Vertebrate and cephalopod camera eyes evolved independently, but their retinas are wired differently. In vertebrates, nerve fibers lie in front of the photoreceptors and the optic nerve creates a blind spot. In octopuses, the photoreceptors face incoming light and the nerve fibers exit behind them, so there is no comparable blind spot.
In 2021 researchers confirmed that the kitefin shark, a deep-sea species reaching about 5 ft 11 in (1.8 m), produces its own blue-green light — making it the largest known luminous vertebrate on Earth. Its glowing belly likely erases its silhouette against the faint light above, a cloaking trick called counterillumination.
Nurse sharks generate suction among the strongest measured in any fish, inhaling prey from crevices with a sound like a slurp — one possible origin of their name. They can pump water over their gills while lying still, so they spend daylight dozing in piles on the seafloor.
In Hawaiian tradition, certain sharks were ʻaumākua — ancestral guardian spirits of specific families — fed, respected and never hunted by those they protected. The man-eater of one culture's nightmares was another culture's grandmother.
Most octopus species live for roughly a year or less. The giant Pacific octopus is unusually long-lived at about three to five years, while the deep-sea Graneledone boreopacifica has been recorded brooding its eggs for 53 months.
Named for its schedule, the night shark spends days hundreds of meters down and rises toward the surface after dark, guided by oversized eyes with a vivid green shine. Fishermen named it before scientists explained it. Its workday begins when the ocean's lights go out.
Sharks were long assumed to follow the stronger scent, but a 2010 experiment on smooth dogfish — fitted with headgear that piped squid odor to each nostril separately — showed they turn toward whichever nostril catches the smell first, even when the other nostril gets the stronger dose, on time gaps as short as a tenth of a second. Odor in the sea arrives in ragged patches, so timing beats concentration for tracking a plume back to its source. The researchers suspect the hammerhead's wide-set nostrils sharpen this stereo sense further. The famous nose is less a detector than a compass.
The siphon is a muscular funnel that forcefully expels water from the body. An octopus uses it for jet propulsion, to eject ink, and to aim water beneath the arm web strongly enough to throw silt, shells and other debris.
Female sharks of several species can store viable sperm in specialized glands for months to years after mating — one brownbanded bamboo shark produced a pup after 45 months of isolation, a record documented in 2015. Shark family planning operates on geological patience.
The octopus genome contains 168 protocadherin genes, which help regulate how neurons develop and connect. That is about ten times the number found in other invertebrates and more than twice the number in mammals. Large protocadherin families had previously been considered mainly a vertebrate feature.
Before petroleum, oil rendered from shark livers lit lamps, tanned leather and greased machinery; entire fisheries — from Achill Island's basking sharks to the World War II hunt for vitamin A-rich soupfin sharks — rose and crashed on shark oil. Sharks powered human nights before electricity did.
Global assessments led by IUCN specialists conclude that roughly one in three species of sharks, rays and chimaeras is threatened with extinction, chiefly from overfishing. The animals that outlasted five mass extinctions are struggling with a sixth made of nets and hooks.
Because cartilage rarely fossilizes, the shark fossil record is overwhelmingly teeth — shed continuously for 400 million years — plus occasional vertebrae and rare body impressions. Some fossil beds hold thousands of teeth per square meter. Sharks wrote their autobiography almost entirely in bite.
The dwarf lanternshark of the deep Caribbean matures at around 6 to 8 inches (15–20 cm) — smaller than many goldfish — and carries light-producing organs along its belly. The ocean's most feared family includes a member you could hide in a coat pocket.
Radiocarbon from Cold War bomb tests, lodged in the growth bands of two dead whale sharks' vertebrae, proved in 2020 that each band marks one year — and put one shark, a 10 m (33 ft) female stranded in Pakistan, at 50 years old, the oldest ever verified. Earlier modelling built on those yearly bands suggests the largest may live a century. The biggest fish in the sea is also one of its slow-burning elders.
Behind its small gripping front teeth, the Port Jackson shark carries broad, flattened molars — crushing plates that pulverize sea urchins, snails and crabs. Its scientific name, Heterodontus, means "different teeth." It is a shark that grinds its dinner like a mill.
The underside of a hammerhead's wide head is studded with electroreceptors, and the shark swings it across the seafloor to scan for the faint fields of stingrays buried in sand — the width of the hammer widens the search area with every pass, an advantage Kajiura and Holland measured in 2002. Great hammerheads then use the hammer itself to pin a ray to the bottom while they bite. The strange head is both the search coil and the weapon.
