[[1]] is the most primitive mollusc.

Neopilina is the most primitive mollusc. 

Neopilina was discovered in the 1950s which led to the addition of a new class in phylum Mollusca. Neopilina is a highly evolved genus of modern Monoplacophora. Unlike other molluscs, Neopilina shows body segmentation, which is a primitive character. Therefore, it is a connecting link between Annelida and Mollusca.