Growth Lines

Note: In temperate latitudes such as the metro region growth lines are laid down annually. Complete growth lines may thus be counted to approximate mussel age.

Anodonta implicataalewife floater

Anodonta implicata
alewife floater

Ligumia nasutaeastern pondmussel

Ligumia nasuta
eastern pondmussel

Growth lines vary among species, appearing as concentric circles of ridges or contrasting bands of color that mark the stages of growth.
Lampsilis cariosayellow lampmussel

Lampsilis cariosa
yellow lampmussel

Pyganodon cataractaeastern floater

Pyganodon cataracta
eastern floater

The color and texture of the periostracum may conceal or highlight the pattern and color of the growth lines.