Mollusks
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50 free Mollusks trivia questions with answers — trivia quiz, new questions added Oct 2026.
Mollusks are one of the most varied groups in the animal kingdom. The same phylum holds a garden snail, an oyster cemented to a reef and a squid that hunts in the deep sea, and all of them are built on one shared body plan. This quiz covers the phylum the way a biology course does, then goes further. It starts with the anatomy every student meets: the layer that builds the shell, the feeding organ found in almost every class, how blood and nerves are arranged, and what separates the major classes from one another. From there it moves to the animals themselves, with venomous species, record holders for size and age, fossils, larvae and parasites, and on to the ways people have used mollusks for food, money, dye and jewelry. It suits students revising for a zoology or marine biology test, teachers who need a ready set of questions on invertebrates, and anyone who has watched an octopus open a jar and wanted to know more. Every answer comes with a short explanation.
30 of 50 questions with answers and explanations. Play the quiz
Q 01How many hearts does an octopus have, two of which serve only to push blood through the gills?
Three
Three hearts share the work, and the main one stops beating whenever the octopus swims, which is why it loses energy quickly and mostly crawls.
Q 02Where in its body does an octopus keep about two-thirds of its neurons, rather than in its brain?
In its arms
In its arms, which can move and sense largely on their own without waiting for orders from the brain; even a severed one still responds to touch.
Q 03Which metal, in place of the iron in human blood, carries oxygen in octopus and squid blood?
Copper
Copper sits at the core of hemocyanin, a protein dissolved straight into the plasma that moves oxygen better than hemoglobin does in cold, oxygen-poor water.
Q 04Which small cephalopod of Pacific tide pools carries enough venom to kill more than 20 adult humans?
Blue-ringed octopus
Blue-ringed octopus venom contains tetrodotoxin, the nerve poison also found in pufferfish, and no antivenom exists; victims pull through only if someone keeps them breathing.
Q 05Which cephalopod of deep Antarctic waters, bearing swiveling hooks, is the heaviest invertebrate alive?
Colossal squid
Colossal squid can weigh about 495 kg and have the largest eyes documented in the animal kingdom, each roughly the width of a dinner plate at 27 to 30 cm.
Q 06Which bivalve swims by clapping its shells together and keeps watch with up to 200 tiny eyes?
Scallop
Scallop eyes focus light with a curved mirror of guanine crystals instead of a lens, the same trick a reflecting telescope uses.
Q 07Ming, an ocean quahog clam later aged at 507 years, was dredged up in 2006 off which country?
Iceland
Iceland's cold northern shelf yielded the oldest individual animal ever precisely aged; born around 1499, Ming died when researchers froze it, unaware of how old it was.
Q 08Paul the Octopus won fame in 2010 by correctly picking the winners of matches at which tournament?
FIFA World Cup
FIFA World Cup matches made Paul a star: from a tank in Oberhausen, Germany, he chose between two flag-marked boxes of food and got all eight of his 2010 picks right.
Q 09Sightings of giant squid are believed to lie behind which sea monster of Norwegian sailors' lore?
Kraken
Kraken lore reached a wide audience through bishop Erik Pontoppidan, who wrote in the 1750s that the beast was sometimes mistaken for a group of small islands.
Q 10Which toothed ribbon, often compared to a tongue, do snails and most other mollusks scrape food with?
Radula
Radula teeth wear down at the front and are replaced from behind like a conveyor belt; bivalves are the only mollusk class without one, because they filter their food instead.
Q 11Which body layer of a mollusk secretes the shell and forms the cavity that houses the gills?
Mantle
Mantle tissue does a second job in squid and octopuses: its muscular walls squeeze water out of the cavity to jet the animal along.
Q 12The word mollusk traces back to the Latin mollis, an adjective with which meaning?
Soft
Soft was the sense Linnaeus had in mind when he chose the Latin name in 1758, at first for a mixed bag of invertebrates that did not even include the species with shells.
Q 13Mollusks are the second-largest animal phylum by species, behind which group that includes insects and crabs?
Arthropods
Arthropods lead overall, but in the sea mollusks come first: they are the largest marine phylum, with about 23% of all named marine organisms.
