Nematodes are incontestably the most numerous and the most diverse metazoans in freshwater habitats, and these properties bestow exceptional significance to their role in the environment. An array of functional roles has been attributed to them: they are grazers on bacteria and primary producers, regulators of decomposition of plant material, predators, prey for other animals, and closely associated symbionts of bacteria and other organisms. Freshwater nematodes are central in the context ...