This group, also known as the Phasmidea in some classification systems, contains most of the species of parasitic nematodes.
This group contains many species that are free-living, as well as numerous parasites on plants and animals. Life cycles may be direct, or indirect with one or two intermediate hosts. Adult and larval stages parasitize vertebrates and invertebrates.
This group is characterized by the presence of phasmids, which can be difficult to see on most preparations, and other obscure features. The terminal portion of the excretory system is lined with cuticle.