Abstract
This paper discusses various aspects of nematode composition and distribution, including the ubiquitous dispersal of nematodes, the variability of species compositions between areas, lakes within an area and within lakes, the (supplemental) use of molecular methods for nematode identification, species richness and composition in lakes and in rivers, and the relationship between species richness and trophic status. Biotic and abiotic factors controlling species composition, and factors creating variability within a lake (horizontal species distribution and vertical species distribution within the sediment) are highlighted.