Varix (mollusc)

: varices) is an anatomical feature of the shell of certain sea snails, marine gastropod molluscs.

Gastropods whose shells have varices are primarily families and species within the taxonomic groups Littorinimorpha and Neogastropoda.

The varix is a thickened axial ridge, a subcylindrical protrusion, in the shell which exists in some families of marine gastropods.

A varix is located at intervals around the whorl, and is formed by considerable thickening of the outer lip during a resting stage in the growth of the shell.

Some other genera, for example Murex, are armed with protective spines which may be straight or curved, and which are formed by the varices closing or curling around their axis.