Scientists fitted tiger sharks in the Bahamas with cameras and trackers, and the sharks' commutes across their feeding grounds helped confirm the largest known seagrass ecosystem on Earth — at least 66,000 km² (25,000 sq mi) and up to 92,000 km² (35,000 sq mi) across the Bahama Banks, enough to raise the world's known seagrass cover by more than 40% in a 2022 study. The apex predator moonlighted as a survey vessel.
Octopuses are carnivores, and for nearly every species studied the staple is crustaceans: crabs above all, with shrimp and lobsters behind them. Mollusks come second — clams, snails and scallops, pulled apart, drilled through or relaxed with paralyzing saliva. Larger species take fish as well. And the giant Pacific octopus is recorded eating smaller octopuses, its own species included.
Two close cousins carry opposite toolkits: the great white's broad triangular teeth are serrated like steak knives for shearing blubber, while the shortfin mako's are smooth, narrow spikes for pinning slippery fish. Read the tooth and you read the menu. In sharks, cutlery is destiny.
Sharks produce unusually small, rugged antibody fragments called VNARs — roughly a tenth the size of human antibodies — able to reach folds on viral proteins that larger molecules cannot. Lab studies have shown shark VNARs neutralizing SARS-CoV-2 and related coronaviruses, and researchers are developing them against cancers and other targets. The ocean's oldest immune system is auditioning for ours.
A shark's entire skeleton is cartilage — the same flexible tissue as a human ear — reinforced with mineralized plates where stress is highest. Cartilage is lighter and bends without breaking, part of why sharks are such economical swimmers. It is also why complete shark fossils are so rare while their teeth litter the world.
In History of Animals, Aristotle called the octopus a stupid creature because it would approach a person's lowered hand. Yet he also accurately described its specialized mating arm, a feature European naturalists later had to rediscover.
Small deep-sea lantern sharks grow light-producing organs called photophores along their undersides, matching the dim glow filtering from above so predators looking up see nothing. Some also flash light along spines and fins. In the deep, the best hiding place is brightness.
An octopus can rebuild a lost arm, including its muscles, suckers and nerve cord. The wound is first covered by a layer of epithelium, then new tissue is organized into the structures of a functional replacement arm rather than a simple scar.
In cephalopod anatomy, arms carry suckers along their whole length while tentacles are longer, retractable and suckered mainly at the tip. Squid and cuttlefish have both — eight arms plus two tentacles. Octopuses have eight arms and nothing else. The word "tentacle" is almost universally applied to them and is almost universally wrong.
A female giant Pacific octopus hangs her eggs from the roof of her den in hundreds of strands of roughly 250 eggs each, commonly totaling 18,000 to 74,000 and occasionally reaching 100,000. For six or seven months she fans them, cleans them and blows water over them, and does not eat. As the eggs hatch, she blows the young free of the den with her last strength, then dies. Each hatchling emerges the size of a rice grain, weighing about 22 milligrams, and of the tens of thousands, a handful will reach adulthood.
The mimic octopus, first seen off Sulawesi in 1998 and named Thaumoctopus mimicus, flattens, contorts and recolors itself into imitations of flatfish, lionfish and banded sea snakes. Reports credit it with impersonating a dozen or more marine animals, nearly all of them venomous or unpalatable.
The male seven-arm octopus (Haliphron atlanticus) hides its eighth arm, a specialized mating arm, in a pouch beneath the right eye, so only seven are visible. This deep-sea species feeds on jellyfish, eating the bell and sometimes carrying the trailing tentacles.
The pigeye shark — a stocky, snub-snouted, small-eyed cousin of the bull shark — patrols murky Indo-Pacific shallows and is so often mistaken for the bull that scientists struggle to count it. Its name is not a nickname; it is the official common name. Somewhere a shark answers, formally, to "pigeye."
With pectoral fins shaped like wings and a tail delivering forward thrust, many sharks fly through water more than they float in it — negatively buoyant bodies held aloft by hydrodynamics, sinking whenever they glide too slowly. A great white shark is, structurally, a heavier-than-water aircraft.
Across 500-plus species, sharks cover nearly every reproductive playbook: some lay armored egg cases, some nourish live young with placentas rivaling mammals', and some hatch eggs internally before live birth. No other vertebrate group mixes its maternity wards so freely.
