Non-parasitic, terrestrial and aquatic nematodes

Abstract

The phylum Nematoda represents, in terms of species diversity and abundance, one of the largest groups in the animal kingdom. Although nematodes are present in terrestrial and aquatic (fresh and marine water) environments, their importance is masked by their small size. Nonparasitic nematodes are like their plant-parasitic counterparts, microscopic, vermiform creatures ranging from as small as 250 μm to approximately 10 mm in length. Irrespective of length, they seldom reach even 40 μm in diameter and are usually invisible to the naked eye. Nematodes are regarded as nonparasitic and/or beneficial when they feed on fungi, bacteria and other microorganisms as well as predate other microscopic animals. Terrestrial nematodes, both nonparasitic and plant-parasitic, are frequently found in mud or in bottom sediment after being washed into streams and other water bodies. Nematodes that occur in extreme habitats, such as cave systems, are particularly difficult to classify (aquatic or terrestrial) as very little is known about their ecological function. Nonparasitic nematodes have a range of feeding types and interact with many other soil fauna. They are grazers on bacteria and primary producers, regulators of decomposition, predators, prey for other microscopic animals as well as symbionts of bacteria and other organisms. Furthermore, nonparasitic nematodes serve as potential indicators of pollution and general environmental disturbances. The results of ecological studies in cave systems, as well as studies on nematodes as biological indicators of soil health, are emphasised in this chapter. A checklist of the nonparasitic nematodes currently recorded from South Africa is also included in this chapter