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Shell Day: A Story of 24 Hours and 24 Molluscan Lives
An hourly guide that follows twenty-four mollusks to reveal the fascinating lives behind their shells.
From morning to night and from the Arctic to the equator, snails, clams, and other shell-making mollusks have busy days. In this short book, acclaimed author and marine biologist Helen Scales shows readers exactly how these animals spend their time. Each chapter of Shell Day features a single mollusk during a single hour, highlighting twenty-four different species.
Far in the north, the Svalbard archipelago lies deep in the darkness of the polar night. And yet, in what remains a scientific mystery, Iceland scallops continue their daily rhythms, closing and opening their fan-shaped shells using an internal clock. At noon, we observe a clam shell sitting still on the seabed of a sandy tropical lagoon. The two shells open slightly, and a pair of rounded eyes peep out. A small, rust-colored coconut octopus hiding inside lets the clam shells fall apart and gathers them up in her arms. This mollusk’s ancestors long ago lost the ability to produce their own shells, but the cephalopod is happy to use another animal’s castoff as a temporary home. At ten that night, we find ourselves in Southern France. A male moon snail uses his huge, fleshy foot like a plow as he digs down into the seabed in search of food. When the moon snail finds a cockle, he swiftly smothers it, then sets about drilling, aided by a daub of acidic slime. Cockles are tasty, but so are other moon snails, and his snacking has a cannibalistic flavor.
For each chapter, illustrator and cartoonist Aaron John Gregory has depicted molluscan scenes with entrancing pen-and-ink drawings. Working together to narrate and illustrate these unique moments in time, Scales and Gregory have created an engaging read that is a perfect way to spend an hour or two—and a true gift for beachcombers, naturalists, or anyone eager to learn about the mollusks that make their favorite shells.
From morning to night and from the Arctic to the equator, snails, clams, and other shell-making mollusks have busy days. In this short book, acclaimed author and marine biologist Helen Scales shows readers exactly how these animals spend their time. Each chapter of Shell Day features a single mollusk during a single hour, highlighting twenty-four different species.
Far in the north, the Svalbard archipelago lies deep in the darkness of the polar night. And yet, in what remains a scientific mystery, Iceland scallops continue their daily rhythms, closing and opening their fan-shaped shells using an internal clock. At noon, we observe a clam shell sitting still on the seabed of a sandy tropical lagoon. The two shells open slightly, and a pair of rounded eyes peep out. A small, rust-colored coconut octopus hiding inside lets the clam shells fall apart and gathers them up in her arms. This mollusk’s ancestors long ago lost the ability to produce their own shells, but the cephalopod is happy to use another animal’s castoff as a temporary home. At ten that night, we find ourselves in Southern France. A male moon snail uses his huge, fleshy foot like a plow as he digs down into the seabed in search of food. When the moon snail finds a cockle, he swiftly smothers it, then sets about drilling, aided by a daub of acidic slime. Cockles are tasty, but so are other moon snails, and his snacking has a cannibalistic flavor.
For each chapter, illustrator and cartoonist Aaron John Gregory has depicted molluscan scenes with entrancing pen-and-ink drawings. Working together to narrate and illustrate these unique moments in time, Scales and Gregory have created an engaging read that is a perfect way to spend an hour or two—and a true gift for beachcombers, naturalists, or anyone eager to learn about the mollusks that make their favorite shells.
- GenresAnimalsNatureNonfiction
208 pages, Hardcover
Published July 3, 2026
About the author
Helen Scales
26 books259 followersIn their review of my first book, Poseidon’s Steed, the Economist called me “The aptly named Helen Scales” and I guess they’re right. I do have a bit of a thing about fish (get it?).
Across the airways and in print, I’m noted for my distinctive and occasionally offbeat voice that combines a scuba diver’s devotion to exploring the oceans, a scientist’s geeky attention to detail, a conservationist’s angst about the state of the planet, and a storyteller’s obsession with words and ideas.
I have a Cambridge PhD and a monofin, I’ve drunk champagne with David Attenborough and talked seahorse sex on the Diane Rehm show. I spent four years (on and off) chasing after big fish in Borneo and another year cataloguing marine life surrounding 100 Andaman Sea islands.
These days I write books and articles, I make podcasts and radio, travel the world in search of stories, and do my best to spend as much time as I can in the sea as a scuba diver, free diver and rookie surfer. I’m a fellow of the Royal Geographical Society and a member of the steering committee for the Museum of Curiosity. I’m also a proud aunt, I sew dresses, grow organic vegetables, put on high heels and dance Argentine tango, play piano, sing in the shower, and make a mess in a printmaking studio.
Across the airways and in print, I’m noted for my distinctive and occasionally offbeat voice that combines a scuba diver’s devotion to exploring the oceans, a scientist’s geeky attention to detail, a conservationist’s angst about the state of the planet, and a storyteller’s obsession with words and ideas.
I have a Cambridge PhD and a monofin, I’ve drunk champagne with David Attenborough and talked seahorse sex on the Diane Rehm show. I spent four years (on and off) chasing after big fish in Borneo and another year cataloguing marine life surrounding 100 Andaman Sea islands.
