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The Living Ocean

The oldest living thing on Earth might be a meadow of grass under the sea, and almost nobody has seen it. Most of the planet is water, most of that water is dark and cold, and here is some of what lives down there, in the highest resolution I could find.

A silvery school of fish hovering over a green seagrass meadow in clear blue water.
Neptune grass · Posidonia oceanica · one clone ~100,000 yrs oldThis whole meadow off Ibiza is one plant, a single clone roughly 100,000 years old. It was already ancient when humans painted the first cave walls.
A dense heap of purple and orange sea stars piled on intertidal rock.
Ochre sea stars · Pisaster ochraceusThis is the animal that gave science the term keystone species. Pull it off the rock and the whole community comes apart behind it.
A small oval chiton with psychedelic pink, blue and orange zigzag stripes across its eight plates.
Lined chiton · Tonicella lineataIt scrapes algae off rock with a tongue tipped in magnetite, which is iron ore. There is a magnet's worth of metal in its mouth.
A sunlit coral outcrop of staghorn, plate and boulder corals with small fish hovering above in blue water.
Great Barrier Reef · Flynn Reef, Australia · ~2,900 reefsThe only living structure you can see from space is not one reef. It is nearly 3,000, built grain by grain by trillions of coral polyps over 20,000 years.
A small fish patterned in a psychedelic maze of electric orange and cyan-blue.
Mandarinfish · Synchiropus splendidusAlmost every blue animal is faking it with light tricks. This is one of only two known to make the color with real blue pigment, and it skips scales entirely, wrapped instead in a foul toxic slime.
A cobalt-blue eel with flared yellow nostril flaps curling out of a reef.
Blue ribbon eel · Rhinomuraena quaesitaEvery electric-blue ribbon eel is male. Live long enough and it turns yellow and becomes female, switching sex and color at once.
A banded brown-and-white octopus with long arms fanned out over dark volcanic sand.
Mimic octopus · Thaumoctopus mimicus · copies 15+ animalsNo other animal is known to do this on purpose. It reshapes its body and arms to pass for a sea snake, a lionfish or a flatfish, picking the disguise to match the threat.
A small octopus with translucent veined webbing perched on a shell against dark sand.
Coconut octopus · Amphioctopus marginatusOne of the few invertebrates known to use tools. It collects coconut and clam shells, carries them along, and snaps them shut around itself as portable armor.
A small ochre octopus covered in glowing electric-blue rings on dark ground.
Blue-ringed octopus · Hapalochlaena sp. · venom for 26 adultsIt is smaller than a golf ball and carries enough toxin to kill 26 adults in minutes. There is no antivenom. The blue rings light up about a second before it bites.
A mantis shrimp airbrushed in every color at once, all reds, greens and blues, on the seabed.
Peacock mantis shrimp · Odontodactylus scyllarus · punch ~23 m/sIts club swings so fast the water itself boils for an instant, with a flash of light and heat. The blow lands at about 1,500 newtons, enough to crack aquarium glass.
A velvety black sea slug piped in neon green and orange.
Variable neon slug · Nembrotha kubaryanaIt eats sea squirts, keeps their toxins, and oozes them back out as a defensive slime. Those same chemicals are now being studied as anticancer drugs.
A small electric-blue sea slug with winged, finger-like appendages on pale sand.
Blue dragon · Glaucus atlanticusThis slug is the size of your thumbnail. It eats the Portuguese man o' war, saves the stinging cells, and packs them tight enough that its own sting beats the one it stole.
A small white crab covered in red polka dots sitting on a folded carpet anemone.
Porcelain crab in an anemone · Neopetrolisthes maculatusIt lives in the stinging anemone and fishes from it, fanning out feathery nets to strain plankton from the water. Grab it and it drops a leg and walks away.
The electric blue and magenta gas float of a Portuguese man o' war at the surface.
Portuguese man o' war · Physalia physalisThis looks like one animal. It is really a colony of tiny clones, none of which can survive on its own. Each is built for a single job: the purple gas float you can see, the long stinging tentacles, the feeding mouths, the breeding parts, all sailing the open ocean together as one body.
A glowing, perfectly symmetrical glass dumbbell-shaped radiolarian skeleton under the microscope.
Radiolarian · Stylosphaera coronata laevis · single cellEach radiolarian is one living cell. It pulls silica from seawater and spins itself this ornate skeleton, the same material as glass. When they die the tiny glass shells rain down and pack into deep-sea sediment hundreds of metres thick.
Star-shaped colonial diatoms radiating outward like a firework under the microscope.
Diatoms · light micrograph · ~20% of our oxygenRoughly one breath in five comes from diatoms, about a fifth of the oxygen you breathe, made by specks too small to see drifting in sunlit seawater.
A circular diatom shell forming a mandala of evenly spaced honeycomb pores.
Diatom shell · Stephanopyxis grunowiiThe pores sit on such an exact grid that engineers study diatoms as ready-made blueprints for photonic crystals and nanoscale filters.

