Whale shark reproduction was a mystery until 1995, when a female landed in Taiwan — nicknamed “megamamma” — held about 300 embryos at different stages, proving the species bears live young from egg cases hatched internally. At roughly 300, the litter was more than double the largest recorded for any other shark, the blue shark's, at around 135. The biggest fish is also the biggest maternity ward.
White sharks lack the protective third eyelid many sharks deploy, so in the last instant of a strike they rotate each eye backward in its socket, exposing tough white tissue. The predator goes momentarily blind precisely when a seal's claws are closest. It trades sight for eyes it can keep.
During more than 500 diver hours off Indonesia, researchers watched veined octopuses dig up coconut-shell halves, stack them and carry them as far as 20 meters (66 feet) before assembling them into shelters. Because the shells provide no protection while being transported and are saved for later use, the behavior was classified as tool use.
A white shark tagged in South Africa — nicknamed Nicole — swam to Australia and back, about 20,000 km (12,400 miles) round trip in under nine months, the fastest transoceanic return migration then recorded for a marine animal. She navigated with no coastline for weeks at a stretch.
Dried, untanned shark skin — shagreen, usually from small sharks called dogfish — is a natural abrasive: its denticles cut like 80- to 220-grit paper in one direction and burnish in the other, and cabinetmakers and instrument makers smoothed wood with it for centuries; a microscope study of a 1711 Stradivari cello found what looks like a dogfish denticle lodged in the varnish. Tanned and dyed, shagreen also covered cases, boxes and sword grips. The famous exception is the samurai sword: its hilt covering is called samegawa, “shark skin,” but the museum pieces are wrapped in ray skin. On the katana the shark got the name and the ray did the work.
Shark young are pups, and in nearly all species they are born fully armed and immediately abandoned; nursery lagoons, not mothers, keep them alive through their first years. A newborn lemon shark's first lesson is that no one is coming.
Every whale shark wears a unique constellation of pale spots, so scientists adapted a 1986 star-mapping algorithm built for the Hubble Space Telescope era to match shark flanks the way astronomers match star fields. The method anchors a global photo-ID library with tens of thousands of encounters. Fittingly, the whale shark's name in Madagascar — marokintana — means "many stars."
A giant Pacific octopus has roughly 200 to 250 suckers on each arm. Monterey Bay Aquarium reports up to 2,240 suckers in a female, about 100 more than in a male. Each sucker can grip independently, and those near the arm tips are the smallest and most sensitive.
A great white breathes only by moving: it swims with its mouth open so water washes over its gills, and if it stops, it suffocates. Makos are built the same way. Most sharks are not — they can pump water across their gills while resting, which is how a nurse shark sleeps motionless on the bottom. “All sharks die if they stop swimming” is folklore with a grain of truth stretched over 500 species.
Juvenile scalloped hammerheads cruising sun-drenched shallows darken dramatically as melanin builds in their skin — one of the first demonstrations of true sunlight-driven tanning in a fish, published in Nature in 1996. Sharks kept shaded stayed pale while sunlit sharks browned. The beach tan predates the beach towel by millions of years.
A whale shark's back is covered in some of the thickest skin in the animal kingdom — up to about 10 cm (4 in) — and it hardens the surface further by flexing when boats or predators come close. The gentlest giant wears the heaviest coat.
Three-dimensional tracking of octopus-fish hunting groups showed goatfish scouting ahead and signaling discoveries, while the octopus largely determined whether the group moved toward them. Group composition also changed how much each species contributed and how successful the hunt was.
The salmon shark's heart is loaded with SERCA2, a calcium-pump protein expressed at levels closer to a mammal's heart than a fish's, keeping cardiac muscle contracting in water that would stop most fish hearts. The finding, published in Science in 2005, helped explain how a warm-bodied shark patrols sub-Arctic seas. Its cold tolerance is written in molecules.
The pale deep-sea octopod nicknamed Casper was filmed near Hawaii in 2016 at more than 4,000 meters (13,100 feet) — the deepest record was 4,290 meters (14,100 feet) — a record depth for its group. Related octopods were then found attaching their eggs to the stalks of dead sponges, and those sponges grow only on manganese nodules — potato-shaped metal lumps that take millions of years to form and are prime targets for seabed mining. Remove the nodules and the sponges go, and with them the nursery.