Q 21Which cephalopod's chalky internal shell is sold as a mineral supplement for caged pet birds?
Cuttlefish
Cuttlefish were called sepia in Greek and Latin, which is why the reddish-brown color still carries that name.
Q 22Which extinct spiral-shelled squid relatives, named for a ram-horned Egyptian god, died out with the dinosaurs?
Ammonites
Ammonites got the name from Pliny the Elder, who called the fossils horns of Ammon, and they changed so fast that geologists use them to date rock layers.
Q 23Which reef bivalve gets most of its food from algae living in its own tissues?
Giant clam
Giant clam legends tell of trapped divers and even an attack on a canoe, yet the adults are fixed in place and cannot shut their shells completely.
Q 14Which class of mollusks, the largest by far, twists its body 180 degrees in a process called torsion?
Gastropods
Gastropods end up with the anus more or less above the head, and with 65,000 to 80,000 living snails and slugs they are outnumbered as a class only by the insects.
Q 15Scaphopods, burrowers in seabed sand, are better known by which name, after their curved, tapering shape?
Tusk shells
Tusk shells of the genus Dentalium were strung on thread and used as money by the peoples of the Pacific Northwest.
Q 16Which flattened mollusks cling to shoreline rocks beneath a shell made of eight overlapping plates?
Chitons
Chitons can curl into a ball when knocked off a rock, and their scraping teeth are coated with magnetite, a hard iron oxide mineral.
Q 17Which rock-clinging sea snail has teeth with a tensile strength even greater than that of spider silk?
Limpet
Limpet teeth are reinforced with nanofibers of the iron mineral goethite, so thin that the flaws which weaken most materials barely matter.
Q 18Which iridescent material of stacked aragonite platelets lines abalone shells and makes up most pearls?
Nacre
Nacre, better known as mother-of-pearl, shimmers because its platelets are about as thick as a wavelength of visible light.
Q 19Which branch of zoology is devoted to the study of mollusks, from garden snails to giant squid?
Malacology
Malacology has its own specialists: teuthologists study only squid, octopuses and their relatives, while other researchers concentrate on empty shells.
Q 20Which shelled cephalopod, often called a living fossil, lacks suckers but can have over 90 tentacles?
Nautilus
Nautilus shells are divided into chambers holding gas and liquid that the animal adjusts to control its buoyancy, a design little changed in hundreds of millions of years.
Q 24Which wood-boring bivalve is nicknamed the termite of the sea?
Shipworm
Shipworm burrowing gave engineer Marc Brunel the idea for the tunneling shield, the iron frame that let workers dig the first tunnel under the Thames.
Q 25Which Pacific Northwest clam, the largest burrowing species on Earth, has a neck up to a meter long?
Geoduck
Geoduck clams are among the longest-lived animals, able to pass 160 years, and their ages can be read from yearly growth bands in the shell.
Q 26Which tropical reef hunter spears fish with a venomous, harpoon-like tooth and can kill a person?
Cone snail
Cone snail venom has killed about 30 people on record, yet one of its components is now sold as ziconotide, a last-resort drug for severe chronic pain.
Q 27Which shell-less mollusk of Pacific redwood forests is the official mascot of UC Santa Cruz?
Banana slug
Banana slug won the job in a student vote, and Reader's Digest named it the best college mascot in 2004.
Q 28Which deep-diving mammal counts giant squid among its prey and often carries scars thought to come from them?
Sperm whale
Sperm whale diets are mostly medium-sized squid, and no person has ever watched one fight a giant squid; the white scars are the only evidence of the battles.
Q 29Which seafood menu name, borrowed from Italian, goes back to a Latin word for a pen case or ink pot?
Calamari
Calamari is the Italian plural for squid; the Latin root calamus meant a reed pen, a name tied to the ink the animal squirts and, some say, its pen-shaped internal shell.
Q 30Which sea snail's large shell, blown as a horn, does Ralph use to gather the boys in Lord of the Flies?
Conch
Conch shells are still blown as horns from the Caribbean to India, where one is sounded every evening in many Bengali Hindu homes.