Shell Day: A Story of 24 Hours and 24 Molluscan Lives

by Helen Scales, Aaron John Gregory (Illustrator)

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.

208 pages, Hardcover

Expected publication May 17, 2026

About the author

In 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.