where the sunlight gives out

Into the Dark

A deep-sea barreleye fish with two glowing green tubular eyes visible through its clear head.
Barreleye · Macropinna microstomaThose two glowing green orbs are its eyes, aimed straight up through a clear dome of a forehead. The dome is so delicate it falls apart the moment the fish is brought to the surface.
An orange-and-glass rocket-shaped siphonophore colony hanging in black water.
Siphonophore · Marrus orthocannaAgain this is a swimming colony, not one animal, a string of identical clones each doing one job. Some of its relatives grow longer than a blue whale.
A pale segmented worm crowned with scarlet gill filaments on a black background.
Pompeii worm · Alvinella pompejana · tail near 176 FMaybe the most heat-tolerant animal alive. It builds a papery tube on the wall of a deep-sea hydrothermal vent, the towering mineral chimney called a black smoker. Its tail sits near 176 F down in the chimney while its head leans out into 72 F water, a gap of about 100 F across one body.
A close portrait of a leopard seal's reptilian head and wide, smiling jaw at the surface.
Leopard seal · Hydrurga leptonyxIt is one of the only seals ever known to kill a person. A wild one once spent four days trying to feed a National Geographic photographer instead, bringing him live penguins, then dead ones, apparently deciding the clumsy human would starve on his own.
A pod of sperm whales hanging vertically in deep blue open water like floating monoliths.
Sperm whales · Physeter macrocephalus · largest brain on EarthThey sleep standing straight up in the water, in ten-minute naps, less than any other mammal. They also carry the largest brain of any animal that has ever lived.
A manta ray seen head-on with cephalic fins unfurled and mouth open into a dark oval, mid barrel-roll.
Giant manta ray · Mobula birostrisMantas have the largest brain-to-body ratio of any fish, and they pass the mirror test, recognizing themselves in a reflection. The only other animals that do are apes, dolphins and elephants.
A great white shark at the surface with its jaws agape, ragged teeth fully exposed.
Great white shark · Carcharodon carchariasA great white named Nicole, tagged off South Africa, swam the full width of the Indian Ocean to Australia, about 11,000 km in 99 days. Then she turned around and was home within nine months, the longest journey ever recorded for a shark.
A green sea turtle hanging in glassy blue water in a clean light gradient.
Green sea turtle · Chelonia mydasA green turtle feeding off Brazil will swim more than 2,000 km across the open Atlantic to Ascension Island, a speck of land a few miles wide. She nests on the same beach where she hatched decades earlier, often within a few kilometres of the exact spot.

the ocean is still mostly unmet

Discovered Just Now

A translucent, faintly glowing deep-sea slug with a billowing hood and a fringed tail in black water.
Described October 2024Mystery mollusc · Bathydevius caudactylusRobots filmed this glowing slug 157 times over 20 years before anyone could name it. Naming a new species means catching one to study its body and DNA, and this jelly-soft animal of the midnight zone was so hard to land intact that the proof took two decades. It turned out to be a slug that left the seafloor to swim, scooping up food in a billowing hood.
A pale gold wrasse with a bold inky spot near its tail.
Described 28 February 2024Tailspot wrasse · Halichoeres sancheziBoth fish here are the same species: (A) the red-headed adult male, and (B) a paler phase with the black blotch at the tail base, the 'tailspot' it is named for. It slipped past science until 2024 because it changes outfit as it grows, so the young, the females and the males look like three different fish.
An electric pink, magenta and orange wrasse against deep blue twilight-reef water.
Described 8 March 2022Rose-veiled fairy wrasse · Cirrhilabrus finifenmaaThis is a comparison plate, not a single fish. It sets the rose-veiled fairy wrasse next to the near-identical species it had been mistaken for, each shown alive in full colour (the vivid panels) and again after preservation (the pale blue-grey panels), once the colour has drained away. Its name, finifenmaa, means 'rose' in Dhivehi. It is the first new species ever formally named by a Maldivian scientist, in their own language.
A ghostly gem-like comb jelly with two long trailing tentacles, lit by an ROV in the dark.
Described 18 November 2020Duobrachium comb jelly · Duobrachium sparksaeIt is the first animal ever named as a new species purely from high-definition video, with no specimen caught at all. It drifts almost 4 km down like a balloon on a string.
A pale glass sponge on a thin stalk with a bulbous head and eye-like holes on bare deep seabed.
Described 9 July 2020E.T. sponge · Advhena magnificaIt looks like a jellyfish on a plant stem, and it is neither. It is a glass sponge, an animal whose whole body is the bulbous, eye-holed head, held up on a thin glassy stalk so it can sieve food from the passing current. Its name means magnificent alien. It looked so much like E.T. phoning home that scientists gave it a whole new genus, Advhena.
A neon pink-and-yellow striped fish in a dark crevice of a deep twilight reef.
Described 25 September 2018Aphrodite anthias · Tosanoides aphroditeHere the male glows in full neon (A) above a paler female (B). The fish so dazzled the divers who found it that they never noticed the sixgill shark circling above them. They named it for Aphrodite, the Greek goddess of beauty.

Sources

Every photograph here is public domain or Creative Commons, gathered from Wikimedia Commons, NOAA, MBARI, and other open archives. Each links to its source and license.