Parasitic Nematodes are microscopic, whitish to transparent, unsegmented worms. They occupy almost every conceivable habitat on earth, both aquatic and terrestrial, and are among the most common multicelled organisms. Nematodes are generally wormlike and cylindrical in shape, often tapering at the head and tail ends; they are sometimes called roundworms or eelworms. There are thousands of kinds of nematodes, only a small number are plant feeding parasites.