Osphradium
The osphradium is an olfactory organ in certain molluscs, linked with the respiration organ. The main function of this organ is thought to be to test incoming water for silt and possible food particles.
It is a popular idea among malacologists that the presence of an osphradium should be a molluscan synapomorphy. However, an osphradium is absent in monoplacophorans and scaphopods.