When basking shark carcasses decay, the gill apparatus and lower jaw fall away first, leaving a small-headed, long-necked hulk — the source of several famous "sea serpent" and "plesiosaur" strandings, including the 1977 Zuiyo-maru carcass hauled up off New Zealand. Many monsters, examined closely, turn out to be sharks twice over.
At the Octopus Garden, a nursery near the base of Davidson Seamount off California, surrounding seawater is about 1.6 °C (35 °F), while water seeping from cracks reaches nearly 11 °C (51 °F). Pearl octopus (Muusoctopus robustus) mothers cement their eggs to the rock and brood in the warmer crevices, where higher temperatures raise metabolic rates and shorten incubation from an expected five or more years to roughly 1.8 years.
A resting octopus lies pale and still, then erupts for about a minute into twitching arms, darting eyes, quickened breathing and racing skin patterns before going quiet again. The phase has a raised arousal threshold, is regulated by prior sleep, and produces neural activity resembling wakefulness, making it broadly comparable to mammalian REM sleep.
The megamouth shark — a blubbery, 16-foot (5 m) filter feeder with a cavernous, glow-lipped mouth — was entirely unknown until one tangled in a U.S. Navy vessel's gear off Hawaii in 1976. Only a few hundred sightings have ever been logged since. The 20th century's biggest zoological surprise swam in from the deep.
Researchers measuring shark bites found the bull shark delivering nearly 6,000 newtons (about 1,300 pounds of force) at the back teeth — the strongest bite for body size of any shark tested, published in 2012. The stout jaw is built like a bolt cutter for turtles and big fish. Size sets the headline; the bull shark sets the ratio.
Octopus photoreceptors are arranged in two channels that detect the orientation of polarized light. Behavioral tests show they can distinguish differences in polarization angle of only a few degrees. This can make transparent prey visible even when brightness and color provide little contrast.
The English had sea dog, dogfish and hound-fish — names for the small sharks of home waters — but no name at all for the big tropical animal Captain John Hawkins's men brought to London in 1569. A handbill advertising the specimen said exactly that: there was no proper name for it, “but that certayne men of Captayne Haukinses doth call it a sharke.” Within thirty years “shark” also meant a swindler, and etymologists still argue which sense came first.
Repeated behavioral tests have found consistent individual differences in octopus activity, reactivity and avoidance. Later work in another species found similar temperament differences early in life, showing that individuals of the same species can behave predictably differently.
The central brain is not a lump above the mouth. It is a donut of fused lobes encircling the esophagus, split into a supraesophageal mass handling learning and memory and a subesophageal mass handling movement. Food passes through the middle of the brain on its way to the gut. Whatever an octopus swallows, it swallows through its own head.
The great white shark gives more of its brain to smell than any other shark: its olfactory bulbs — the paired lobes that process scent — run to about 18% of its brain mass.
The eel-like frilled shark, a deep-water relic with 300 needle teeth arranged in frills, is estimated to carry its young for around 3.5 years — among the longest gestations proposed for any vertebrate. In the cold deep, even birth runs in slow motion.
The bluntnose sixgill belongs to the Hexanchiformes, the oldest-known group of modern sharks, already swimming by the Early Jurassic about 195 million years ago — before most dinosaurs, though not before the first. It keeps six gill slits where nearly every other living shark has five, and patrols deep water worldwide, rising toward the surface at night. Meeting one is the closest thing to diving with the Jurassic.
With no internal or external skeleton, an octopus is roughly 90% muscle. Its arms act as muscular hydrostats, stiffening, bending and extending by contracting muscles against one another rather than pulling on bones. This structure gives the animal both strength and extreme flexibility.
For centuries Europeans prized glossopetrae — "tongue stones" — as magical charms against poison, believing they fell from the sky or grew from serpents' tongues. In 1666 the Danish anatomist Nicolas Steno dissected a great white shark's head and showed they were shark teeth, a founding moment for paleontology. A superstition dissolved in one dissection.
