Pictorial Handbook on Plant and Soil Nematodes of Rajasthan

From the preface: Nematodes are found in almost all habitats, but are often overlooked because most of them are microscopic in size. For instance, a square yard of wood land or agricultural habitat may contain several million nematodes. Many species are highly specialized parasites of vertebrates, including humans, or of insects and other invertebrates. Other kinds are plant parasites, some of which can cause economic damage to cultivated plants. Nematodes are particularly abundant in marine, freshwater and soil habitats.

Soil is an excellent habitat for nematodes. Because of their importance to agriculture, much more is known about plant-parasitic nematodes than other kinds of nematodes which are present in soil. Most kinds of soil nematodes do not parasitize plants, but are beneficial in decomposition of organic matter. These nematodes are referred as free-living nematodes.