Covering both surveys of the types of known invertebrates and their various functional systems, this book is primarily aimed at undergraduate students studying a general university course on invertebrate zoology. It will, however, also be of use as a general reference and in any other course in which invertebrates feature. The book concentrates on the essential organizational features of the various groups and different systems, and sets the material against an evolutionary background, thus presenting form and function in the light of the selective pressures and advantages which are associated with different body plans, life histories and behaviour.