The epaulette shark of Australian reefs walks across exposed coral flats on its paddle-shaped fins, wriggling between tide pools. It survives the trip by tolerating extreme oxygen loss that would injure most vertebrates, shutting down non-essential brain functions until it reaches water. It is a fish that hikes between puddles.
Sawsharks wield flattened, tooth-edged snouts hung with a pair of trailing barbels, slashing through fish schools and raking sand for buried prey — unlike the larger sawfish (a ray) they resemble. It is a weapon, a metal detector and a shovel in one nose.
Sharks retain urea and other compounds in their blood until their body fluids match or exceed seawater's concentration, so they never dehydrate in the ocean the way bony fish do. It is also why poorly handled shark meat reeks of ammonia. Sharks solved seawater chemistry from the inside.
Great white sharks refuse captivity: they ram tank walls and stop eating, and open-ocean hunters that travel hundreds of miles do not settle in a box. The exception was a juvenile female at the Monterey Bay Aquarium, held 198 days in a 4.5-million-liter (1.2-million-gallon) tank from September 2004 to March 2005 and seen by more than a million visitors before she killed two tankmates and was released. Five more juveniles followed, for 11 days to five months, until the program ended in 2011 when the last died days after release; an adult netted by a Japanese aquarium in 2016 refused food and died in three days. Some apex predators cannot be exhibited — only visited.
Researcher Jennifer Mather observed a wild octopus leave its den, collect three rocks, set them aside, carry them back and stack them across the entrance before resting. The sequence has been discussed as possible planning, although that interpretation remains debated.
Satellite-tagged whale sharks travel thousands of kilometers to arrive precisely when food blooms — coral spawn off Australia, fish eggs off Yucatán — forming seasonal gatherings of hundreds, the largest known assemblies of giant fish. Somehow, the world's biggest fish keeps a calendar.
The California two-spot octopus has a genome about 2.7 billion DNA base pairs long, slightly smaller than ours. Yet researchers identified about 33,600 protein-coding genes, compared with roughly 20,000 in humans. Surprisingly, this extra genetic complexity did not come from duplicating the entire genome; instead, certain gene families expanded and the genome was extensively rearranged.
Venus turns so slowly that a single rotation takes 243 Earth days, while its whole trip around the Sun takes only 225. On Venus, the day outlasts the year.
Octopuses drag prey home and discard the shells outside the entrance, building a heap called a midden. Divers use these piles of cracked crab and clam shells to locate dens that would otherwise be invisible. The habit is old enough that Aristotle noted it more than 2,000 years ago.
When an octopus cannot pull a shell open, a muscular salivary papilla studded with minute teeth — separate from the radula, its primary toothed ribbon — can drill through it. Secretions from the posterior salivary glands then help relax the muscle holding the shell closed.
Greenland shark stomachs have yielded remains of seals, reindeer and even polar bear, though the sluggish sharks are believed to scavenge much of it and ambush sleeping seals for the rest. In the Arctic food web, the slowest fish still collects the largest tolls.
In 2016 staff at the National Aquarium of New Zealand in Napier found Inky's tank empty and a trail of water across the floor. He had exploited a lid left ajar after maintenance, crossed roughly 2.5 meters (8 feet) of floor and squeezed into a drainpipe about 50 meters (160 feet) long that emptied into Hawke's Bay. He was never seen again. His tankmate, Blotchy, stayed put.
Field studies of reef sharks document deep bite wounds closing within weeks and even severe fin damage regenerating, with infection strikingly rare in bacteria-rich water. Antimicrobial skin chemistry and fast tissue repair appear to do the work. Researchers study shark healing hoping some of it can be borrowed.
Many large sharks mature astonishingly late — white sharks at roughly 26–33 years by vertebral studies, Greenland sharks near 150 — and then produce few young after long pregnancies. That slow arithmetic is why overfishing empties shark seas so fast and refills them so slowly.
Voluntary arm shedding, or autotomy, has been documented in at least Abdopus aculeatus and Ameloctopus litoralis. The arm separates at a defined break point and continues writhing while the octopus escapes.
