OBJECTIVES: Corallium rubrum, the precious red coral, is an octocoral endemic to the western Mediterranean Sea. Like most octocorals, it produces tiny, calcified structures called sclerites. Uniquely, it also produces a completely calcified axial skeleton that is a bright red color. This combination of color and hardness has made the red coral prized for centuries, leading to extensive fishing and trade for use in jewelry. Understanding how it produces this red skeleton is thus a …