The shells of bivalves in this family are fragile and have a long and triangular shape, and in life the pointed end is anchored in sediment using a
byssus. The shells have a thin but highly iridescent inner layer of
nacre in the part of the shell near the
umbos (the pointed end). The family Pinnidae includes the fan shell,
Atrina fragilis, and
Pinna nobilis, the source of
sea silk. Some species are also fished for their food value. ==Human use==