Overview of the shell of O. edulis. Top: Outer view of the shell indicating the line of strongest growth (LSG) from the umbo to the margin, which runs perpendicular to the growth lines. Middle: Cross section following the LSG with the direction of growth (DOG) from left to right. Magnified is the measurement area under reflected (bottom left) and fluorescent light (bottom right) with 1–Coating, 2–Growth line, 3–Disturbance line, 4–in situ fluorescent marking, 5–measurement. Under florescent light, the shell does show natural fluorescence visible in yellow on the edge between shell and the coating.