Mariana Trench animals occupy one of the deepest and darkest pits of the oceans (though it's not the world's deepest continental trench). It’s a location so hard to get to that there have been more humans in space than at the bottom of the Mariana Trench, and while we’ve identified a few species that pass through here it’s likely that there are many more we’ve yet to find.
Right now, you’re experiencing an atmospheric pressure of around 7 kilograms (14.7 pounds) per square inch (PSI) – but were you to teleport to the bottom of the Mariana Trench, you’d experience pressures of more than 16,000 PSI. This dramatic difference has shaped Mariana Trench animals, and coupled with the extreme darkness, it’s made for some truly wacky deep-sea species.
Mariana Trench animals like the pressure
To have an idea of what that does to an animal, you need only look to the blobfish. It’s become famous as arguably the ugliest fish in the ocean, but the accolade is perhaps a little unfair considering it’s based on how this fish appears at surface level.
Down in its natural habitat around 610 - 1220 meters (2,000 – 4,000 feet) below the surface, it looks quite normal – but when you drag it up to a lower atmospheric pressure it basically, very passively, explodes. This demonstrates the extremes that Mariana Trench animals have evolved to thrive in, which is why it’s home to some of the weirdest species on the planet.
Mariana Trench animals: Goblin shark (Mitsukurina owstoni)
Goblin sharks were first described over one hundred years ago, but still don’t know a huge amount about them because they live so deep that very few specimens have been found for research. Specimens that have been obtained tend to come about as accidental bycatch, but this is rare because they don’t typically live at depths within fishers’ reach.
These bizarre creatures of the deep are the only surviving representative of the Mitsukurinidae family, which dates back some 125 million years.
They have a sensory system known as ampullae of Lorenzini along their snouts that can detect weak electrical impulses in the water, like the passing pulses of potential prey. If they pass within reach of a victim, their jaws explosively catapult forward, piercing it with needle-like teeth that have evolved for spearing rather than cutting.
Mariana Trench animals: Black seadevil (Melanocetus)
Finding Nemo fans might recognize the terrifying black seadevil, an alien-like anglerfish with a bioluminescent lure it uses to attract prey in the blackness of the deep sea. In 2014, the Monterey Bay Aquarium Research Institute (MBARI) captured footage of a living black seadevil for the first time. While it might look frightening, with barbed teeth lining its gaping mouth, black seadevils typically measure around 20 centimeters (8 inches).
Mariana Trench animals: deepsea dragonfish (Stomidae)
Measuring just 15 centimeters (6 inches) in length, the dragonfish (Aristostomias scintillans) has an “enormous” jaw relative to their size, capable of extending and opening beyond the abilities of a conventional jaw. It’s also lined with dozens of fang-like teeth sharper than those found in a piranha. To keep their prey in the dark, the teeth of dragonfish have evolved a transparent structure that essentially makes their fearsome mouth invisible.
Dragonfish have small photophores that generate light for attracting prey, but with such big teeth, they’d risk giving the game away if their spiky gnashers reflected that light. Research has shown that they’ve evolved transparent teeth to overcome this, meaning they’re both excellent predators and master hiders.
Mariana Trench animals: dumbo octopus (Grimpoteuthis)
The deepest living of all octopuses, the dumbo moves about the deep ocean by flapping ear-like fins as they use their arms to steer. They’ve adapted to the poor dating scene of deep-sea life by becoming the ultimate opportunists, as females will carry eggs in different stages of development. This means should they cross a male, they’re good to go and can hold onto sperm until the environmental conditions are most favorable for producing offspring.
Mariana Trench animals: Barreleye (Macropinna)
Found at depths most light can't reach, these truly bizarre animals are equipped with a see-through head, allowing their eyes to effectively look out of the sunroof as they navigate the pitch-black waters. The barreleye’s eyes aren’t those two indentations you see in the conventional eye position, but are actually the glowy green balls sitting slightly further back. The circles at the front are olfactory organs that can “smell” chemical cues in the water. You can see a living barreleye swimming here.
