50 Fun Facts About Mollusks

How many hearts does an octopus have, two of which serve only to push blood through the gills?

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.

Where in its body does an octopus keep about two-thirds of its neurons, rather than in its brain?

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.

Which metal, in place of the iron in human blood, carries oxygen in octopus and squid blood?

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.

Which small cephalopod of Pacific tide pools carries enough venom to kill more than 20 adult humans?

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.

Which cephalopod of deep Antarctic waters, bearing swiveling hooks, is the heaviest invertebrate alive?

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.

Which bivalve swims by clapping its shells together and keeps watch with up to 200 tiny eyes?

Scallop eyes focus light with a curved mirror of guanine crystals instead of a lens, the same trick a reflecting telescope uses.

Ming, an ocean quahog clam later aged at 507 years, was dredged up in 2006 off which country?

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.

Paul the Octopus won fame in 2010 by correctly picking the winners of matches at which tournament?

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.

Sightings of giant squid are believed to lie behind which sea monster of Norwegian sailors' lore?

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.

Which toothed ribbon, often compared to a tongue, do snails and most other mollusks scrape food with?

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.

Which body layer of a mollusk secretes the shell and forms the cavity that houses the gills?

Mantle tissue does a second job in squid and octopuses: its muscular walls squeeze water out of the cavity to jet the animal along.

The word mollusk traces back to the Latin mollis, an adjective with which meaning?

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.

Mollusks are the second-largest animal phylum by species, behind which group that includes insects and crabs?

Arthropods lead overall, but in the sea mollusks come first: they are the largest marine phylum, with about 23% of all named marine organisms.

Which class of mollusks, the largest by far, twists its body 180 degrees in a process called torsion?

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.

Scaphopods, burrowers in seabed sand, are better known by which name, after their curved, tapering shape?

Tusk shells of the genus Dentalium were strung on thread and used as money by the peoples of the Pacific Northwest.

Which flattened mollusks cling to shoreline rocks beneath a shell made of eight overlapping plates?

Chitons can curl into a ball when knocked off a rock, and their scraping teeth are coated with magnetite, a hard iron oxide mineral.

Which rock-clinging sea snail has teeth with a tensile strength even greater than that of spider silk?

Limpet teeth are reinforced with nanofibers of the iron mineral goethite, so thin that the flaws which weaken most materials barely matter.

Which iridescent material of stacked aragonite platelets lines abalone shells and makes up most pearls?

Nacre, better known as mother-of-pearl, shimmers because its platelets are about as thick as a wavelength of visible light.

Which branch of zoology is devoted to the study of mollusks, from garden snails to giant squid?

Malacology has its own specialists: teuthologists study only squid, octopuses and their relatives, while other researchers concentrate on empty shells.

Which shelled cephalopod, often called a living fossil, lacks suckers but can have over 90 tentacles?

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.

Which cephalopod's chalky internal shell is sold as a mineral supplement for caged pet birds?

Cuttlefish were called sepia in Greek and Latin, which is why the reddish-brown color still carries that name.

Which extinct spiral-shelled squid relatives, named for a ram-horned Egyptian god, died out with the dinosaurs?

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.

Which reef bivalve gets most of its food from algae living in its own tissues?

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.

Which wood-boring bivalve is nicknamed the termite of the sea?

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.

Which Pacific Northwest clam, the largest burrowing species on Earth, has a neck up to a meter long?

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.

Which tropical reef hunter spears fish with a venomous, harpoon-like tooth and can kill a person?

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.

Which shell-less mollusk of Pacific redwood forests is the official mascot of UC Santa Cruz?

Banana slug won the job in a student vote, and Reader's Digest named it the best college mascot in 2004.

Which deep-diving mammal counts giant squid among its prey and often carries scars thought to come from them?

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.

Which seafood menu name, borrowed from Italian, goes back to a Latin word for a pen case or ink pot?

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.

Which sea snail's large shell, blown as a horn, does Ralph use to gather the boys in Lord of the Flies?

Conch shells are still blown as horns from the Caribbean to India, where one is sounded every evening in many Bengali Hindu homes.

Which small, glossy sea snail supplied the shells used as money across Africa and Asia for centuries?

Cowrie shells made their mark on language: Ghana's currency, the cedi, is named after them, and the Chinese character for money began as a drawing of one.

