Acoelomorpha, Catenulida e Rhabditophora (Rieger et al., 1991), since Rhabditophora also includes the parasitic forms.
They are distributed into the following taxa: Acoela, Nemertodermatida, Catenulida, Macrostomida, Polycladida, Prolecithophora, Lecithoepitheliata, Revertospermata, Proseriata, Tricladida, Dalytyphloplanida and Kalyptorhynchia (Schockaert et al., 2008; Van Steenkiste et al., 2013).
The following key-words were used: Platyhelminthes, Acoela, Nemertodermatida, Catenulida, Prolecithophora, Rhabdocoela, Temnocephalida, Macrostomida, Lecithoepitheliata or Revertospermata and Brazil.
Dalytyphloplanida and Catenulida are the most species-rich, with about 28% and 18% of the recorded species, respectively, followed by Acoela (15%), Prolecithophora (11%), Proseriata (10%), Kalyptorhynchia (9%), and Macrostomida (7%).
Although adult morphology varies vastly across the group, many core Lophotrochozoa (including the Mollusca, Annelida [including Vestimentifera, Pogonophora, and Echiura, and possibly Myzostoma, and Sipunculida], Gnathostomulida, Nemertea, dicyemid Mesozoa, Entoprocta, and some Platyhelminthes [including polyclad Turbellaria, Catenulida
, and Macrostomida]) exhibit spiral cleavage, a highly conserved pattern of early development.
Molecular analyses that include other lower turbellarian groups (for example, the Catenulida
and the Nemertodermatida) and the Orthonectida, a group tentatively included in the Mesozoa, will provide further information for understanding the phylogenetic position of the dicyemids.