Which marine snail produces a purple dye historically used in royal robes?

The marine snail associated with the purple dye once used in royal robes is the murex snail. More precisely, several predatory sea snails in the family Muricidae produce the famous dye known as Tyrian purple or royal purple.

The dye came from a secretion of the snail’s hypobranchial gland. Important historical species included Bolinus brandaris, Hexaplex trunculus, and Stramonita haemastoma. The dye’s main coloring compound is 6,6'-dibromoindigo, and its production was extraordinarily labor-intensive: thousands of snails could yield only a small amount of pigment.

Tyrian purple was especially associated with Phoenician cities such as Tyre and later with Roman and Byzantine rulers. Its rich color, resistance to fading, and scarcity made purple cloth a symbol of wealth and authority. A common mix-up is to treat “murex” as one exact species; historically, the term covers several related dye-producing snails rather than a single animal.