[3] This sea snail is historically important because its hypobranchial gland secretes a mucus used to create a distinctive purple-blue indigo dye.

This species lives in the Mediterranean Sea and the Atlantic coasts of Europe and Africa, specifically Spain, Portugal, Morocco, the Canary Islands, Azores.

Today, with stronger reduction agents which are more transparent, it is possible to break the original purplish hue molecule and degrade it by introducing it to UV sun rays, resulting in a more blue color.

Therefore, archeologists have confirmed Hexaplex trunculus as the species used to create the purple-blue dye; large numbers of shells were recovered from inside ancient live-storage chambers that were used for harvesting.

A similar dye, Tyrian purple, which is purple-red in color, was made from a related species of marine snail, Murex brandaris.

Jews may have used the pigment from the shells to create a sky-blue, tekhelet, dye to put on the fringes that the Torah specifies for the corner of the prayer shawl.