Book excerpt: What makes a shell like a house? A house is a home for you, a nest is a home for a bird, and a cave is a home for a bear. But for some animals a shell is a home. Snails and turtles and crabs and clams all have shells that act as their homes and protect them from harm. In this book you'll learn all about these and other crustaceous creatures, for whom a shell is just the right sort of home.