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. “Do you ever ask yourself, What do mollusks do all day? Or perhaps even, What is a mollusk? You’ll find the answers here. You’re sure to learn something, as I did, while you enjoy this informative book that highlights members of the second-most diverse but often-overlooked animal phylum, which includes snails, squids, clams, and slugs. Though still animals, those creatures are about as distantly related to you and me as possible. They offer a different and fascinating take on life.” ― Janet Voight, author of "From the Seashore to the Seafloor" “Marine biologist Helen Scales introduces readers to twenty-four remarkable species of mollusks, each revealing fascinating behaviors that unfold over the course of a typical molluscan day. Beautifully illustrated and packed with engaging and informative stories, this book offers delightful insights into the lives of those extraordinary animals.” ― Andreia Salvador, senior curator of marine Mollusca at the Natural History Museum, London “With the soul of a poet and a talent for finding the most intriguing trivia about familiar seaside sights, marine biologist Scales turns the mundane into the magical.” -- Praise for Scales ― Discover “A sprawling, ambitious underwater journey studded with fascinating tidbits.” -- Praise for Scales ― New York Times Book Review “Punctures assumptions with the power of a cone snail dart.” -- Praise for Scales ― Spectator “An enchanting, accessible tour of the seashell and its place and purpose within the natural world.” -- Praise for Scales ― Kirkus Reviews “Scales . . . brings a marine biologist’s eye and aficionado’s heart to these musings on seashells. . . . [Her] eclectic approach to this ancient bridge between the human and natural worlds conveys her curiosity and appreciation.” -- Praise for Scales ― Publishers Weekly “A fascinating journey into the strange and captivating world of mollusks. Carefully researched and entertaining throughout. . . . Relentlessly interesting.” -- Praise for Scales ― Science Helen Scales is a marine biologist, author, and broadcaster who teaches at the University of Cambridge. She is a regular contributor to National Geographic Magazine and The Guardian and is a storytelling ambassador for the Save Our Seas Foundation. Her most recent books include What the Wild Sea Can Be and Ocean Art: From the Shore to the Deep . Aaron John Gregory  is a scientific illustrator and professional aquarist living on the coast in Pacifica, California with his wife and two daughters. Shell Day is his fifth collaboration with Helen Scales.