- [Mark] Tonight we are on the hunt

for something truly bizarre.

As I hope to encounter the aliens of the reef.

(drums pounding)

(animal roaring)

(bird calling)

Incredibly, humans have only explored

around 5% of the world's oceans.

And with so many places left to look,

and marine life yet to be encountered,

every single dive presents the opportunity

to see something new and truly out of this world.

(beeps)

And at night, the odds of witnessing

other-worldly cephalopods goes up at least tenfold.

So with that in mind the crew and I

are setting up our gear and bringing

our dive lights with us on a mission to find

the most alien-like creatures on our planet.

(mysterious music)

My eyes struggle to scan the empty space around me

for a glimpse of anything.

But just like that, we have our first visitor.

(dynamic music)

Drawn in by my camera lights,

I find these Caribbean reef squids stunning

and very interesting to observe.

Oddly enough it actually might be

as equally as interested in me.

They can be quite the characters

and are extremely intelligent.

It's mesmerizing how its bright coloration

and translucent skin glimmer

as it flutters its fins against the dark inky water.

Isn't it incredible how it can remain

in perfect position with so little effort?

Closely related to octopus and cuttlefish,

these torpedo-shaped cephalopods have ten appendages

set in front of two very large complex eyes.

And while Caribbean reef squid are normally

social creatures, seeing one all alone isn't that uncommon.

Wow, they really are something.

What an interesting creature to kick off tonight's dive.

(dynamic music)

I learned long ago that a strong sense of curiosity

can be the best defense against any fear.

Curiosity, like our dive lights,

can illuminate our minds to focus on

what we can see instead of imagining

what figments may exist beyond the shadows.

And in this world almost anything my light touches

brings my curiosity to a boil.

(whooshes)

The weightlessness of diving,

combined with this foreign landscape,

feels like nothing less than a space odyssey.

So in the spirit of worlds beyond our imagination

tonight we are on the hunt for something truly bizarre.

(dramatic music)

The walls of the reef are really impressive.

Covered in brightly colored sponges

that tower up at steep angles,

giving way to flatter coral beds.

(crunches)

Wait, what was that?

I heard a crunch.

Like some sort of popping sound.

Whoa, that's what I heard.

That grunt just smashed that smaller--

Oh, and look at that!

There's an octopus.

Did you see it before it changed color?

That's a Caribbean reef octopus.

And a big one too.

Now they can be extremely difficult to find,

but once spotted will flicker with color.

And these color displays are remarkable.

It's both attempting to blend in with the reef

to camouflage itself, and just when I get close enough,

does that, that is a defensive display.

It's incredible how adaptive these creatures are.

Not only able to change color,

but also able to change their shape

and skin texture completely.

Seeing these behaviors is very rare.

This is actually the first time I've ever witnessed it.

Now let's talk about danger.

All octopus are venomous, including this one.

And use their beaks to inject their prey

with a toxic saliva that paralyzes them

while they're consumed.

However, unlike their smaller cousin,

the blue-ring octopus,

this species does not have a lethal bite

when it comes to humans.

But besides their venomous ways and bizarre appearance,

these animals are indeed strange.

Having three hearts, 360 degree vision,

and possessing inexplicable intelligence,

has some scientists suggesting that these creatures

are indeed aliens from another world.

In fact, there are few fossil records to suggest otherwise.

But we'll save that debate for another video.

(dynamic music)

Okay, well our computers are telling us

it's time to return back to the surface.

But what an epic way to end our adventure.

If you thought the reef squid and the octopus

were bizarre just wait until you learn

the alien-like features of the snowflake eel.

Believe me, there are things about this animal

that will certainly shock you.

Click the next video to find out.

(animals calling)