The Purple dye murex is a gastropod mollusk, or a sea slug, with a robust shell adorned with thorns with an unmistakable shape.
It has a wide oval opening with a thin serrated lip; the external color varies from yellow to dark green; the meat is yellowish-white with dark ends at the two apices. There are two main species, commonly called male and female, of very dark and lighter color respectively.
The Purple dye murex of Olbia is the male one, dark, with white savory meat.