Hexaplex Trunculus

Hexaplex trunculus (also known as Murex trunculus or the banded dye-murex) is a medium-sized species of sea snail, a marine gastropod mollusk in the family Muricidae, the murex shells or rock snails.

This species of sea snail is important historically because its hypobranchial gland secretes a mucus that the ancient Canaanites/Phoenicians used as a distinctive purple-blue indigo dye. One of the dye's main chemical ingredients is dibromo-indigotin, and if left in the sun for a few minutes before becoming fast, its color turns to a blue indigo (like blue jeans).