If a predator is below the hatchetfish looking up, the predator will not be able to see anything at all, as the dim blue light blends right in with the rest of the water.

Each different species of hatchetfish displays different light patterns on their bellies.  

"Counterillumination" is the term for the way they use their camouflaging bioluminescence.  

The frilled shark has been around the block, as this species has existed for more than 80 million years.

Ludwig H.P. Döderlein, a German ichthyologist, discovered the frilled shark during the nineteenth century.

With a unique mouth shape and eerie appearance, many people refer to this shark as a "living fossil."

If the frilled shark wasn't scary enough, the goblin shark might give you nightmares.

This rare shark species is creepy and unusual, often described as "fossil-like."

You could easily pick it out of a police lineup thanks to its distinctive snout and pink-toned skin. It also has incredibly sharp teeth and a skinny, protruding jaw.

Zombie worms belong to the family of deep-sea siboglinid polychaetes. They are often referred to as "Osedax," which is Latin for "bone eaters." Zombie worms have the unique ability to burrow into a bone and eat it from the inside out.

You'll often see these worms feeding on the bones of whale carcasses that sink to the bottom of the sea.

There are special lipids inside bones that act as delicious meals for them. To bore into dense bones, they must use special root tissues.

The dumbo octopus is part of the umbrella octopus family.

If you're wondering, it gets its name from Dumbo the elephant, the friendly little character from Disney's 1941 animation, as it looks very similar.

Researchers first discovered the dumbo octopus in 1883, though the very first live dumbo octopus was not discovered until the 1990s when researchers got a deep-sea submersible down to the bottom of the ocean.

The barreleye fish might be one of the most unique Mariana Trench creatures in that its body looks like transparent plastic.

When looking at a barreleye fish, you can see all of the contents inside of its body.

It also has a transparent head that is filled with fluids, which makes it all the more alien-like.

With flat fins and a collapsible body, it is able to thrive more than 2,500 feet below the surface.

Another transparent bottom-dweller is the telescope octopus.

With eight tiny tentacles and a near-colorless body, this creature is a sight to behold.

The first person to ever observe this rare species was Dr. William Evans Hoyle in 1885.

To this day, we still don't know much more than Hoyle.

However, scientists believe that this octopus is a close glass octopus relative.

The sea cucumber makes up a good portion of life on the seafloor. What's incredibly unique about this creature is that it breathes through its anus.

This tiny sea creature has leather-like skin and a long body that can stretch and shape in unique ways. There are more than 1,700 sea cucumber species around the world, and while many live in the Mariana Trench, most of them live in the Asian Pacific Ocean. As you may have guessed, they get their name from their shape, which closely resembles that of a cucumber.

With luminous body structures and gelatin-like structures, comb jellies diffract light that hits them.

This creature gets its name from the comb-like plates found in its body that help it move throughout the ocean.

What's unique about this deep-sea predator is that it is one of the greediest creatures around, so much so that it'll often eat other comb jellies, even when other food is available.