The fan mussel, also known as the noble pen shell (
Pinna nobilis) is a
bivalve shellfish indigenous to the
Mediterranean Sea. It is an ordinary
animal, with no remarkable traits, with the exception of its
unique byssus gland.
The byssus gland produces an extremely fine
filament that the fan mussel uses to fasten itself to the sea floor. Because this filament's source is exclusively the byssus gland, it is an especially rare material, and its fineness, lightness and deep golden coloration make it a luxury material in the production of
textiles. People have been harvesting this material -- simply referred to as byssus -- for the last 3000 years, and
civilizations such as
ancient Rome,
Chaldea,
Persia and
China produced and traded in it.
Most byssus trade, at least that taking place in
western Europe, died down in the
late Middle Ages. There are few remnant examples of byssus cloth from this period, but the few that do exist are mostly women's gloves, woven so fine that they could be packed into an evacuated
walnut shell. Byssus trade resumed in
Sicily in the last century, but its trade is irregular, and it has no common market price.
The word "byssus" comes from the word used in the
Vulgate books
Genesis and
Exodus to describe fine
Egyptian linen. It is understood that the fabric referenced in the
Vulgate was not in fact the fabric of the fan mussel; the material now called "byssus" is actually named for the cotton product.