Archaeologists have opened Egyptian tombs and found pots of honey more than 3,000 years old — still perfectly edible. With almost no moisture, heavy sugar and a naturally acidic pH, honey is a pantry where bacteria simply cannot live.
The International Shark Attack File puts a U.S. beachgoer's lifetime-scale risk of a fatal shark bite near one in 4.3 million — far below the risks of lightning, bees or the drive to the beach. In a typical year sharks bite about 70 people worldwide, unprovoked, and about six of those bites are fatal.
The salmon shark of the North Pacific maintains body temperatures around 21–26 °C (70–79 °F) even in near-freezing water — among the warmest bodies of any fish — letting it chase salmon where most predators stiffen. It is a shark wearing its own wetsuit of blood.
A whale shark's cavernous mouth carries about 300 rows of tiny vestigial teeth — thousands in all — that play no role in feeding, leftovers from toothier ancestors; the animal filter-feeds instead through gill rakers. Evolution rarely cleans out the attic.
The 20-inch (50 cm) cookiecutter shark twists out neat round plugs of flesh from tuna, whales and great whites — and its bites have damaged the rubber sonar domes of U.S. Navy submarines. Its Latin name, Isistius brasiliensis, honors an Egyptian goddess of light, for the glow along its belly. Few animals so small have scarred so many giants.
A shark's skin is armored with tooth-like denticles whose ridges shed drag, and engineers have been copying them. In 2014 a Harvard team 3D-printed an artificial shark skin and showed it improved swimming performance on a flapping foil; in 2018 the same lab, with the University of South Carolina, molded shortfin mako denticles onto an airfoil and found arrangements that cut drag and added lift at once, improving the lift-to-drag ratio by up to 323% at low angles of attack. Denticle-patterned surfaces are studied for aircraft, drones and wind turbines. Four hundred million years of prototyping ended up in engineering journals.
By 2020, pocket sharks were known from exactly two specimens: a 40 cm (16 in) female trawled near the Nazca Ridge off Chile in 1979, and a 14 cm (5.5 in) male netted in the Gulf of Mexico in 2010 and named the American pocket shark in 2019. Each carries a slit-like pocket above the base of each pectoral fin, and a 2020 study of the Gulf specimen's pocket glands found the cellular machinery for secreting a luminous fluid. A shark barely longer than a smartphone is built with glowing pockets.
To purge something indigestible, a shark can perform gastric eversion — pushing its whole stomach out through its mouth, rinsing it inside-out in seawater, then swallowing it back into place. Scientists have filmed the maneuver taking only seconds. It is the ocean's most extreme reset button.
The thresher's scythe-like upper tail can equal the length of its body, and high-speed video published in 2013 shows the shark whipping it overhead to stun whole groups of sardines before circling back to swallow the dazed. It is the only shark that hunts with a bullwhip.
When the Moon formed about 4.5 billion years ago, the young Earth spun so fast that a full day lasted only around six hours. The Moon's tides have been braking the planet ever since — for about a billion years in the middle, the day even stalled near 19 hours while sun-driven tides in the atmosphere pushed back. Today the day is still stretching, by about two milliseconds every century.
CT scans published in 2021 revealed that the spiral intestine of sharks functions like a Tesla valve, easing food one way while resisting backflow — a design engineers patented a century after sharks evolved it. Digestion, in a shark, is plumbing genius.
Off South Africa, a pair of orcas has repeatedly killed great white sharks and removed their energy-rich livers with almost surgical precision, leaving the rest. Tagging studies show white sharks fleeing the region for months after such attacks. The ocean's most feared fish has a boss.
Jaws (1975) invented the modern summer blockbuster — wide release, saturation advertising, the first film past $100 million at the U.S. box office — and fixed the shark in the public mind as a man-hunting monster. Author Peter Benchley spent his later life publicly regretting the panic and campaigning for shark conservation. One fictional shark changed how a planet saw real ones.
Juvenile lemon sharks in Bimini prefer specific companions and learn tasks faster after watching experienced sharks — evidence of social personality and social learning in a fish long assumed solitary and simple. Shark school is not just a pun.
