Structure and formation of the byssus complex in Mytilus (Mollusca

A review is presented of the mechanism of byssus production in the genus Mytilus. The pedal glands which secrete the byssus material are described, followed by an account of the morphology, structure and chemistry of the byssus itself. Finally, the release or shedding of the byssus from the pedal tissues is discussed. Many adult bivalve molluscs attach to the substratum by means of a complex of proteinaceous threads produced by pedal glands. This complex, known as the byssus, is believed to have originated as a larval structure (Yonge, 1962), the neotenous retention of which led to the development of heteromyarian and monomyarian shell forms and enabled bivalves to adopt an epifaunal life. The byssal apparatus is common in post-larval stages where it acts primarily as a means of temporary attachment and it is present in many species which lack a byssate adult, e.g. Mya arenaria L. and Venerupis pullastra (Montagu) (Yonge, 1962). Adults of a wide range of life habits have retained a byssus, it being present in active swimmers, e.g. some pectinids (Stanley, 1970), rock borers such as Botula (Mytilacea) and Tridacna (Cardiacea) (Yonge, 1955, 1962), th