These days I write books and articles, I make podcasts and radio, travel the world in search of stories, and do my best to spend as much time as I can in the sea as a scuba diver, free diver and rookie surfer. I’m a fellow of the Royal Geographical Society and a member of the steering committee for the Museum of Curiosity. I’m also a proud aunt, I sew dresses, grow organic vegetables, put on high heels and dance Argentine tango, play piano, sing in the shower, and make a mess in a printmaking studio.
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Displaying 1 - 4 of 4 reviews
July 20, 2026
Wonderful little book on mollusks by marine biologist Helen Scales, author of _Spirals in Time: The Secret Life and Curious Afterlife of Seashells_. The second of the Day book by University of Chicago Press that I have read, this book follows the same format, each chapter focusing on one mollusk species at a particular hour of the time of the day or night and accompanied by one illustration (in this case by Aaron John Gregroy), starting with the Garter Cone Snail of West Africa (Conus genuanus) at midnight and ending with the Giant Triton of Australia (Charonia tritonis) at 11 pm local time, each chapter catching that species in the act.
Despite the name of the book, not every mollusk has a shell and in one case there is a chapter with a shell but no mollusk in a wonderful chapter on hermit crabs.
After fun mollusk facts (mollusks are among the most species-rich phyla in the ocean; all shells have a basic logarithmic spiral shape), it is on to the mollusks hour by hour. Highlights include the Common Limpet of Europe (Patella vulgata, over time etching scars into the rocks they live on, these home scars getting deeper over time and somehow limpets always find their home scars tide after tide), Humboldt Squid of the eastern Pacific (Dosidicus gigas; able to create through use of chromatophores in the skin bold and vivid color displays for intra-squid communication), Bobtail Squid of Hawaii (Euprymna scolopes; have a complex symbiotic relationship with bioluminescent bacteria, vital for both helping the squid hunt on moonlit nights and in maintaining its daily rhythms), Wavy-Rayed Lampmussel of North America (Lampsilis fasciola; a freshwater mussel that has a lure attractive to fish, not to prey on fish, but to use them for part of its reproductive cycle), Giant Clam of Southeast Asia (Tridacna gigas; the largest living bivalves, have specialized cells called iridocytes to reflect and scatter sunlight in its body to symbiotic algae called zooxanthellae), Button Top Shell of Singapore (Umbonium vestiarium; filter feeding gastropods), the Argonaut of the Indian Ocean (Argonauta argo; a pelagic octopus that makes its own shell, shells that they can come all the way out of, with smaller argonauts frequently hitching rides on jellyfish, comb jellies, siphonophores, and trash), and the Nutmeg Snail of the eastern Pacific (Cancellaria cooperii; a vampiric snail particularly fond of torpedo rays).
Despite the name of the book, not every mollusk has a shell and in one case there is a chapter with a shell but no mollusk in a wonderful chapter on hermit crabs.
After fun mollusk facts (mollusks are among the most species-rich phyla in the ocean; all shells have a basic logarithmic spiral shape), it is on to the mollusks hour by hour. Highlights include the Common Limpet of Europe (Patella vulgata, over time etching scars into the rocks they live on, these home scars getting deeper over time and somehow limpets always find their home scars tide after tide), Humboldt Squid of the eastern Pacific (Dosidicus gigas; able to create through use of chromatophores in the skin bold and vivid color displays for intra-squid communication), Bobtail Squid of Hawaii (Euprymna scolopes; have a complex symbiotic relationship with bioluminescent bacteria, vital for both helping the squid hunt on moonlit nights and in maintaining its daily rhythms), Wavy-Rayed Lampmussel of North America (Lampsilis fasciola; a freshwater mussel that has a lure attractive to fish, not to prey on fish, but to use them for part of its reproductive cycle), Giant Clam of Southeast Asia (Tridacna gigas; the largest living bivalves, have specialized cells called iridocytes to reflect and scatter sunlight in its body to symbiotic algae called zooxanthellae), Button Top Shell of Singapore (Umbonium vestiarium; filter feeding gastropods), the Argonaut of the Indian Ocean (Argonauta argo; a pelagic octopus that makes its own shell, shells that they can come all the way out of, with smaller argonauts frequently hitching rides on jellyfish, comb jellies, siphonophores, and trash), and the Nutmeg Snail of the eastern Pacific (Cancellaria cooperii; a vampiric snail particularly fond of torpedo rays).
October 13, 2026
Very much like the other books in this series, like Flower Day, with each hour of the day represented by a mollusc. Each mollusc gets a few pages of description, usually quite interesting, and a black and white drawing. I would definitely prefer color images, but this series just doesn't do that. I most liked the octopuses, which tracks for me. They're my favorite animals.
August 13, 2026
A bite sized story into the wonders of the molluscan world. My favorite creatures were the bobtail squid, argonaut, limpet, lamp mussel, giant clam and coconut octopus!
August 22, 2026
Essentially reading, beautifully presented and fascinating information. I shall pick up shells with more respect from now on. What little scary miracles each one turns out to be!
Displaying 1 - 4 of 4 reviews