This book differs from most parasitology texts in concentrating in detail on one group- the symbiotic platyhelminths. As the majority of these symbiotes are parasitic, the author presents a detailed explanation of the nature of such associations. The book adopts an organismal systematic approach setting the biology of parasitic platyhelminthes in an evolutionary context. Factual material is supplemented by excellent illustrations and references. This text will be of wide appeal to parasitologists, evolutionary biologists and zoologists interested in animal associations.