This book is an introductory guide to invertebrate evolution for university students and others. It is designed to be read as a whole to interest and orientate students who encounter invertebrates. The book is needed because in our overcrowded biology courses sadly little is taught about invertebrates; again and again in recent years students have asked me ‘Is there a little book?’ because the current comprehensive invertebrate textbooks are too big and heavy for their requirements.

This second edition is needed because in the last six years there has been a surge of information from molecular methods of tracing phylogeny. Knowledge of genes and genetic control of development has given us exciting new tools for assessing relationships between phyla, and new fossil finds have contributed also. The result is that there is an increased interest in invertebrates. Yet the relationships between animals can mean nothing without some basic knowledge of the animals themselves: an introductory guide to invertebrates is more than ever necessary. Accordingly, this book maintains the structure of the first edition, with a chapter devoted to each phylum to establish how the animals with this particular body plan can make a living and what forms have been able to evolve, with a brief paragraph at the end indicating relationships. The final chapter (20) explains and discusses our present understanding of invertebrate relationships.