According to Hejnol (new EST-based survey, PNAS: in review), they found that Xenoturbella are grouping with Acoela and Nemertodermatida. All these three groups may be sister to all other Bilateria ("Nephrozoa"), or to Deuterostomia.
Chaetognatha position is more or less stable, they are sister to all Spiralia (Ecdysozoa + Lophotrochozoa), or to Lophotrochozoa.
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A. Shipunov