Luxury fiber is a strange thing. Linen comes from flax (which has some legitimate claims to being the first domesticated plant). Silk is derived from the cocoons of lepidoterans. Qiviut comes from the undercoats of musk-oxen. One of the rarest of all luxury fibers comes from an even more peculiar source. “Sea silk” is produced by collecting and spinning the long micro filaments or “byssus” secreted by several kinds of bivalve mollusks–expecially Pinna nobilis (a large saltwater clam once widespread in the Mediterranean ocean). Pinna nobilis can grow up to a meter (3 feet) in size and anchors itself to the ocean floor with an extremely fine fiber it excretes from a land in its foot.
The fiber was mentioned in various Greek, Egyptian, and Roman sources (and an analog seems to have existed in ancient China) but differentiating sea silk made from mollusk fibers from similar luxury fibers like cocoon silk, or fine linen seems to be more a matter of context rather than of terminology. Sea silk is finer than the true silk produced from silkworm cocoons. It was said that a pair of ladies’ gloves made of sea-silk could be folded into one half of a walnut shell because the fiber was so profoundly delicate. Sea silk was warm and durable but it was infamous for attracting clothing moths. A few pieces have survived in museums including the extraordinary mediaeval chasuble of St. Yves pictured below.
Unfortunately the Pinna nobilis clams which are the source of byssus fibers have declined rapidly in number thanks to overfishing, pollution, and the general decline of the Mediterranean sea-grass beds. Other fibers like seaweed based cellulose or watered silk have adopted the “sea silk” name further confusing the issue. Today the sea silk industry only barely survives in Sardinia where a handful of aging practitioners keep it alive–more for tradition’s sake than economic reward.