In a 2021 experiment, 20 wild-caught bonnethead sharks held in a tank were exposed to magnetic fields mimicking spots hundreds of kilometers (hundreds of miles) from where they were caught — and turned to swim “home,” orienting on magnetic cues alone, the first solid evidence that sharks read Earth's magnetic field as a true map. Some of the longest migrations in the sea may run on planetary GPS.
Unlike whale sharks, which gulp and suction-feed, the basking shark is a pure ram filter feeder: its colossal gape works only when the animal swims forward, forcing water through its gill rakers. Stop the shark and the filter stops with it. For a basking shark, motion is the meal.
Hundreds of suckers per arm will stick to almost anything they meet, which raises an obvious problem for an animal with eight boneless arms. Israeli researchers found that amputated octopus arms grabbed petri dishes readily but would not grab octopus skin, and gripped dishes smeared with skin extract about ten times more weakly. The signal works in the arm itself, with no help from the brain. The octopus solved knots with chemistry.
Bamboo shark embryos, still sealed in their egg cases, freeze — stopping gill movement — when they detect the electric field of a predator outside, resuming only when the threat passes. The survival course begins before hatching.
The myth that sharks are cancer-proof — spread by a 1990s book and a cartilage-pill industry — is false: scientists have documented tumors in dozens of shark and relative species, including a large tumor on a great white shark's jaw reported in 2013. The legend sold supplements; the biology never cooperated.
The giant Pacific octopus (Enteroctopus dofleini) can span about 4.3 meters (14 feet) from arm to arm. The heaviest individual reliably weighed alive was 71 kilograms (156 pounds), while most adults are far smaller.
Heat swells the tower's 7,300 metric tons of iron, lifting it as much as 15 centimeters (6 inches) taller in high summer than in deep winter, by engineers' estimates. And because the sun warms one face faster than the rest, over a clear day the summit traces a little circle about 15 centimeters wide — always leaning gently away from the sun.
Harvard researchers identified a family of chemotactile receptors found only in cephalopods and expressed in the suction cups themselves. They detect molecules that dissolve poorly in water — exactly the compounds that would cling to a crab's surface rather than drift away. So an octopus probing a dark crevice is not groping blindly. Each sucker is reporting flavor.
The basking shark, the second-largest fish, cruises open-mouthed and passively strains plankton from roughly 1,800 metric tons of seawater per hour — on the order of an Olympic pool's worth. All that machinery runs on animals barely visible to the eye.
Portuguese dogfish have been recorded around 3,700 m (12,100 ft) deep — among the deepest confirmed for any shark — hunting in freezing blackness at pressures hundreds of times the surface's. Even the abyss has its patrols.
Sharks of all species combined kill people in the single digits in a typical year — the International Shark Attack File's recent five-year average is eight unprovoked deaths worldwide — while mosquito-borne diseases kill hundreds of thousands, malaria alone about 600,000. In the coastal United States, lightning kills roughly 38 people a year to sharks' one every other year, and dogs about 35. Fear tracks teeth, not numbers.
Female common blanket octopuses reach about 2 meters (6.5 feet) long, while males top out near 2.4 centimeters (1 inch). The weight ratio is at least 10,000-to-1 and may reach 40,000-to-1, among the most extreme size gaps known in any large animal. Males are so rarely encountered that the first live one was not photographed until 2002, off the Great Barrier Reef.
In trials with eight giant Pacific octopuses, two repeatedly jetted water at a floating pill bottle so a tank current carried it back, then jetted it away again. Researchers classified the repeated, non-feeding behavior as exploratory play. Later studies found similar play with other objects and in adults as well as juveniles.
Octopuses retune their nervous systems with the seasons: they can extensively edit their RNA, altering the proteins produced from the same genes. When California two-spot octopuses were acclimated to 13 °C (55 °F) instead of 22 °C (72 °F), editing changed at more than 20,000 sites, including sites in proteins involved in nerve signaling and intracellular transport.
Radiocarbon dating of proteins in their eye lenses shows Greenland sharks live at least 272 years — longer than any other animal with a backbone. The oldest of the 28 sharks measured in the landmark 2016 study, a female just over 5 m (16 ft) long, was estimated at roughly 392 years old. Females don't even reach maturity until around 150, and a big one cruising the Arctic today has been swimming for some three centuries.
