How do mussels attach themselves onto rocks? 🤔 Byssal threads are strong, stretchy, and silky fibres that mussels and other bivalves use to attach themselves onto surfaces, such as rocks in the intertidal zone! 🌊 As waves crash against the shore, these threads allow flexibility yet stay strongly attached to the rocks. Mussels can grow up to about 100 of these threads from a gland in their foot! California mussels are Marine bivalves with thick shells growing up to about 5in long. They are ofte