Terrestrial nematodes can be distinguished in bacterial feeding nematodes, fungal feeders, plant parasites, carnivorous nematodes and omnivores. Because of their economic importance, plant parasites got a lot of attention. Plant parasites can be found in different taxa which are hardly related. Most plant parasites belong to the Tylenchida. These nematodes, for example Rotylenchus robustus, are characterized by a stylet which can be protruded to puncture a plant cell. Plant parasites can also be distinguished based on the location where they feed. Ectoparasites remain outside the plant root whereas endoparasites live in the roots. Rotylenchus behaves intermediate: only the anterior part of the body penetrates the root. Other characteristics of the Tylenchida are the annulated cuticle and the presence of a lateral field with, at the level of the anal opening, a structure which is termed phasmid, its function is still unknown.