Tiger sharks are the ocean's least fussy eaters: documented stomach contents include sea turtles, seabirds, other sharks — and human garbage from license plates to tires, which earned them the nickname "wastebaskets of the sea." Their serrated, can-opener teeth shear through turtle shell. Curiosity, in a tiger shark, is a digestive strategy.
The shortfin mako is the fastest shark in the world — a torpedo-shaped, crescent-tailed hunter that runs down tuna and swordfish in the open ocean.
Jacques Cousteau called the oceanic whitetip "the most dangerous of all sharks" — not for beaches, but for the open sea, where it reaches shipwrecks and air crashes first. It is widely implicated in deaths among the roughly 900 sailors set adrift by the USS Indianapolis sinking in 1945, though exposure and thirst killed many. The shark you have never heard of owns the ocean's worst disasters.
Feeding trials published in 2018 showed bonnethead sharks digesting and absorbing nutrients from seagrass, not merely swallowing it while hunting crabs — the first shark shown to be a true omnivore. More than half its diet can be plants. Somewhere in the hammerhead family, a shark went partly vegetarian.
In the late 1950s, Eugenie Clark trained lemon sharks at Florida's Cape Haze laboratory to push a target that rang a bell for food, then to pick the correct target over a wrong one — and after a 10-week winter layoff, the sharks took the task straight back up. In 2018, Port Jackson sharks in a Macquarie University lab learned to swim to a feeding station whenever a jazz track played, though asked to tell jazz from classical, they struggled. The reputation for mindless instinct does not survive contact with a curious shark.
Detached arms continue responding to stimuli and activating their suckers long after they lose contact with the brain — in laboratory observations, for more than an hour. In one experiment an octopus handled its own amputated arm freely but held it only at the skinless cut end and would not eat it. The self-recognition signal apparently survives the separation.
Helicoprion, a 270-million-year-old shark relative, grew a spiral whorl of teeth like a circular saw blade set in its lower jaw — a structure so bizarre that scientists argued for a century about where on the body it belonged until CT scans settled it in 2013. Evolution once shipped a power tool with fins.
Male argonauts detach a specialized mating arm inside the female, where it can continue moving on its own. In 1829, Georges Cuvier mistook these arms for parasitic worms and named them Hectocotylus octopodis. The term hectocotylus is still used for a cephalopod's specialized mating arm.
The first dinosaurs appeared roughly 230–240 million years ago; the shark lineage was already more than 200 million years old by then and had come through three mass extinctions — the end-Ordovician, the Late Devonian and the end-Permian, the worst of them all. When Tyrannosaurus finally showed up, sharks were the ocean's grizzled veterans. Dinosaurs came and went; the sharks stayed.
One of the world's most heavily fished sharks is also among its longest-lived: Pacific spiny dogfish are estimated to live 80 years or more, maturing only after decades. The 3-foot (0.9 m) shark defends that long life with two mildly venomous dorsal spines. Longevity in the sea does not require size.
Megalodon — Otodus megalodon, an extinct shark that hunted the world's oceans from about 20 million to 3.6 million years ago and is known mainly from its serrated teeth, some the size of a human hand — was far larger than any shark alive. A 2025 study by 28 specialists, comparing fossil vertebrae from Belgium and Denmark with the proportions of 165 living and extinct sharks, put its maximum length at up to 24.3 m (80 ft) and its weight near 94 metric tons.
Around Greenland, the sharks' eyes are frequently parasitized by Ommatokoita elongata, a pale copepod about 3 cm (1.2 in) long that anchors itself to the cornea — for decades, reason enough to assume the hosts were all but blind. A 2026 study of Greenland shark eyes found a pristine, purely rod-based retina tuned to deep-water blue, with no sign of degeneration even in a specimen more than 130 years old, and a cornea that still passes most light despite the parasite. Video shows the sharks turning their eyes toward light. The longest-lived vertebrate is not blind; it just lives where there is little to see.
The common octopus runs on roughly 500 million neurons, by far the largest nervous system of any invertebrate — a honeybee has about a million. Two-thirds of them sit in the arms rather than the central brain, each arm carrying a nerve cord that handles touch, taste and movement locally. The brain sets the mission; the arms work out the details.
Hunting seals at Seal Island, South Africa, great whites rocket upward from deep water and launch fully clear of the surface, striking from below at speeds researchers estimate near 40 km/h (25 mph) at breach. A two-ton fish becomes briefly airborne. The ambush comes from the third dimension.
