Byssus

Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilidae), and Dreissenidae.

Many species of mussels secrete byssus threads to anchor themselves to surfaces, with families including the Mytilidae, Arcidae, Anomiidae, Pinnidae, Pectinidae, Dreissenidae, and Unionidae.

[1][2] The byssus, or byssal complex, is composed of multiple extracellular collagenous threads that are placed radially by the mussel from a central stem.

Mechanical testing of live mussels has shown that byssal threads can extend 39% before yield and 64% before breaking, at a nominal strain rate of 10 mm/min.

[7] When a mussel's foot encounters a crevice, it creates a vacuum chamber by forcing out the air and arching up, similar to a plumber's plunger unclogging a drain.

By curling its foot into a tube and pumping the foam, the mussel produces sticky threads about the size of a human hair.

[16] Byssus often refers to the long, fine, silky threads secreted by the large Mediterranean pen shell, Pinna nobilis.

[18][19] The byssus of Atrina pectinata, a shell of the same family, has been used in Sardinia as a substitute for critically endangered Pinna nobilis, to weave sea silk.