Byssus Threads on a Blue Mussel

Blue mussels use byssus threads (which you can see on the right, in front of the barnacle shell) to attach to rocks and sometimes to stop a predator from making them a meal.
(Flickr user Tantivy_Jade)
Blue mussels use byssus threads (which you can see on the right, in front of the barnacle shell) to attach to rocks and sometimes to stop a predator from making them a meal.