Finding a date is hard enough in San Francisco.

But it’s especially tricky when you’re  stuck to a rock in the middle of the bay.

Still, acorn barnacles don’t get discouraged.

These crusty little animals actually  have a pretty wild sex life.

At low tide each one is sealed up inside its   own miniature fortress – shielded  by a ring of armored plates.

The two central plates press  together to form a water-tight seal   so they don’t dry out in the open air.

They’re ready and waiting for the tide  to rise so they can get down to business.

But first they need to freshen up a bit.

The barnacle unfurls eight pairs of  delicate feathery legs called cirri,   which they use to absorb oxygen from the water.

The legs filter out plankton and  debris churned up by the waves,   bringing the catch inside to the mouth They may not look like it from the  outside, but beneath their shell,   it's easier to see that barnacles are  crustaceans related to crabs and shrimp.

After a nice meal, it’s ready for some action.

The little barnacle lets loose the longest  penis of any animal – relative to its body   size of course – stretching up to eight  times the length of the barnacle itself.

And this penis has skills.

It can taste and smell.

And the tip can feel around, probing to  see which neighbors have ripe eggs inside.

When it finds what it’s looking for the  barnacle delivers sperm to fertilize the eggs.

Barnacles aren’t exactly prudes.

Pretty much everyone is fair play.

Because they’re all hermaphrodites,  simultaneously male and female.

Sometimes it’s one-on-one, sometimes more.

Barnacles are nurturing parents, too.

They hold on to their fertilized eggs  and protect them until they hatch.

These cuties are their baby larvae called nauplii.

This is the young barnacles’ chance for adventure.

They roam the sea searching for food and growing.

If they survive long enough the  barnacle larvae mature into cyprids.

At this stage the barnacle doesn’t eat.

The cyprid’s only mission is to find the  ideal spot to glom onto before it starves.

Having survived the trials of  youth, the barnacle settles in.

Now it’s time to get to know the neighbors.