Australia's wobbegong sharks are flattened ambush hunters fringed with weed-like skin flaps, camouflaged so well against reef floors that their name is thought to come from an Aboriginal word associated with shaggy beards. Prey swims to them. The rug moves last.
Two branchial hearts drive blood through the gills; a third systemic heart sends it out to the arms, organs and brain. When the animal jets, pressure inside the mantle stops blood returning, and the systemic heart — with nothing to pump — stops until the jetting ends. Fast swimming therefore starves an octopus of oxygen at the exact moment it needs it most. This makes sustained jetting physiologically costly compared with crawling.
In 2001 a hammerhead pup appeared in a Nebraska zoo tank holding only females, and DNA testing later proved the first confirmed virgin birth in sharks — parthenogenesis, reproduction with no father at all. Zebra sharks and other species have since repeated the trick in captivity. Some sharks simply do not wait for a mate.
Common octopuses can lay about 100,000 to 500,000 small eggs that hatch into planktonic paralarvae, while giant Pacific octopuses lay tens of thousands. Some deep-sea octopods produce only about 30 large, yolk-rich eggs whose young hatch as miniature bottom-dwelling octopuses.
Many sharks enter tonic immobility — a limp, trance-like state — when rolled onto their backs, a reflex researchers use to handle them safely. Orcas appear to exploit the same off switch, inverting great whites until they drown. Even apex predators carry a reset button.
Every octopus studied carries a single type of visual pigment, which by the usual definition makes the animal color-blind. Yet octopuses produce camouflage that matches background colors closely enough to fool spectrophotometers. The paradox has been open since the pigment was first measured in 1958.
In the Red Sea, day octopuses hunt alongside goatfish, groupers and other reef fish, and researchers recorded them delivering swift explosive jabs with one arm at particular fish partners. The team called the behavior active displacement. Sometimes it clears a competitor off prey; sometimes there is no prey to grab at all. The scouting fish get punched least, and the loafers get punched most.
Bull sharks regulate the salt in their bodies so well that they thrive in fresh water, and they have been recorded more than 1,600 km (1,000 miles) up the Mississippi — famously near Alton, Illinois, in 1937. Lake Nicaragua's “landlocked” sharks turned out to be ordinary bull sharks: tagging from 1966 to 1972 showed them commuting both ways along the San Juan River from the Caribbean, and they most likely breed at sea. The shark in the river is not a legend.
The argonaut is a small octopus that lives in open water, and the female builds herself a thin white shell using two of her arms. She swims to the surface, traps a gulp of air inside the shell, then dives — and deep down the squeezed air balances her weight exactly, so she floats in midwater without swimming.
The shark lineage has endured for more than 400 million years, swimming through all five of Earth's great mass extinctions — including the one that ended the dinosaurs. They watched the rise and fall of nearly everything else in the ocean.
Sharks are tuned to low-frequency pulses — the irregular vibrations of a struggling fish — which they detect with inner ears and a lateral-line system running the length of the body. Long before a shark sees you, it has heard and felt you.
Octopuses are semelparous: females produce a single clutch, guard it without feeding, and die around the time it hatches. Males typically die not long after mating. The one clear exception found so far, the larger Pacific striped octopus, spawns repeatedly and keeps eating — which is why researchers now study its optic glands looking for what the rest of the order is missing.
Captive octopuses routinely learn to open screw-top containers for food. At the Seattle Aquarium, some also worked out childproof pill-bottle caps. In a baby-bottle test, one octopus bypassed the screw top entirely by tearing off the nipple.
Chromatophores hold only yellow, red, brown and black pigments, so no combination of them can produce the blue-green sheen a living octopus sometimes shows. Two other cell types do that work: iridophores, stacks of protein plates that split light by interference, and leucophores, which scatter whatever light falls on them and so look red in red light and blue in blue. Part of octopus color is not paint at all. It is optics.
Octopus marginatus and Abdopus aculeatus have been filmed walking on two alternating rear arms while wrapping the other six around the body. One resembles a drifting coconut and the other a clump of algae. The behavior was the first documented bipedal locomotion in an animal without a rigid skeleton.
The cookiecutter's lower teeth are fused into a single serrated band that sheds whole, not tooth by tooth — and the shark swallows the discarded band, likely recycling its calcium. It eats pieces of giants, and then it eats its own knives. Nothing in its economy goes to waste.
Shark teeth are not anchored in bone; they sit in the gums on a conveyor of replacements, with new rows rotating forward as old teeth fall away. Some species may cycle through 30,000 or more in a lifetime. Losing a tooth costs a shark about a week, not a dentist.
