Scientists used to believe that few species could survive in the pitch-dark, freezing-cold depths of the ocean, where the weight of the water creates immense pressure. But we know now that even the deepest ocean floors teem with life. Many of the creatures in the deep have evolved fascinating adaptations to deal with their challenging environment, such as translucent skin that blends into the dark water, huge jaws for grasping the scarce prey, long legs to navigate the rocky seafloor, and organs that glow in the dark. And while we sometimes don’t know much about these species given their hard-to-reach habitat, marine scientists are learning more all the time.
Bloodybelly Comb Jelly
Despite the “jelly” in their name, comb jellies are not actually jellyfish — they're a different type of creature altogether. They have eight rows of combs, or cilia — little translucent hairs that beat to propel them through the water. These stunning sea creatures are known for the disco-worthy show they produce when hit with a beam of light from an underwater vessel; the light scatters along the cilia to produce a rainbow effect. The light looks especially gorgeous on the deep-red bloodybelly comb jelly (Lampocteis cruentiventer), which lives between about 1,200 and 3,200 feet down in the northeast Pacific. Although the bloodybelly comes in different shades of scarlet, its stomach is always blood-red, which scientists think may help disguise the bioluminescent prey it eats so that the bloodybelly itself doesn’t become a snack. And while the crimson hue looks startling to us, in the lightless deep ocean it fades to black, allowing the bloodybelly to stay well-hidden.
Warty Seadevil
Warty seadevils are the largest of the anglerfish, a group named for their dorsal spines, which dangle a fleshy and often bioluminescent “bait” to attract prey. (As The New York Times put it, they are “fish that fish.”) Only the females have this lure, however, and the much-smaller males have evolved a strange trick to keep from swimming the depths forever in search of a mate. Once they reach adulthood, a male seadevil will bite a female and then fuse with her circulatory system, drawing nourishment from her blood while releasing sperm as necessary. He stays in this parasitic embrace for the rest of his life, while his eyes and fins atrophy. More formally known as the Ceratiidae family, these bizarre creatures live in the Atlantic, Pacific, and Indian Oceans.
Dumbo Octopus
Unlike the blobfish, the dumbo octopus is downright adorable. The name refers to a whole genus of deep-sea octopuses named for the Disney protagonist, due to their fins that resemble elephant ears. They’re part of a group called umbrella octopuses, because they have webs of skin that look like umbrellas when their tentacles spread apart. These cute critters, which come in a range of colors, live deep in the open ocean worldwide, at depths of at least 13,000 feet. They’re naturally rare, so they’ve evolved some mating strategies to allow them to reproduce whenever they find a mate, one of which includes the females constantly carrying eggs in all stages of development.
Vampire Squid
Despite its fearsome-looking tentacles and startling name, this creature is not terribly threatening — it’s only about as big as a football. (The first scientist to describe it, Carl Chun, gave the species the Latin name Vampyroteuthis infernalis — "vampire squid from hell” — because its dark coloring, glowing red eyes, and cloak-like webbing apparently suggested a vampire.) Vampire squids are also the only known cephalopod that don’t catch live prey for food, and instead feed on “marine snow,” a charming name for an un-charming substance mix of dead animals, mucus, and feces. The animals themselves can be pale to deep red or black, and live between about 2,000 and 10,000 feet down across the world’s tropical and temperate oceans. Technically, they’re not squids, or octopuses, but have characteristics of both and belong to their own order, Vampyromorphida.
Japanese Spider Crab
The Japanese spider crab (Macrocheira kaempferi) can grow 13 feet from end to end, making it the largest of the spider crabs and possibly the largest known arthropod. Its unusually long legs help it stroll around the sloping sea floor. These spider crabs live in deep waters of the Pacific near Japan (up to about 2,000 feet down), although they move to shallower areas during spawning season.
Barreleye
The barreleye fish (Macropinna microstoma) has one of nature’s most unusual heads: It’s completely transparent and filled with fluid. For decades, marine biologists thought its large, bright-green eyes were only able to stare straight ahead, but recent studies by the Monterey Bay Aquarium Research Institute have shown that the eyes can rotate upward to look through the transparent head for food, or point forward when the fish is feeding. The eyes are also extremely sensitive, which helps barreleyes search for faint outlines of prey in the dark waters of the North Pacific.
Sloane’s Viperfish
The slender, iridescent Sloane’s viperfish (also called Sloane’s fangfish), or Chauliodus sloani, is one of nine species of viperfish that live deep in the world’s tropical and temperate oceans. The first part of its name comes from the British naturalist and collector Sir Hans Sloane, while the second part comes from the long fangs that stick up from both its upper and lower jaws, which help it grasp wriggling prey. These fish live deep down, between 3,200 and 6,500 feet, although they rise to shallower locations during the night.
Blob Sculpin
Yes, this blobfish (Psychrolutes phrictus) is pretty ugly by human standards — a related species was even named the world’s ugliest animal. This particular blobfish, part of the Psychrolutidae (“Fatheads”) family, lives between 1,600 and 9,000 feet down in the North Pacific. Like many other deep-sea creatures, they have a minimal skeleton and little muscle, an adaptation that helps them survive the immense pressure. They don’t look so bad in the deep sea, but bringing them up to the surface turns them into distasteful-looking piles of jelly.