Order Haplopharyngida Karling, 1974
Pharynx simplex. Brain encapsulated, two ventro-lateral nerve cords. Ovary single, no accessory organs, female pore posterior to male; male with circle of hard straight stylets, some associated with a glandular accessory organ. Free-living, marine.
Haplopharyngidae Karling, 1965
For some time these were considered part of the Macrostomida.