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 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.

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Distribution

This species occurs in the Mediterranean Sea and the bordering parts of the western Atlantic Ocean.

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

  The Hebrew Bible mentions a specific blue dye, called tekhelet (Hebrew: תְּכֵלֶת‎ /təxelɛθ/) for use in tzitzit, the formal tassels or fringes of clothing, which some believe refers to the indigo dye from the Hexaplex trunculus when kept in the sun.

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

Finally, the Hebrew Bible mentions a red dye, called shani שָׁנִי [ʃɔni], which refers to the reddish Tyrian purple dye produced in the same manner from the Murex brandaris.

Those modern Ashkenazi Jews who still wear the traditional tzitzit consider the attribution of the word "tekhelet" to this particular dye as uncertain, and so some omit the blue threads altogether, to avoid mistakenly using a non-prescribed dye. Modern Ashkenazi tzitzit tassels are all-white. Sephardim, Beta Israel, Karaites, and Samaritans wear various types of blue thread in their tzitzit.