Nematodes are one of the most abundant groups of invertebrates on the face of the earth. Their numbers are estimated to range from 1,000 per cm2 in the sand-covered hydrogen sulfide "black zone" beneath the ocean floors to 3 billion in a single acre of soil. Estimates for their species diversity range from 100,000 to 10 million. The past history of nematodes is a mystery since very few fossils have been discovered. This book establishes a solid base in paleonematology with descriptions of 65 new fossil species and accounts of all previous fossil and subfossil nematodes from sedimentary deposits, coprolites, amber and mummies. It shows how nematode fossils can be used to establish lineages at various locations and time periods in the earth's history and when nematodes entered into symbiotic and parasitic associations with plants and animals.