15 questions on the inhabitants of our oceans: sharks, octopuses, whales, seahorses, giant squid and living fossils. The ocean is stranger than you think.
The ocean covers 71% of Earth and remains largely unexplored. This quiz tests what you know about its most fascinating inhabitants, from the most fearsome to the most bizarre.
Pick your level
The ocean holds biological records with no equivalent on land: the largest animal ever (the blue whale), the largest eyes in the animal kingdom (the giant and colossal squids), species that change sex, others that have not evolved in 400 million years. This quiz explores the biggest surprises.
If this quiz has made you curious about the wider animal kingdom, the Animal Kingdom Quiz covers fauna from around the world, and the Space & Astronomy Quiz takes you even further into the mysteries of the universe.
All ten easy level questions, with the answer and the reasoning behind it.
Correct answer: Emperor penguin
The emperor penguin, at up to around 1.2 metres.
Correct answer: A pod
A pod, and they are very chatty.
Correct answer: Gills
Gills, which take oxygen out of the water.
Correct answer: A blue tang
A blue tang, if she can remember it herself.
Correct answer: An empty shell
An empty shell, and it moves to a bigger one as it grows.
Correct answer: Orca
Orca, and it is actually a very large dolphin.
Correct answer: 10
Ten, which makes it a decapod, like lobsters and prawns.
Correct answer: Cartilage
Cartilage, the same flexible material as your nose and ears.
Correct answer: Rocks
Rocks, often balanced on their chests as they float on their backs.
Correct answer: Sawfish
The sawfish, which uses it to sense and slash its prey.
Want to warm up before playing or double-check something? Open any question to reveal the correct answer and a short explanation.
Correct answer: Whale shark
The whale shark (Rhincodon typus) can reach 12 to 18 metres in length and weigh up to 21 tonnes. Despite its imposing size, it is a completely peaceful animal that feeds on plankton, small fish and krill by filter feeding. It poses no danger whatsoever to divers.
Correct answer: 8
The octopus has 8 arms covered in suckers, each controlled by its own semi-autonomous nervous network. Octopuses are considered the most intelligent invertebrates: they can open jars, memorise mazes and change their appearance to camouflage themselves in seconds.
Correct answer: Humpback whale
The humpback whale (Megaptera novaeangliae) is famous for its complex, long songs lasting up to 30 minutes. These songs, produced only by males, can travel hundreds of kilometres underwater. Their structure evolves from one season to the next, as if whales are collectively learning new "melodies."
Correct answer: Plankton and small crustaceans
Manta rays are filter feeders: they consume plankton, krill and small crustaceans by swimming with their mouth open. Their wingspan can exceed 7 metres and they can weigh up to 1.5 tonnes. Despite their imposing size, they are completely harmless to humans.
Correct answer: 3
The octopus has 3 hearts: one systemic heart that pumps blood around the body, and two branchial hearts that send blood to the gills for oxygenation. Octopus blood is blue, because it contains haemocyanin (copper-based) rather than haemoglobin (iron-based).
Correct answer: Grouper
The grouper is a protogynous sequential hermaphrodite: it is born female and can become male when the dominant male of the group disappears. This mechanism, also found in other coral reef species like wrasses, ensures reproduction even when one sex is scarce.
Correct answer: Fish
The seahorse (genus Hippocampus) is a true fish, despite its unusual appearance. It has gills, a swim bladder, and swims using a small dorsal fin. Its unique trait in the animal kingdom: it is the male that carries the eggs in a ventral pouch and gives birth to the young.
Correct answer: Giant squid
The giant squid (Architeuthis dux) has eyes about 27 cm across, matched in the animal kingdom only by the colossal squid. These massive eyes allow it to detect the bioluminescence of its predators (such as the sperm whale) in the dark depths where it lives.
Correct answer: Coral bleaching
Coral bleaching occurs when water temperature rises 1 to 2°C above normal for several weeks. Corals expel the zooxanthellae (symbiotic algae) that give them their colour and provide up to 90% of their energy. Without these algae, they turn white and gradually die.
Correct answer: Manatee
The dugong and the manatee both belong to the order Sirenia. Despite living in water, their closest terrestrial relative is the elephant. Unlike manatees (found in fresh or salt water), dugongs live exclusively in the sea and feed on seagrasses.
Correct answer: 150 to 400 metres
The coelacanth (Latimeria chalumnae) lives at depths of 150 to 400 metres in the waters of the Indian Ocean. This group, which appeared 400 million years ago, was known only from fossils, the latest 66 million years old, until its rediscovery in 1938 off the coast of South Africa. It is one of the most famous examples of a "living fossil."
Correct answer: Common sea star
Sea stars (asteroids) can regenerate a lost arm within weeks to months. Some species go even further: a severed arm containing part of the central disc can regenerate an entire animal. This regenerative process is being studied by scientists for its potential medical applications.
Correct answer: Jellyfish
The jellyfish (cnidarian) has no brain, no heart, no blood and no skeleton. Its body is 95% water. Yet these animals have existed for more than 500 million years, long before the dinosaurs. Their simple nervous network allows them to detect light, gravity and chemical stimuli.
Correct answer: Sperm whale
The sperm whale (Physeter macrocephalus) is the world's largest toothed animal and a master of echolocation. It emits clicks through the spermaceti organ in its head to detect giant squid in the abyssal depths where it dives, sometimes to over 2,000 metres. Its dives can last more than 90 minutes.
Correct answer: Sea lions have external ear flaps and can "walk" on their flippers
The main morphological distinction is that sea lions have visible external ear flaps and rear flippers that rotate forward, allowing them to support their body and move on land. Seals, by contrast, have no visible external ears and must drag themselves on their belly when on land.
Stuck on one, or just curious how nasty it gets? Every hard mode question is here with its answer and the reasoning behind it.
Correct answer: Mantis shrimp
The mantis shrimp, with one of the fastest strikes in the animal kingdom.
Correct answer: Anglerfish
The anglerfish, whose light comes from bacteria living in the lure.
Correct answer: Ocean sunfish
The ocean sunfish, which can weigh more than two tonnes.
Correct answer: Sirenia
Sirenia, named after the sirens that sailors reportedly mistook them for.
Correct answer: Ampullae of Lorenzini
The ampullae of Lorenzini, which detect the faint fields of living prey.
Correct answer: Turritopsis dohrnii
Turritopsis dohrnii, which can turn back into a polyp when stressed.
Correct answer: A siphonophore
A siphonophore, a colony of specialised organisms working as one.
Correct answer: Mariana Trench
The Mariana Trench, where the Challenger Deep goes down nearly 11,000 metres.
Correct answer: Beluga
The beluga, whose chirps and whistles carry through the hulls of ships.
Correct answer: Leatherback
The leatherback, whose shell is more like thick rubbery skin than hard plate.