Happy World Oceans Day! We’re celebrating Earth’s oceans this whole week, with a series of videos about … the oceans. Turns out they’re full of some pretty weird things, and there’s a lot going on down there that we still don’t understand. And the deepest oceans are among the least understood habitats on Earth, because they’re hard for humans to explore. Never mind that it’s dark and scary down there, the pressure’s about a thousand times the pressure at sea level, which would compress the human body into a messy pulp.

But there is life down there, and plenty of it. We can study that life using either very long nets or remotely operated vehicles, known as ROVs. And each year, we’re discovering new, amazing species that are most at home in the ocean depths. These are 8 of the strangest deep sea creatures we’ve discovered, just since 2009.

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We’ll start off with the ninja lanternshark, which was brought up from deep waters off Central America. The species was officially described in 2015 by a research team led by marine biologist Victoria Vásquez . Four of her cousins, aged 8 to 14, helped coin the shark’s common name: ninja lanternshark. Which is actually really descriptive. Their skin contains bioluminescent organs called photophores, which give the shark an eerie green glow. These might help it do things like attract mates, communicate with other sharks, or lure prey.

But the ninja lanternshark is very different: it has fewer photophores and it has jet-black scales, which make it a great stealth hunter. It may not carry throwing stars or anything, but it does have some very sharp, asymmetric teeth, the top half are for grasping, and the bottom half are for cutting. Even if you encountered those teeth in their native habitat, though, you probably wouldn’t need to worry too much. Ninja lanternsharks are smaller than house cats and probably eat worms and small fish. But not all deep-sea creatures look quite as striking as the ninja lanternshark.

Sometimes, they just look like sad, washed-out old socks... Especially the sockworms, or Xenoturbella. They’re a group of five species, four of which were discovered in 2016 deep under the Gulf of California, using ROVs from the Monterey Bay Aquarium Research Institute. And if you’re thinking that their bodies look a little simple, you’re right. They’ve got a mouth, but no eyes, brain, or anus!

In fact, they’re so weird that scientists have struggled to fit them onto the evolutionary tree of life. Early DNA analysis suggested they could be some kind of strange mollusc that maybe lost some of its organs... but the researchers were misled by contamination from some clam eggs the sockworms had eaten. The evidence from the new species has helped researchers figure out what’s up with these sockworms, and these days, they’re thought to be some of the simplest animals with bilateral symmetry, a clear left and right side. As for those new species, the furrows in one of the new sock worms reminded researchers of a certain pastry, so they named this species Xenoturbella churro. I’m not sure I’d want one of these guys dipped in chocolate sauce, though!

Last year, the cold depths of the East Scotia Ridge near Antarctica revealed some of the habits of a species of crab with some very impressive body hair. First discovered in 2009, they’re unofficially called Hoff crabs after David Hasselhoff and his famous chest-rug, but those hairs aren’t for keeping the crab warm. Instead, they’re used to grow bacteria, which the crabs harvest using their comb-like mouthparts. Researchers from the UK took ROVs down to the polar depths, peering into the private lives of these crabs by examining how they were distributed across the ocean floor.

Their lives are mainly organized around volcanic vents, which warm the surrounding water. Males and females cluster together here, growing their bacteria, mating and presumably having a good time. The vents can support up to 4000 crabs per square meter. But there were also Hoff crabs living farther out from the vent, in the colder waters. These all turned out to be mothers, brooding baby crabs under their curled-up tails. The researchers think the vents could be spewing out chemicals that are toxic to the developing crabs. So the new mothers relinquish the safety and warmth of the group, but for the sake of the babies, it’s worth it.

The Hoff crabs were discovered in 2009, living in vents around 2.5 kilometers below the surface. Which is pretty far down. But just a year later, researchers from Southampton in the UK found some hot smokers twice that deep. At five kilometers down, these are the deepest known volcanic vents in the world.

And they’re full of life, specifically, a new species of eyeless shrimp. They’re found in the Mid-Cayman Rise, a huge seafloor gash caused by two tectonic plates ripping apart. Like the Hoff crabs, these shrimp take advantage of the warmth provided by these volcanic vents, and there are huge swarms of them down there. The vents heat water to around 400 degrees Celsius, the only reason it doesn’t boil is because of all the pressure.

And just like we humans might enjoy the heat of a bonfire, but only from a safe distance, the shrimps also want to avoid the scalding danger zone. But they need help to avoid bumbling straight into it. Eyes as we know them aren’t going to be much help, since it’s pitch black down there and the vents don’t emit any visible light! The baby shrimp are born with eyes that can sense visible light, since they live a little closer to the surface. But as they mature, they do away with eyes completely, and develop an infrared, heat-sensing organ on their backs to avoid becoming another shrimp on the Barbie.

