Phrontis tiarula, common name the western mud nassa, is a species of small sea snail with gills and an operculum, a marine gastropod mollusc in the family Nassariidae, the nassa mud snails or dog whelks.

[1] The length of the shell varies between 9 mm and 20 mm.

This species occurs in the Pacific Ocean from California to Mexico.

These snails are exclusively scavengers.

This Nassariidae-related article is a stub.