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 indigotin, and if left in the sun for a few minutes before becoming fast, its color turns to a blue indigo (like blue jeans).

Synonyms for this species include: Murex trunculus, L. 1758; Phyllanotus trunculus, Truncullariopsis trunculus L., 1758.

For more information please also see the related articles: Haustellum brandaris and Tyrian purple.

Distribution

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

Habitat

This murex occurs in shallow, sublittoral waters.

Shell description

H. trunculus has a broadly conical shell about 4 to 10 cm long. It has a rather high spire with seven angulated whorls. The shell is variable in sculpture and coloring with dark banding, in four varieties. The ribs sometimes develop thickenings or spines and give the shell a rough appearance.

Ancient uses of the dye

The ancient method for mass-producing the purple-blue dye from H. trunculus has not yet been successfully reproduced (because the purplish hue degrades too quickly resulting in blue only), but the use of this species has been confirmed in the archeology of Phoenicia, where large quantities of this sea snail's shells have been recovered from inside ancient live storage chambers used for harvesting. Allegedly, 60,000 murex were needed to produce one pound of dye. The dye was highly prized in ancient times. Sometimes known as royal blue, it was prohibitively expensive and only afforded by the highest ranking aristocracy.

A similar dye, Tyrian purple, which is purple-red in color, was made from a related species of marine snail, Murex brandaris. This dye (alternatively known as imperial purple, see purple) was also prohibitively expensive.

Use of the dye in Judaism

Some wool dipped in tekhelet solution, from the Murex trunculus, turning blue in the sunlight outside P'til Tekhelet in Israel.

Similarly, the Hebrew Bible also mentions a specific purple dye, called argaman ( ), which refers to the purple color this same dye produces when kept in the shade.

That is, research by Otto Elsner (Shenker College of Fibers, Ramat Gan, Israel) and Ehud Spaneir (Haifa University, Haifa, Israel) showed that by performing what is commonly referred to as "vat dyeing" based on the dyestuff from the trunculus, they could achieve colors varying from blue to purple depending on exposure to the sun when the dye solution was in its leuco (reduced) state. This phenomenon was attributed to the dyestuff being composed of indigo, mono-bromo-indigo and di-bromo-indigo. DiBromo-Indigo presents itself as purple whereas Indigo is blue. It was demonstrated that when the reduced solution of trunclus dye is esposed to sunlight, the UV-rays from the sun act to break the bromine bonds such that when oxidation occurs following the removal of the dyed fabric from the solution, pure indigo bonds to the wool, while the bromine atoms are left in the vat.

This feature of final color varying according to exposure to the sun was indeed known by the ancients, as noted in the writings of Vitruvius (1 c. BCE), ?Purple exceeds all colors in costliness and superiority of its delightful effect. It is obtained from a marine shellfish.?It has not the same shade in all the places where it is found, but is naturally qualified by the course of the sun?^[2]

References

Books

• Radwin, G. E. and A. D'Attilio, 1986. Murex shells of the world. An illustrated guide to the Muricidae. Stanford Univ. Press, Stanford, x + pp. 1-284 incl 192 figs. + 32 pls.

de:Purpurschnecke es:Murex brandaris sv:Purpursnäcka