The image above shows a preserved, dissected freshwater mussel. Note the conspicuous fold of tissue called the mantle (1). In molluscs the mantle is a sheath of skin that hangs down in two folds around the soft body and encloses a mantle cavity, which performs many of the same functions as a coelom in other animals. The outer side of the mantle secretes the shell while the inner side is ciliated, and along with gills (2), participates in gas exchange.

Note the prominent anterior adductor muscle (3) and posterior adductor muscle (4) that draw the two valves together to enclose and protect the animal from predators. The lateral hinge teeth (5) that help the valves to securely interlock can also be seen in this image. Observe the heart (6), which  is contained within the pericardial cavity (7) located in a dorsal position just below the lateral hinge teeth (5).  In molluscs, this cavity represents the remains of a much-reduced coelom. Note the conspicuous, hatchet-shaped foot (8) that is used for burrowing. In the image shown, a portion of the foot has been removed to reveal the greenish digestive gland (9) and gonad (10).