On Great Barrier Reef platforms cut off at night by spring low tides, the epaulette shark tolerates hours of severe hypoxia — oxygen near 5% of normal — and at least an hour of total anoxia, with no drop in its brain's energy stores and no neurons lost afterward. It manages this by throttling demand rather than boosting supply: an adenosine-driven slowdown leaves the shark in a coma-like torpor until oxygen returns, when it snaps back to alertness within moments. Researchers at Griffith University and the University of Auckland study its brain mitochondria for clues to limiting stroke and heart-attack damage, where the harm comes as oxygen floods back. A reef shark's hour without oxygen is a lesson medicine wants.
Behind a shark's retina lies the tapetum lucidum, a layer of mirror-like plates that bounces unabsorbed light back through the photoreceptors for a second pass. The same structure makes a cat's eyes shine in headlights. In dim water, a shark's eye reads every photon twice.
Megalodon, the extinct giant that grew several times the size of any shark alive, left teeth so like a great white shark's that the family tree looks obvious — but fossil evidence places the two on separate lineages, the white shark's ancestry tracking closer to ancient mako-like sharks. Megalodon's line ended; it left no descendants. The great white is the giant's rival's grandchild, not the giant's.
Pairs of larger Pacific striped octopuses mate face to face with their suckers aligned, share food and may occupy the same den for days. Females produce multiple clutches over months instead of a single terminal brood.
Cirrate octopuses, the deep-sea group nicknamed dumbo for the ear-like fins above their eyes, propel themselves by slowly beating those fins rather than by jetting water. A web of skin joins the arms into an umbrella. The deepest octopus ever filmed was one of them, foraging almost 7 kilometers down.
Sand tiger shark embryos hatch inside their mother and the largest in each uterus devours its smaller siblings, a behavior called intrauterine cannibalism. Each of the two uteri ultimately delivers a single battle-tested pup. The nursery is the first hunting ground.
An octopus has one brain, but a highly distributed nervous system. The central brain in its head does the learning, the remembering and the deciding, while each of the eight arms carries its own large cluster of neurons that can sense touch and taste and control much of the arm's movement without waiting for orders. Those clusters are nicknamed mini-brains, but nothing in an arm learns or remembers.
Given eight seemingly interchangeable arms, an octopus still plays favorites: in a 2006 experiment, every animal tested reached into a maze with the same preferred arm again and again, and individuals favor one eye as well. Unlike human handedness, though, the species has no side — roughly half the animals lean left and half lean right, so the preference is personal rather than built into the octopus.
The bold dark bars that name the tiger shark belong mostly to youth: they fade as the shark matures, leaving big adults far plainer than their portrait. The name records the juvenile. By the time a tiger shark is truly formidable, it has nearly erased its tiger.
The parrot-like beak is the only hard part of an octopus; everything else is muscle and skin that can be poured through a gap. The Alaska Department of Fish and Game estimates that a 23-kilogram (50-pound) giant Pacific octopus can pass through a hole about 5 centimeters (2 inches) across. One researcher watched an octopus of that size cross a research vessel's deck, find the scupper drain and be gone inside a minute.
Fossil sites in Panama, Spain and the southeastern U.S. preserve concentrations of small juvenile teeth of megalodon, the extinct giant shark that hunted the oceans until about 3.6 million years ago — evidence the giants birthed and raised young in warm, food-rich shallows; 2025 growth analyses indicate newborns already stretched about 3.6–3.9 m (12–13 ft). The deadliest daycare in history had ocean views.
Cornered, the swell shark gulps water to double its girth and wedge itself into rock crevices; under blue light its skin also fluoresces brilliant green, visible to other swell sharks' eyes. It is both a pufferfish impersonator and a secret neon sign.
In 2020 researchers reported that whale shark eyes are covered with more than 3,000 minute dermal denticles — the tooth-like scales that armor shark skin — apparently protecting eyes that have no lids. As a second defense, the shark can retract each eyeball deep into its socket. Even its stare wears chain mail.
