The Deep Sea
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50 free The Deep Sea trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Most of the living space on Earth lies in cold, dark water that sunlight never reaches. Down there, animals make their own light, food drifts down from far above, and the pressure would flatten an unprotected visitor. It is the largest habitat on the planet and still one of the least explored. This quiz covers the deep sea from top to bottom: the layers of the ocean and how they got their names, the strange fish, cephalopods and worms that live in them, the hot springs and seeps where life runs on chemistry instead of sunshine, and the handful of people and machines that have made the trip down. It is written for curious players, students of marine biology and anyone who has ever stared at a photo of a deep-sea creature and wondered what on earth it was. Every question comes with a short explanation, so you will surface knowing more than when you dived in.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which film director piloted a submersible alone to the bottom of the Challenger Deep in March 2012?
James Cameron
James Cameron made the dive in the Australian-built Deepsea Challenger, sinking for more than two and a half hours to reach the seabed.
Q 02Which deep-sea fish lures prey with a glowing bait that dangles from a modified fin spine on its head?
Anglerfish
Anglerfish light their lure with colonies of glowing bacteria, and their jaws and stomachs stretch to swallow prey up to twice their own size.
Q 03Which crescent-shaped Pacific feature contains the Challenger Deep, the deepest known point in any ocean?
Mariana Trench
The Mariana Trench plunges almost 11 km, so its floor lies farther below sea level than the summit of Everest stands above it.
Q 04Which sea monster of Norwegian sailors' lore is thought to have been inspired by sightings of giant squid?
Kraken
The Kraken was first described in a Norwegian glossary of 1646, and the giant squid that may lie behind the tales can grow more than 10 metres long.
Q 05Which fish from deep waters off Australia was voted mascot of the Ugly Animal Preservation Society?
Blobfish
The blobfish floats just above the seabed without swimming, because its jelly-like flesh is slightly less dense than water.
Q 06What name do scientists give the steady shower of organic debris that sinks into the deep ocean?
Marine snow
Marine snow carries energy down from the sunlit surface, and many animals of the dark water below depend on it for food.
Q 07Which deep-sea cephalopod, the only living member of its order, is named for its dark, cloak-like webbed arms?
Vampire squid
The vampire squid drinks no blood: it feeds on drifting detritus, and its closest living relatives are the octopuses.
Q 08Which deep-diving mammal plunges more than two kilometres to hunt squid and makes the loudest sound of any animal?
Sperm whale
The sperm whale often carries white scars thought to come from fights with giant squid, though no human has ever watched such a battle.
Q 09Which oceanographer co-led the 1985 French-American expedition that found the wreck of the Titanic?
Robert Ballard
Robert Ballard was given the ship time only after he had first surveyed two sunken nuclear submarines in secret for the US Navy.
Q 10Which deep-sea cephalopod, found even in ocean trenches, swims by flapping a pair of fins on its mantle?
Dumbo octopus
The Dumbo octopus is named after Disney's flying elephant and, unlike most of its relatives, has no ink sac to squirt.
Q 11Which lobe-finned fish, thought extinct for about 66 million years, was caught alive off South Africa in 1938?
Coelacanth
The coelacanth is more closely related to lungfish and four-limbed land animals than to ordinary ray-finned fish.
Q 12Bacteria at hydrothermal vents make food using energy from hydrogen sulfide instead of sunlight, in what process?
Chemosynthesis
Chemosynthesis was named by Wilhelm Pfeffer in 1897, eighty years before whole animal communities built on it were found on the seabed.
Q 13The deepest ocean zone, found mainly in trenches below 6,000 metres, takes its name from which Greek god?
Hades
Hades ruled the underworld, and the hadal zone named for him covers under a quarter of one percent of the seafloor yet spans over 40% of the ocean's depth range.
Q 21Hydrothermal vents teeming with life were first found in 1977 on a rift named after which Pacific archipelago?
