindly depositing sperm inside their neighbors. Like flatworms, barnacles are hermaphrodites that can fertilize others, be fertilized or both.