Key to Families of SEURATOIDEA

1 Buccal cavity absent or, if present, derived from cheilostom; cuticle constituting walls of cheilostom having same structure and staining reactions as external body cuticle........................................................ Quimperiidae

- Buccal cavity formed from modifications of anterior end of oesophagus (oesophastom); walls of oesophastom surrounded by oesophageal tissue........................................................................... Cucullanidae