Key to the Parathyone species

1. Anterior process of the calcareous ring radial plate as long as the base of the radial plate................. P. braziliensis

- Anterior process of the calcareous ring radial plate distinctly longer than the base of radial plate...................... 2

2. Body wall buttons strongly knobbed with rounded knobs (Fig. 4 d–f); one Polian vesicle; longitudinal muscle splitting off before midlength of body cavity.............................................................. P. surinamensis

- Body wall buttons slightly knobbed with triangular knobs (Fig. 4 a–c); two Polian vesicle; longitudinal muscle splitting off after midlength of body cavity...................................................... Parathyone itapuaensis sp. nov.