Octopuses use copper-based hemocyanin instead of iron-based hemoglobin to carry oxygen. Oxygenated hemocyanin is blue and remains effective in cold, oxygen-poor water, although it carries less oxygen per unit of blood than hemoglobin.
Tagged blue sharks ride ocean gyres on migrations spanning thousands of miles — Atlantic individuals recaptured across the ocean from where they were marked — following temperature bands and prey like long-haul truckers of the open sea. Their round trips can circle an entire ocean basin.
Expeditions to Kavachi, an active undersea volcano in the Solomon Islands, filmed hammerheads and silky sharks living inside its acidic, superheated crater plume — a discovery nicknamed "Sharkcano" that NASA later observed erupting from orbit. Some sharks chose the one neighborhood everything else evacuated.
The broadnose sevengill — a stout, spotted cow shark with seven gill slits instead of the usual five, up to about 3 m (10 ft) long — is one of the few sharks that regularly prey on seals, and it does not always do it alone. Off South Africa and California, observers have watched sevengills hunting in loose packs, a strategy David Ebert described in 1991 as social facilitation, alongside stealth, ambush and sudden bursts of speed. Adults have only two known predators of their own: orcas and great whites. A shark shaped like a Jurassic leftover runs the coast like a wolf pack.
Field measurements put the Greenland shark's heart rate near one beat every ten seconds, among the slowest recorded for any fish — machinery throttled down for water near freezing. The same economy drives its glacial growth and centuries-long life. It is an animal living in slow motion.
An Australian aquarium's zebra shark named Leonie reproduced with a mate for years, then — separated from males — produced viable young alone; DNA testing in 2017 ruled out stored sperm and confirmed parthenogenesis. It was the first shark seen switching reproductive modes within one lifetime. She didn't lose the option; she changed the setting.
Flat as a doormat, the angel shark buries itself in sand with only eyes showing and explodes upward in a tenth-of-a-second strike on passing fish. Once common from Norway to the Canaries and across the Mediterranean, it has disappeared from about 90% of that range in a century, was listed Critically Endangered by the IUCN in 2006, and hangs on mainly around the Canary Islands. The floor of the sea sometimes has teeth.
Great white sharks, shortfin makos and their mackerel-shark kin run heat exchangers of tightly packed blood vessels that keep swimming muscles, eyes and brain well above sea temperature — regional warm-bloodedness in a fish. A warm retina sees fast prey in cold water. The great white hunts pre-heated.
A 2009 genetic survey found venom proteins across octopuses, cuttlefish and some squid, tracing them to a single ancient venomous ancestor. Most species use theirs quietly, paralyzing a clam until its shell relaxes open. Only the blue-ringed octopuses of the genus Hapalochlaena carry a toxin dangerous to humans.
Sharks have no gas-filled swim bladder; buoyancy comes from an enormous oil-rich liver that can approach a quarter of a shark's weight in some species. The oil, squalene, is lighter than water, letting a heavy cartilage body hang almost weightless. A shark floats on its own chemistry.
While cousins cross oceans, tracked blacktip reef sharks often spend years inside a home range of well under a square kilometer of reef. The fin cutting the lagoon today is likely the same individual as last season's. Not every shark is a wanderer; some are neighbors.
The Port Jackson shark lays a spiral, corkscrew-shaped egg case that the mother wedges into rock crevices, where the threads lock it against the surge. Beachcombers who find washed-up cases call them mermaid's purses. Evolution invented the screw thread long before people did.
Lacking the swim bladder most fish use to make noise, sharks were long declared voiceless. Then in March 2025 researchers published the first documented shark sounds: rig sharks in New Zealand snapping out 48-millisecond clicks, likely with their flattened teeth, when handled. Five hundred species just became an open question.
Biomechanical modeling published in 2008 estimated the bite force of megalodon, the largest shark that ever lived, at roughly 108,000 to 182,000 newtons — up to about 41,000 pounds of force, the strongest bite calculated for any animal at the time. That is several times the estimated bite of Tyrannosaurus rex. The figure often circulates mislabeled as “psi”; it is total force, and it needed no exaggerating.
Stefano Lorenzini described the jelly-filled snout pores of sharks in 1678, but their electric-sensing purpose was only demonstrated experimentally in the 20th century — three centuries between discovery and explanation. Sometimes science finds the organ long before the sense.