The shortfin mako carries its Māori name into science and sport worldwide; in New Zealand tradition mako teeth were treasured ear pendants of high status. One of the ocean's fastest animals is one of the few whose everyday English name is borrowed from a Polynesian language.
The hammerhead's wide-set eyes give it a panoramic view and, when it sweeps its head, effectively 360-degree vision — a 2009 study also confirmed excellent stereo depth perception from the exaggerated eye separation. The strangest head in the sea turns out to be a surveying instrument.
Shark jaws hang in slings of muscle and ligament, letting the whole apparatus thrust forward and gape wide independent of the head — the mechanism behind slow-motion footage of white sharks seeming to launch their mouths at prey. The skull aims; the jaw travels.
From 2007 to 2011, researchers from the Monterey Bay Aquarium Research Institute returned 18 times to the same site in Monterey Canyon and found the same scarred Graneledone boreopacifica female guarding about 160 eggs. She was never observed feeding and grew progressively thinner. Her 53-month brood remains the longest recorded for any animal.
Tagged white sharks from California converge each year on a remote mid-Pacific region with little obvious food — nicknamed the White Shark Café — where they dive hundreds of times a day; a 2018 expedition found hidden layers of prey and possible mating behavior. Half the mystery is solved; the reservation system is not.
Octopuses is the standard English plural. Octopi is also widely used, but it applies a Latin-style ending to a word derived from Greek. Octopodes follows the Greek plural pattern. Major dictionaries record all three forms.
Cameras trained on gloomy octopuses in Jervis Bay, Australia, caught 102 throws in 24 hours of footage from a group of about ten animals. Each throw involves gathering silt, shells or algae in the arms and repositioning the siphon under the arm web to blast the material several body lengths. Throws in social contexts were more forceful, more often silt than shells, and more often made by dark-colored individuals — and they frequently connected. Targeted throwing had previously been seen only in some social mammals.
The white shark's two-tone paint job is engineering: slate-gray above blends into deep water for eyes looking down, while the pale belly dissolves into surface glare for eyes looking up. The scheme, countershading, hides a two-ton predator in open water. The most famous silhouette in the sea is built to have none.
Of 500-plus shark species, exactly three became filter-feeding giants — the whale shark, the basking shark and the megamouth — each evolving the strategy separately. Gigantism in sharks arrived not with bigger prey but with smaller. The three largest mouths in the family eat things you can barely see.
The most rigorous global estimate, published in Science in 2024, found fishing kills roughly 80 million sharks annually — about 25 million of them from threatened species — and the toll rose even as anti-finning laws increased tenfold. Sharks, by comparison, kill about six people worldwide in a typical year. For every human lost to a shark, humans take more than 10 million sharks.
Researchers at UC Santa Barbara shone light on isolated patches of skin from the California two-spot octopus and watched the color-changing chromatophores expand, then relax in darkness. The tissue responded fastest to blue light near 480 nanometers, the same wavelength the eye's pigment favors, and the skin turned out to express rhodopsin. They named the effect light-activated chromatophore expansion. The skin does not form images — but it knows when the lights change.
Greenland shark meat is loaded with trimethylamine oxide and urea, enough to sicken anyone who eats it fresh. Icelanders ferment and air-dry it for months into hákarl, a pungent national delicacy served in small cubes. The world's longest-lived vertebrate is also one of its most acquired tastes.
A shark's skin is armored with millions of tiny tooth-like scales called dermal denticles — complete with enamel-like coating, dentine and pulp. The denticles channel water to cut drag, a design so effective that competitive swimsuits mimicking it preceded the 2010 ban on high-tech racing suits. Stroke a shark tail-to-head and it feels like sandpaper.
In round-the-clock observations at 22 °C (72 °F), nocturnal octopuses averaged about 12 quiet-sleep bouts of 50 minutes each plus roughly 10 brief active-sleep bouts. Together, these amounted to about 10 hours of sleep per day. Warmer water shortened the interval between active bouts.
A giant Pacific octopus can grow to tens of kilograms, but a hatchling weighs only about 22 milligrams and is roughly the size of a rice grain. The young drift near the surface as plankton for weeks or months before settling to the seafloor, and only about one in a hundred survives that stage.
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