You know how there's about 95% of the ocean that still categorized as "unexplored?" It's a pretty terrifying thought, really, when you pause to remember just how much of the Earth's surface is covered in water and what might be lurking down there. But if you're a citizen of Atlantis, the unknown parts of the ocean may actually be considerably less horrifying than the parts that have come to light.

Meet the Trench. They're here and they're hungry.

They also make a pretty breathtaking—and terrifying—appearance in James Wan’s Aquaman, figuring heavily in a pivotal sequence that draws generously from Wan’s horror movie roots. So, to make sure you’re not caught completely off-guard by it, we thought we’d take a look at these monstrous undersea villains and dive into their comic book past. But before we go any further, we just want to ask...

You’re not planning on taking any cruises or sailboat excursions over the holidays, are you?

If you are, you may want to stop reading right about here. At least if you don’t want to spend your time at sea looking around in abject terror. But for the rest of you, let’s talk Trench!

Introduced in Geoff Johns and Ivan Reis’s AQUAMAN #1 back in 2011, the Trench are a race of monstrous sea creatures who came from—you guessed it—a trench in the bottom of the sea. Actually, not just any trench, the Marianas Trench, one of the deepest and most mysterious canyons in the ocean floor.

The Trench aren't exactly autonomous entities. They exist as a sort of ravenous collective with every member of the species looking and acting nearly identical to the next. The sole exceptions are their king and queen, who are able to force the rest of the horde in line, at least when it comes to claiming whatever food might be in their path. But this wasn't always the case. The real story of the Trench begins a long, long time ago back at the dawn of Atlantean civilization.

It turns out the Trench used to be normal, human-looking Atlantean citizens, back before the city sank beneath the sea. When King Atlan drowned the city, the surviving Atlanteans were split off into not two, but three independent groups: the Atlanteans we know today, the Xebelians who existed in the Bermuda Triangle, and the Trench who fell into the deepest parts of the sea. (This is slightly different from the movie, in which there were seven groups that split off.) Thanks to their isolation and extreme conditions, the Trench evolved, or perhaps devolved into a monstrous, mindless swarm set on consuming anything in their path.

But one thing you might want to understand about the Trench is that they have a good reason for this. The reality of their existence is pretty dire. The unforgiving and harsh ecosystem they live in means that they're running out of food to support the continuation of their species. Their ravenous, brutal appetites aren't always the product of a wanton need to destroy—they're also looking for a way to ensure that their race doesn't simply die out.

So, as you might imagine, things are a little complicated for Arthur and Atlantis in terms of what the best course of action for their people may be.

But wait, there's one more detail about the Trench that’s worth pointing out. They can also be controlled. The Trench will listen to the orders of whoever holds the scepter of Atlan. You can see this in action if you take a look back at JUSTICE LEAGUE: THE THRONE OF ATLANTIS, where the Trench is weaponized to force Atlantis and Aquaman into a corner.

As you might be able to guess, things tend to get a little bit messy when the Trench get involved, no matter what brings them to the light of day. That’s very much true in Aquaman’s big screen adventure, so keep an eye out when you hit the theaters this weekend, and keep your arms and legs in. People who go seeking the Trench don’t tend to return…

Aquaman, directed by James Wan and starring Jason Momoa and Yahya Abdul-Mateen II as Black Manta, splashes into theaters tomorrow.

Meg Downey covers movies, TV and comics for, and writes about Batman each month in her column, "Gotham Gazette." She's also a regular contributor to the Couch Club, our weekly television column. Follow her on Twitter at @rustypolished.