Any list of deep sea creatures wouldn’t be complete without an appearance from our favorite underwater horror, the anglerfish! There are more than 200 known species of anglerfish, and this new one, well... it’s not pretty. The story of this snaggletoothed brute’s discovery doesn’t start happily. In 2010, offshore oil rig Deepwater Horizon exploded and sank, spilling 5 million barrels-worth of oil into the Gulf of Mexico, an ecological disaster. Very little was known about what species lived in the area, especially deep underwater, and this made clean-up and conservation efforts a lot harder. Extensive surveys of life in the Gulf discovered fifty new species, including this ugly beast. Those forehead spikes are actually teeth! Its upper jaw is highly mobile, so it can reach all the way up there and grab anything that swims too close to its glowing lure.

Female anglerfish also use their lures to attract males, but they only want males from their own species. So each anglerfish species has its own signature lure structure, which affects the fish’s appearance in the dark ocean depths. This makes lures great clues to help researchers figure out if they’ve got a new anglerfish on their hands. This new anglerfish’s lures each have a finger-like extension that guides light like a fiber-optic cable. They also have two filaments near the tip, which might mimic wiggling prey. Sometimes you just need to get up-close-and-personal with even the most hideous of species, if you want them to reveal their secrets.

In 2012, MBARI’s ROVs discovered the Gulf of California’s depths are home to the rather graceful-looking harp sponge. Its root-like attachments may look plant-like, but sponges are actually animals, though fairly simple ones. Despite its name, the harp sponge won’t be playing you any elegant tunes, it’s up to something much more sinister! It spreads out in a fan-shape, with up to six vanes extending from the rooted center to maximize the chances of making a catch.

Each so-called “string” is coated in barbed hooks, which snare creatures that happen to pass by and decide the gently waving branches would be a nice place to hang out. The sponge then coats its seafood entrée in a thin membrane and digests it whole. Most shallow water sponges are filter-feeders that capture bacteria or debris and extract the nutrients, but the sparse ocean depths require different tactics. So until around 20 years ago, we didn’t know that some sponges eat meat at all. Now that marine biologists have a better idea of what to expect, they’ve discovered dozens of new carnivorous sponges. And those nodules at the top? They’re full of sperm! The bulbs distribute sperm into deep-sea currents, hoping to find the eggs on the strings of other harp sponges.

The species we’ve talked about so far are just some of the new creatures scientists have discovered since 2009. But there are some new creatures that we’ve seen for the first time in just the last few months! So researchers haven’t had time to go through the rigorous process of officially describing them yet. This one is a type of octopus that was found four thousand meters down, near Hawaii, by NOAA’s Deep Discoverer ROV.

It’s so new to science, it might even be a whole new genus. It doesn’t have an official name yet. But people have taken to calling it “Casper”, after the friendly ghost, and it’s not hard to see why. The striking lack of color is pretty strange among cephalopods. Many have astounding colour palettes, thanks to specialized pigment cells called chromatophores. Cephalopods can adjust the behavior of these cells to create impressive displays or melt into the background. But Casper doesn’t seem to have any chromatophores, leaving it with a ghoulish white hue.

Another surprise was that it’s only got one row of suckers running along its tentacles compared to the usual two rows found in most kinds of octopus. How these features might help Casper survive is still a mystery, and it’ll probably probably stay that way until we can find more Caspers to study.

An even more recent finding, from April 2016, was this stunning jellyfish, captured on film by NOAA’s Okeanos Explorer team. The team was on a mission to explore the region surrounding the Marianas Trench, which contains the deepest waters on Earth. This mission has a bunch of objectives, like revealing the trench’s geologic history in more detail. But it’s also looking for life. Just in the first few days of the mission, which runs through July 10th, the team spotted some deep-sea gems, including this jellyfish, which seems to be completely new to science.

It doesn’t have a specific name yet, but the researchers’ best guess is that it’s a form of hydromedusa, and part of the Crossota genus. The red lines are called radial canals, they help link body parts together, including those yellow orbs, which are probably reproductive organs. We don’t know how this jellyfish lives, but other Crossota species are ambush predators, so this one might be, too. This could explain how it’s behaving here: floating with sprawling tentacles, waiting for something to stumble by into a world of sting.

With so much of the ocean still to explore, and new deep-sea research missions happening across the world, this is an exciting time to be interested in life beneath the waves.

Thanks to Victoria Vásquez, Kim Fulton-Bennett, Jonathan Copley, and Theodore Pietsch for their help with this episode, and thanks to all of our patrons on Patreon who make this show possible. If you want to help us make videos like this, just go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!