Which part of a giant Pacific octopus, made of tough chitin, limits how small a gap it can squeeze through?

Its beak sets the limit, so a large adult can compress the rest of its body through a space as small as 50 mm across.

Which compound, also the main ingredient of chalk and limestone, makes up most of a mollusk's shell?

Calcium carbonate crystals in a shell take one of two forms, calcite or aragonite, laid down on an organic framework that controls where and how fast they grow.

Cephalopod ink gets its dark color mainly from which pigment, the same one that tints human skin and hair?

Melanin is mixed with mucus in the ink, and computer simulations suggest it may also overwhelm the scent receptors of hunting sharks.

Which fingernail-sized bivalve from the Black and Caspian seas invaded the Great Lakes in the 1980s?

Zebra mussel larvae are thought to have arrived in the ballast water of ocean-going ships, and managing them in the Great Lakes has been put at over $500 million a year.

Which Japanese entrepreneur, credited with the first cultured pearl, opened a Ginza jewelry store in 1899?

Kokichi Mikimoto impressed Thomas Edison, who told him in 1927 that culturing pearls was supposed to be biologically impossible.

Tyrian purple, the costly dye of ancient Phoenicia later reserved for emperors, came from which animals?

Murex snails had to be gathered by the tens of thousands to make the dye, which is why purple cloth became a mark of rank.

Cephalopods are the only mollusks with which type of circulatory system, the kind that vertebrates also have?

Closed circulation keeps blood inside vessels at all times, while snails and clams let theirs flow out of a short artery into the main body cavity.

Which pigment-filled skin organs, stretched by tiny muscles, let octopuses change color in an instant?

Chromatophores in cephalopods are worked directly by muscles and nerves, whereas chameleons produce a similar effect through cell signaling instead.

Which muscular tube, also called the funnel, do squid and octopuses blast water through to jet along?

Siphon jets usually drive the animal backward, but the tube can be pointed in different directions to steer, and ink is carried out on the same stream.

The vampire squid, despite its name, feeds mainly on what, gathered with two long retractile filaments?

Detritus, from the remains of dead jellies to the droppings of animals living higher up, is its diet; the name came from its dark color and cloak-like webbing, not from its habits.

The Hawaiian bobtail squid hides its silhouette using light made by what, living in a special organ?

Bacteria of the species Aliivibrio fischeri are fed sugar and amino acids by the squid, and each hatchling has to pick them out of seawater full of other microbes.

Which cell parts does the eastern emerald elysia, a sea slug, steal from algae and keep working for months?

Chloroplasts turn the slug bright green and let it photosynthesize like a plant; some individuals have kept going for up to a year after only a few feedings.

Freshwater snails host the parasitic flatworms that cause which tropical disease, also known as bilharzia?

Schistosomiasis is caught through contact with fresh water carrying parasites released by infected snails, and one man in Germany got it from a snail in his aquarium.

Which tough threads, known to cooks as the beard, do mussels spin to anchor themselves to rocks?

Byssus threads can stretch by more than a third before they yield, and a mussel typically moors itself with between 20 and 60 of them.

Which modified limb does a male octopus or squid use to transfer his sex cells to the female during mating?

Hectocotylus combines the Greek for hundred and cup; Georges Cuvier coined it in 1829 after finding one lodged in a female and taking it for a parasitic worm.

Which free-swimming larval stage do most sea snails and clams pass through, often after a trochophore stage?

Veliger larvae drift and feed in the plankton for weeks to months, which lets slow-moving adults seed regions far from where they live.

Which structure in the squid, wide enough for electrodes, let Hodgkin and Huxley show how nerves fire?

Giant axon fibers can be 1.5 mm across, built to speed up the squid's escape jet, and the experiments on them earned a Nobel Prize.

Which trapdoor-like plate do many sea snails carry on the foot to seal the shell opening after they withdraw?

Operculum is Latin for cover, and people noticed the plate early: the oldest known depiction of one is on a seal made by the Minoan civilization.

Which vividly colored sea slugs can store the stinging cells of their prey in outgrowths on their backs?

Nudibranchs lost their shells in the course of evolution and rely on borrowed weapons instead: the stolen stingers pass through the gut without harming them.