Acanthocephalans, or spiny-headed worms, are endoparasites found in almost all marine, freshwater and terrestrial systems. They infect a huge range of definitive and intermediate hosts, during their life cycles, including both vertebrates and arthropods. This volume examines the distribution and abundance of the Acanthocephala, and uses this ecological information to reveal the group's enormous survival success. It discusses how the acanthocephalans have evolved differently to all other groups of parasites, and represent a distinct and alternative pathway of parasite evolution and host parasite-interactions. Written for graduate students and researchers in parasitology, ecology and zoology or anyone interested in reading about parasite ecology and evolution.