This animal starts off, as a tiny free swimming animal, before it settles down to become the mussel you see here. The California mussel can grow 3 inches a year. They can move around a little bit, by releasing little threads that anchor them to a rock or dock. These threads are so strong doctors use a similar material, for medical purposes. This strong anchor allows them to get into a better position for food. Mussels filter about a gallon of water a day.