Barnacles are an inevitability in the ocean. Ships are covered in them, rocks are covered in them, even animals are covered in them — they're everywhere. But, while you might be familiar with what barnacles look like on the outside, you probably haven't ever seen them move. Yes, barnacles are living, breathing (sort of) animals, and seeing live barnacles use their feathery legs to eat is, in a word, freaky.
The most common barnacle is the acorn barnacle. They're the little hard, white things that stick to driftwood and rocks and the hulls of boats.
You can even see them on whales.
Because most people see barnacles in the air (rather than underwater), we're not really seeing the full animal. According to Oceana, barnacle shells close when they're exposed to light or air "to prevent them from drying out." But, the National Ocean Service reports that things really liven up when they're submerged.
Barnacles are enclosed in six hard plates surrounding them, and four more plates that make a sort of door on top. It's this so-called door that opens and closes based on the water.
"When the tide goes out, the barnacle closes up shop to conserve moisture. As the tide comes in, a muscle opens the door so the feathery cirri can sift for food," the National Ocean Service says.
What are feathery cirri, you ask? Just these little whiskery feet.
These cirri are where the barnacle gets its scientific name "cirripedia," which means "curl-footed" in Latin.
You can see why they got this moniker:
The Monterey Bay Aquarium reports that these little legs help the barnacle eat, sweeping through the water looking for plankton and small debris to feed on. The legs also help the barnacles breathe.
They don't have gills or lungs. Instead, as the Monterey Bay Aquarium notes, "Gases are exchanged through cirri ... and body walls." The Marine Education Society of Australasia also reports that these legs are why the barnacles' main sense is touch.
Their fine leg hairs are super sensitive.
It makes sense that barnacles have far-reaching legs (and penises — the longest, relative to body size of any animal) because the rest of them has to stay put. Once barnacles attach themselves to something, they're pretty much there for life, barring human desire to remove them (and even then, they hang on good).
They attach themselves by secreting "a fast-curing cement" that's so strong it's being studied for commercial use.
So their legs do the job of searching the water for food, and their penises extend from their shells and probe into other barnacle shells for reproductive purposes. The rest of them stays where they are.
They're so difficult to remove that some seamen call them "crusty foulers," according to the National Ocean Service.
But, what's not foul about them are their silly feathery legs rapidly combing the water for nutrients.
Mostly it's just so fascinating to watch a sedentary animal work so hard.