Galápagos Islands
Near the Galápagos Islands, a geological expedition looking for warm seabed springs stumbled on dense animal communities that nobody had predicted.
Q 22What name is given to seabed vent chimneys that pour out clouds of sulfide minerals in superheated water?
Black smokers
Black smokers were first found in 1979 on the East Pacific Rise, and each chimney starts to grow when the mineral anhydrite settles around a vent.
Q 23Which deep-sea fish looks upward through a transparent, fluid-filled dome on its head?
Barreleye
Q 14What nickname is given to the ocean's mesopelagic layer, where the last faint daylight fades below about 200 metres?
Twilight zone
The twilight zone begins where only 1% of surface light survives, and its base holds the SOFAR channel, the layer where sound travels slowest.
Q 15Which colour of light do most glowing sea animals produce, though a few deep-sea dragonfish also shine red?
Blue
Blue light carries well through seawater while red fades fast, so a dragonfish's red beam is short-ranged but invisible to most of its prey.
Q 16Which Southern Ocean mollusc is the heaviest invertebrate known and has the largest eyes of any animal?
Colossal squid
The colossal squid can weigh about half a tonne, and it is the only member of its family armed with hooks on its arms and tentacles.
Q 17Which deep-sea crustacean, a relative of the garden woodlouse, can grow as long as 50 centimetres?
Giant isopod
The giant isopod is built for famine: captive animals have survived more than five years without food.
Q 18In which bathyscaphe did Jacques Piccard and Don Walsh first reach the Challenger Deep in 1960?
Trieste
Trieste was Swiss-designed and Italian-built, and it floated on tanks of petrol, a liquid that is lighter than water and barely compresses.
Q 19Which hydrothermal vent animal has no mouth or gut and lives on food made by bacteria inside its body?
Giant tube worm
The giant tube worm is also the fastest-growing invertebrate known in the sea, able to colonise a new vent and reach maturity in under two years.
Q 20Which Woods Hole submersible located a lost hydrogen bomb off Spain in 1966 and later explored the Titanic?
Alvin
Alvin has made more than 5,000 dives since 1964, even though it once flooded and sank in 1,500 metres of Atlantic water.
The barreleye was long thought to have eyes fixed in place, until researchers in 2008 found that they can rotate forward to track prey.
Q 24Which deep-sea eel, also known as the gulper, has a loosely hinged mouth far larger than its own body?
Pelican eel
The pelican eel can open its jaws wide enough to swallow a fish much larger than itself, and it was first watched alive in the wild only in 2018.
Q 25Which small deep-sea fish needs sockets beside its brain to hold the tips of its two longest lower teeth?
Fangtooth
The fangtooth looks fearsome but is harmless to humans, and its family holds just two species with no known close relatives.
Q 26Osedax worms, first found in Monterey Bay in 2002, feed by boring into which part of dead whales on the seabed?
Bones
Bones give the genus its Latin name, which means 'bone devourer', and its females are more than 20,000 times larger than the males.
Q 27Which kind of fish has been filmed swimming more than 8,300 metres down in the Pacific's Izu–Ogasawara Trench?
Snailfish
Snailfish reach the surface intact when hauled up from such depths because, unlike many fish, they have no swim bladder.
Q 28Which tiny deep-sea fish, notably the genus Cyclothone, are thought to be Earth's most abundant vertebrates?
Bristlemouths
Bristlemouths are named for their odd, bristle-like teeth and are estimated to number in the trillions or even quadrillions.
Q 29The sea pig, which roams abyssal plains on enlarged tube feet, belongs to which group of echinoderms?
Sea cucumbers
Sea cucumbers of this genus use their tube feet to gather organic matter that has settled on the seabed, churning up the mud as they feed.
Q 30Which ribbon-shaped fish, the world's longest bony fish, may be the source of many old sea serpent sightings?
Giant oarfish
The giant oarfish can reach about 8 metres, and its common name probably comes from its long, oar-shaped pelvic fins.