So much has to be crammed into today's biology courses that basic information on animal groups and their evolutionary origins is often left out. This is particularly true of invertebrates, where most of the texts available are too large for the typical short introductory course. This volume fills the gap. An Introduction to the Invertebrates is a short guide to the invertebrate phyla, looking at their diverse forms, functions and evolutionary relationships. This book first introduces evolution and molecular methods of tracing it, then considers the distinctive body plan of each invertebrate phylum showing what has evolved, how the animals live, and how they develop. Boxes introduce physiological mechanisms and development. The final chapter combines fossil and molecular evidence to present an up-to-date view of evolutionary history, giving a more certain definition of the relationships between invertebrates. This user-friendly and well-illustrated introduction will be invaluable for all those studying invertebrates.