Male barnacles have the largest penis proportional to its body size in the animal kingdom. It can reach up to 50 times the length of the barnacles’ body. It reaches out of the shell and transfers its sperm to a female neighbor. After fertilization, the female barnacle broods its eggs until they hatch as a minute nauplius larva which swims until it transforms to another larval stage called a cypris that then settles head-down on a suitable surface.

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