What type of freshwater mussel from Arkansas rivers is harvested for cultured pearls?

The Washboard Mussel is the correct choice because it is known to be one of the freshwater mussels from which cultured pearls can be harvested. This species has the right biological makeup, allowing it to create pearls when irritants enter the shell. The process involves inserting a small bead or piece of tissue into the mussel, triggering it to form layers of nacre, which ultimately results in a cultured pearl.

In contrast, while other mussel species might play important ecological roles, they are not commonly associated with pearl production. The Zebra Mussel, for instance, is an invasive species that can negatively impact ecosystems and does not produce pearls. The Rainbow Mussel and the Pocketbook Mussel are also not primarily known for pearl cultivation. Thus, the Washboard Mussel holds a specific significance in the aquaculture of pearls.