Figure 7.

The phylogenetic scenario for spiralian evolution envisaged by the ‘U-tube’ theory in an illustrative spiralian phylogeny. Some taxa are grouped, so that ‘Lophophorata’ = Phoronida + Brachiopoda; ‘Polyzoa’ = Cycliophora, Ectoprocta and Entoprocta; ‘Platyzoa’ = the various smaller taxa (including e.g. Gnathostomulida and Syndermata) treated by Laumer et al. [78]. Some of these groups, especially the Polyzoa, are controversial, but their absence may not materially affect the argument herein. The position of Nemertea is unclear, but they may be the sister group to Lophophorata [78].