An order of the class Enopola of the phylum Rhynchocoela, characterized by possession of an elaborate armed proboscis consisting of an anterior thick-walled tube, a median portion armed with stylets, and a posterior blind tube. The alimentary system possesses a cecum, and in some species (such as Amphiporus lactifloreus) the foregut (stomach) can be everted into the prey to achieve extracorporeal digestion prior to ingestion. There are two suborders, the Monostylifera and Polystylifera, separated on the number of stylets in the proboscis. Monostylifera include fresh-water, terrestrial, and symbiotic species, as well as the more common marine littoral forms.