The star-sucker pygmy octopus, Octopus wolfi, lives in the shallow coastal waters of the western Pacific Ocean, measures under 2.5 centimeters (1 inch) in total length and weighs less than a gram (0.04 ounce) — smaller and lighter than a small coin, and small enough to sit on a fingernail. It is named for the ring of tiny papillae fringing the suckers near its arm tips, which let it taste whatever it touches.
Blue-ringed octopus saliva contains tetrodotoxin, a potent neurotoxin with no known antivenom. Symbiotic bacteria in the posterior salivary glands produce the toxin, and females also coat their eggs with it.
When food is thick, a whale shark can hang nearly vertical in the water and gulp — using suction rather than forward motion to draw in prey-rich water. Snorkelers at feeding aggregations often meet the giants bobbing upright like feeding balloons. The largest fish can dine without swimming an inch.
The silky shark's denticles are so small and densely packed that its skin feels sleek rather than sandpapery — the trait that named it. The finish trims drag for a life spent chasing tuna in open water. Even among sharks, there is a best-dressed.
Behind a whale shark's mouth, up to 1.5 m (5 ft) across, the esophagus narrows to a passage only several centimeters (a few inches) wide. Anything oversized gets spat back out.
At the Seattle Aquarium, eight giant Pacific octopuses met two unfamiliar people dressed the same way for two weeks: one always fed them, the other always touched them with a bristly stick. By the end, the animals showed measurably different body patterns, arm movements and funnel orientation toward each person, and the larger ones changed their breathing rate. The uniform trick was the point. They were not reading the clothes.
A blue-ringed octopus is small and usually drab, but vivid iridescent blue rings appear when it feels threatened. The display serves as a warning; the animal generally tries to escape, and nearly every recorded bite has come after someone picked it up.
The deep-sea goblin shark's jaws shoot forward at prey in what researchers measured as the fastest jaw protrusion known in fishes, snapping out from under its blade-like snout before retracting. Video analysis published in 2016 called the mechanism "slingshot feeding." Its face is a loaded weapon.
The great white is stocky, and gets stockier as it grows — which the 2025 megalodon study concluded caps it near 7 m (23 ft), because a bulky body shoves aside too much water to be worth hauling any bigger. Every giant that swims is built long and lean instead: the whale shark, the basking shark, the great whales. The ocean's most feared predator is held back by its own build.
Juvenile zebra sharks wear bold dark-and-pale bands; as they mature the bars dissolve into a field of leopard-like spots, and divers routinely misname the adults. One species manages to impersonate two big cats in one lifetime. The zebra grows up to be a leopard.
Female bull sharks deliver pups in estuaries and river mouths, and the young may spend years in low-salinity nurseries where big marine predators cannot follow. Fresh water is not a stunt for the species; it is a life stage. Some of the ocean's most formidable sharks learned to swim in rivers.
The Greek roots behind Cephalopoda translate as head and foot, describing a body plan in which the two are fused. The eight arms are modifications of the same muscular foot that a snail crawls on, rearranged into a ring around the head. The mouth and beak sit underneath, at the center of that ring. An octopus is a mollusk that walks on a reinvented snail foot.
The animal long called the common octopus, Octopus vulgaris, is now understood as a species complex rather than a single worldwide species. Genetic studies have identified at least six regional species that can be extremely difficult to distinguish by appearance alone.
In April 2019, cameras lowered into the Java Trench during the Five Deeps Expedition recorded a dumbo octopus foraging at 6,957 meters (22,825 feet), in water of about 1.5 °C (35 °F). A second animal turned up at 5,760 meters (18,898 feet). The previous reliable record, a black-and-white photograph, had stood at 5,145 meters for half a century.
Sharks first appeared roughly 450 million years ago. Trees — with their distinctive woody trunks and deep root systems — only evolved about 350 million years ago. The predators had a 100-million-year head start.
The whale shark is the largest fish alive, and the biggest reliably measured individual reached 18.8 m (61 ft 8 in). It feeds almost entirely on plankton, straining tiny drifting life through a mouth up to 1.5 m (5 ft) wide. The ocean's biggest shark eats some of its smallest creatures.
At the base of Davidson Seamount off California, about 3,200 meters (10,500 feet) down, roughly 6,000 nesting pearl octopuses were counted in a 2.5-hectare patch, and researchers estimate the full site holds more than 20,000 nests. Named the Octopus Garden, it is the largest octopus aggregation known anywhere. The animals migrate there to mate, nest and die.
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