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.