What is byssal thread?
byssal thread meaning one of many thin, hairlike filaments secreted by certain mollusks for attachment to a substrate
The byssal gland is located within the foot of the mussel. It produces secretions which are used to form byssal threads for attachment to substrates. (Photo: Great Lakes Sea Grant Network Exotic Species Library, Ontario Ministry of Natural Resources)
reference: Coral Reef Information System – GlossaryWhat is