Nematoda) are at risk of extinction by virtue of being dependent on threatened or endangered species of vertebrate host. They also conclude that parasite species diversity does not map linearly onto host species diversity, and that approximately three-quarters of all links in food webs involve a parasitic species. These findings provide a sobering reminder that the current extinction pulse is affecting many kinds of organisms (not just the conspicuous megafauna), and that extinction processes could therefore have many unforeseen ramifications for ecosystem operations.