Non-monophyly of the monogeneans?

There is currently no congruence between phylogenies based on morphology, in which the Monogenea are considered a monophylum, and molecular phylogenies based on 18S or 28S rDNA, in which the Monogenea are never considered monophyletic. However, all analyses based on morphology and sperm characters or molecular data found constantly the two subgroups composing the Monogenea, namely the Monopisthocotylea and Polyopisthocotylea (or Polyonchoinea and Oligonchoinea) to be independently monophyletic. This conflict concerns not only monophyly of the Monogenea, but also the relationships of the Monopisthocotylea and Polyopisthocotylea with the Trematoda (Digenea and Aspidogastrea) and Cestoda, and therefore the phylogeny of the parasitic Platyhelminthes as a whole. It is concluded that a reappraisal of morphological synapomorphies should be undertaken.