Barnacles’ Penises Are Eight Times as Long as Their Bodies

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 order to find receptive partners in the tumult of rough ocean waves. The latest video from KQED’s Deep Look YouTube channel includes even more fun facts about their sex life and notable reproductive organ.

We also learned from WIRED that the length and girth of barnacle penises varies depending on the literal motion of the ocean. They have shorter and thicker penises in rough intertidal areas with lots of waves. This helps them control it in all the chaos. Those that live in calmer water have longer, thinner penises to reach and mate with as many partners as possible.

The length and thickness of barnacle penises even changed when researchers moved them from one environment to the other. Yes, there are scientists out there measuring and recording barnacle penis length.

Graphic showing the inside of a barnacle, its head fused to the rock and its back legs out in the ocean
Deep Look

You may have seen barnacles at tidepools, piers, or attached to a boat. When out of the water, they seal tightly shut. But once underwater, feathery appendages stick out and catch passing food particles. It’s actually their face that fuses and their butt and legs that are in the water. We learned about this back during Invertebutt Week on science Twitter.

Barnacles are hermaphrodites, meaning each individual has both male and female reproductive organs. They act as one or the other and cannot fertilize their own eggs.

A barnacle extends its long penis to fertilize the eggs of another

The barnacle’s prodigious member is only the latest deep dive into cool critter videos from Deep Look. Others include sea stars galloping and hydra regrowing limbs.

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth. 

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