Reconstruction of Exopinacites singularis and of its possible swimming advantage involved by the presence of an umbilical lid. Speculative functional advantage of the umbilical lid, which was combined with a deep umbilical sinus in the aperture, allowing water to enter directly from the swimming direction into the mantle cavity. The position of the hyponome can be deduced from the hyponomic sinus.
Monnet et al. BMC Evolutionary Biology 2011 11:115 doi:10.1186/1471-2148-11-115