Those aren’t cornflakes.

This rock is absolutely covered with  tiny marine flatworms, called acoels.

They're not just an animal.

They're also kind of a plant.

And they’re practically immortal.

They use simple eyes called ocelli to seek out  the sunniest spots on tropical coral reefs.

Where they spread themselves  out like beach blankets.

But they don’t just lay around sunbathing all day.

Acoels are also skilled hunters.

They catch prey by engulfing them with their  body and jamming them into their mouth.

You can see their meal trying in vain to escape.

Also, they don’t have a butt.

Their poop just goes right  back out through their mouth.

So you wouldn’t want to kiss one.

They aren’t just hunters.

These acoels are gardeners, too.

See those green dots?

Those are algae.

And those reddish cells  belong to the acoel itself.

When the sun hits our flatworm friend, the algae  inside produce sugars through photosynthesis.

Researchers think they share  those sugars with their host.

In return, the acoel provides its, um, waste,  which is like fertilizer for the algae.

And the acoel protects its house guests.

Researchers think the acoels pack  toxic chemicals in those reddish cells.

So predators tend to leave them alone.

Without its algae, the acoel would eventually  die, even if it had plenty of prey to eat.

Scientists call a creature like this a holobiont,   a single being made up of two or  more completely different species.

In this case, a solar-powered predator.

But that’s not even the weirdest thing about them.

Researchers at Stanford University and  the University of San Francisco are   studying acoels, because of how they regenerate.

And to do that … It’ll be OK, I promise.

You’d think getting cut in  half would be a bad thing,   but within minutes, the  wounded front half seals up.

In a couple days, it’ll have a whole new tail.

And the back side?

It doesn’t just make a new head.

It makes two!

But it’s hard to share one body with two heads.

So each half eventually pulls away from the other.

Where there was once one  acoel, now there are three!

What seemed like a moment of  doom was actually one of rebirth.

But they don’t need the researcher’s scalpel;   acoels can drop their tale and  clone themselves on their own.

The acoel and its algae can multiply themselves   like this over and over indefinitely,  making them functionally immortal.

Acoels can do this because they’re  packed with stem cells which morph   into any body part the acoel needs to regrow.

And since they can’t hunt  until they grow new heads,   they’re extra reliant on the  energy they get from their algae.

In these desperate times, the  acoels even eat some of their algae.

Sorry!

Every relationship has its challenges.

But the acoel and its algae have a deal: By taking advantage of each one’s abilities,  they’re greater than the sum of their parts.