One of the great enigmas of evolutionary biology has been how to treat animals of problematic systematic position. Many are known only as fossils, so this area has been of particular interest to palaeobiologists. This book represents a wide synthesis. It embraces not only general problems of animal classification of animals and new information on their molecular sequences that bear on their wider relationships, but also addresses more specific problems. These include details appraisals of both living and fossil groups. From the fossil record special emphasis is laid on examples from...