足糸

Also known as byssus silk, pinna silk, sea silk, mussel silk

thumb|A mussel (genus Mytilus (bivalve)|Mytilus), attached to a rock by its byssus thumb|Illustration of the byssus of Dreissena polymorpha, the freshwater zebra mussel A byssus () is a bundle of filaments secreted by many species of bivalve mollusc that function to attach the mollusc to a solid surface. Species from several families of clams have a byssus, including pen shells (Pinnidae), true mussels (Mytilidae), and Dreissenidae.