John (Bioscience, Egham, Surrey, UK) Bridge & James (Department of Plant Pathology 
Plant Nematodes of Agricultural Importance [PDF ebook] 
A Colour Handbook

The microscopic soil and plant nematodes that are parasitic on crop plants can be very damaging, and are generally not visible to the naked eye. Their microscopic size means that associating them with crop damage is mainly dependent on determining the symptoms of their effects on plants or plant growth. The damage and symptoms caused can be visible