1. Megasolena estrix Linton 1910 has been incorrectly classified in the Allocreadiidae.
2. The possession of two pairs of longitudinal lymph vessels, a remarkable hermaphroditic sac as well as other minor characters indicate relationship to the Paramphistomidae.
3. Hapladena Linton 1910 possesses these same characters and is considered related to Megasolena.
4. These characters are considered to be of more fundamental taxonomic value than the position of the acetabulum.
5. A new subfamily, Megasoleninae, of the family Opistholebetidae is named and described.