The function of the eyes’ strange positioning, MBARI says, is to spy prey above them, which they’ll sometimes steal from the dangling tentacles of siphonophores. As ultra-sensitive tubular eyes, they are incredibly well adapted for spotting the silhouettes of edible animals against the minuscule amount of light that travels to such depths. At one point, it was thought the barreleye’s eyes were constantly to the sky, but it’s since been established that they can roll to face forwards when eating.
Mariana Trench animals: frilled shark (Chlamydoselachus anguineus)
This primitive shark gets its name from the six frilly gills that sit along its snake-like body, which is the inspiration for its Latin name Anguineus. They’re thought to have remained unchanged for millions of years, having evolved the perfect morphology for deep-sea living.
Frilled sharks’ large mouths are lined with multiple rows of three-pronged teeth that are hooked to better hold onto prey. With around 300 teeth in total, captured animals are unlikely to escape the frilled shark’s grip.
Mariana Trench animals: half-naked hatchetfish (Argyropelecus hemigymnus)
Cover your eyes, children, the half-naked hatchetfish forgot its pants. These peculiar mini fish are perpetual optimists with eyes pointed upwards that have large pupils capable of picking out even camouflaged animals drifting through the water column.
It’s also a master camouflage itself, with pale blue lights on its belly that help it to diffuse its silhouette by mirroring the light above. This is a common adaptation among twilight zone animals who exist caught between the blackness of the seabed and the faint light from the water’s surface.
Mariana Trench animals: snailfish (Pseudoliparis swirei)
Meet the world’s deepest fish. The gelatinous snailfish has been found at depths surpassing 8,000 meters (26,200 feet), making it the deepest living fish known to science. Called the Mariana snailfish, it's been spied with the aid of remotely operated vehicles (ROVs) multiple times in the Mariana Trench.
Surface specimens look a bit like a chicken breast morphed into a tadpole, but like the blobfish, this is because the animal deforms with the dramatic shift in atmospheric pressure. When swimming at its preferred watery depths, it is a shimmering pearlescent creature with translucent skin and no scales.
Mariana Trench animals: vampire squid (Vampyroteuthis infernalis)
The sanguine coloration of vampire squid earned them a nickname inspired by the undead bloodsuckers of lore, with a cape-like webbing of skin between their arms to boot. They aren’t immortal, but their lifespan is longer than most cephalopods because they live at a slower pace, inhabiting the open ocean at depths of 500 to 3,000 meters (1,600 to 9,800 feet).
At this depth, life is less about swimming and more about floating, which means only needing a little oxygen and getting by on a low-calorie diet of zooplankton and miscellaneous detritus. Vampire squid also have a more active sex life compared to most cephalopods, having multiple reproductive cycles while other species have just one.
Mariana Trench animals: zombie worms (Osedax)
Zombie worms are big fans of dead bodies – those of whales, specifically. Osedax means “bone eater” and it refers to the way these worms will bore into carcasses and reach the fatty lipids locked inside their skeletons. A thirst for whale sinks and other dead animals means evolving to occupy life on the seafloor, and zombie worms were first identified at an incredible depth of 3,000 meters (10,000 feet).
A successful zombie worm is all about teamwork, with the females doing most of the work. They drill into bone using acids that free up the lipids, which are then processed with the help of symbiotic bacteria. It could be argued that the male isn’t exactly pulling its weight, but considering he’s a microscopic organism stuck inside the female's body – and probably just one of hundreds – it’s perhaps not reasonable to expect much from them other than sperm.
So as you’ve probably surmised, it’s pretty hard to pigeonhole Mariana Trench animals. From terrifying teeth to adorable flapping “ears” and a love story between one big worm and her 100 microscopic mates, these species demonstrate how evolution can give rise to animals capable of living in the extremes of environmental conditions.