This group of organisms, also called eelworms, is found in almost every part of the terrestrial environment, and range in size from the large animal parasites, e.g. Ascaris (about 20 cm long) in livestock, to the tiny soil-inhabiting species (about 0.5 mm long). Non-parasitic species may be beneficial, feeding on plant remains and soil bacteria, and helping in the formation of humus (see p321). The general structure of the nematode body is shown in Figure 14.28. A feature of the plant parasitic species is the spear in the mouth region, which is thrust into plant cells. Salivary enzymes are then injected into the plant and the plant juices sucked into the nematode (see Figure 14.27). Nematodes are very active animals, moving in a wriggling fashion in soil moisture films, most actively when the soil is at field capacity, and more slowly as the soil either waterlogs or dries out. Five horticulturally important types are described below.
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