[MUSIC PLAYING] NARRATOR: Behold, the California floater mussel, a freshwater bivalve with the soul of a nomad.

Unlike their saltwater cousins that clamp onto rocks, they drag themselves across riverbeds and sandy lake bottoms.

They use what looks like a wide, gooey tongue, but it's actually called a foot.

When they need to find food or deeper, cooler waters, they can move a few meters in a matter of hours.

That's speedy for a mussel.

Their wanderlust starts early in life.

This mussel mom is filled with eggs fertilized by a nearby male.

Within the safety of her rugged shell, the eggs move from the gonads into the gills.

Then they develop into mussel larvae called glochidia.

When it's time for these young mussels to strike out on their own, they make their exit.

Mom launches them by the tens of thousands into the wide, watery wilderness... along with some of her own waste.

Good luck.

Roughly the size of a grain of sand, the glochidia look like translucent butterflies.

But they're really just teeny tiny mussels fluttering through the open water.

Each one dangles an almost invisible thread that helps them float and latch onto what's around them.

Some drift freely, while others get tangled up, forming sticky trains with their brothers and sisters.

They're looking for a ride.

This three-spined stickleback is the perfect vehicle.

The luckiest glochidia clamp onto a fin or gill using hooks on the tips of their tiny shells.

These little hitchhikers tour the lake for one or two weeks, absorbing nutrients from their living ride.

The glochidia grow into juveniles during their travels.

When their transformation is complete and their tiny foot emerges, they drop to the bottom of the lake-- all on their own for the first time.

Their shell is still soft, so they quickly dig into the lake bed to hide from predators, like this polychaete worm.

It's dangerous down there.

Those who do grow up stay active behind those closed shells.

They pull in water through one opening.

They filter it, keeping the food and oxygen.

Then they spit out the waste through the other opening.

Studies show that lots of mussels can dramatically improve water quality by filtering out algae and harmful bacteria.

Plus they help concentrate nutrients on lake bottoms and riverbeds for other aquatic plants and animals.

Scientists are re-establishing mussels like the California floater in their native habitats in North America, where they were once plentiful.

California floater mussels are more than just wanderers; they grow up to be hardworking neighbors in their aquatic communities, making the water cleaner for all the life that depends on it.

Hi, it's Laura.

Want to keep exploring underwater worlds with Deep Look?

Here's a playlist of our favorite aquatic episodes.

But if you like your water freezing cold, take an expedition to Earth's most remote laboratory in Antarctic Extremes from our friends at NOVA.

You can find it on Terra, PBS Digital Studio's new YouTube science channel.

Link is in the description.

Tell 'em Deep Look sent you.