Although other mollusks are capable of producing pearls, the emblematic bivalve making true, valuable, old-fashioned pearls is the Silver-lip Pearl Oyster, Pinctada maxima (Jameson, 1901), which may reach about 12 inches in size. That species is not native to the Atlantic Ocean, and its closest relative in our area is the much smaller Atlantic Pearl Oyster, Pinctada imbricata (Röding, 1798), at about 3 inches. The pictures show the shell and a live individual of the Atlantic Pearl Oyster. The shell (two views) is from Sanibel, and the live Oyster photographed off Palm Beach in 2014 by Anne DuPont. Anne (and us) got really lucky, because the shell has two of its gills, or ctenidia, expanded to near the shell edge. The radial “lines” running down the gills are the gill folds. Pearl Oysters are great filter feeders: one large Pearl Oyster is capable of filtering a few hundred gallons of water per day.
Photo of the live Oyster by Anne DuPont.