Many multicellular animals do t require oxygen to live but respire anaerobically. Some of these have adapted to hostile environments, such as sulphide rich habitats, others live as parasites within host organisms, while others still can perhaps be said to look back on the early days of life on earth before anaerobic respiration had evolved. This comprehensive volume lays out detailed summaries of the strategies for anero- or axy-biosis employed by each major group of metazoan animals. It begins with a description of the physical chemistry of oxygen, followed by a dissertation on the perils - and opportunities - created for life by oxygen derived free radicals. It moves on to examine the geochrology of the accumulation of oxygen in the environment and to analyze the first explosive adaptive radiation of the Metazoa in the Ediacarian and early Cambrian. It then explores the biochemistry of sulphide dependent organisms and follows with a detailed account of the evolution of fumarate reductase, the enzyme system that makes anaerobiosis possible in many invertebrate phyla. After the survey of invertebrate phyla, there is a chapter concerned with the strategies adopted by various vertebrates for axybiotic survival, and one on the dependence of many vertebrates on anaerobic processes. The contributors are authorities from around the world. The approach to the subject is an evolutionary one, drawing from many fields in biology. This book should be of interest to parasitologists, comparative biochemists, evolutionary biologists, palaeontologists and geochemists.