The valves have two kinds of interlocking structures that serve to hold the shell together and protect its resident. These are called lateral teeth and pseudocardinal teeth , and can be seen in the following images of a Mapleleaf. The exact shape and size of these structures are important in keying out species. This process is then repeated if the mussel wishes to move some more. Mussels can use this method to either move sideways or vertically.
Some mussels can be fairly active.
Other species may spend their whole lives in one spot. The trails resemble what you would see if you took a stick and drew a squiggle with it. If you follow the trail, you will find the animal at one end or the other, usually in a small depression. Most species of mussels have a parasitic stage of life that requires a suitable host fish. The eggs develop within the female mussel in a specially modified gill pouch called the marsupium .