The classification adopted here follows Jondelius et al. (2002) and Wallberg et al. (2007), according to whom the phylogeny is (Acoela, (Nemertodermatida, Nephrozoa))
Jondelius, U.; Ruiz-Trillo, I.; Baguñà, J.; Riutort, M. 2002: The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes. Zoologica scripta, 31: 201-215.
Wallberg, A.; Curini-Galletti, M.; Ahmadzadeh, A.; Jondelius, U. 2007: Dismissal of Acoelomorpha: Acoela and Nemertodermatida are separate early bilaterian clades. Zoologica scripta, 36: 509-523.