The function of pocket shark pectoral pockets has puzzled scientists over decades. Here, we show that the pockets of the American Pocket Shark (Mollisquama mississippiensis) contain a brightly fluorescent stratified cubic epithelium enclosed in a pigmented sheath and in close contact with the basal cartilage of the pectoral fins; cells of this epithelium display a centripetal gradient in size and a centrifuge gradient in fluorescence. These results strongly support the idea that pocket shark's pockets are exocrine holocrine glands capable of discharging a bioluminescent fluid, potentially upon a given movement of the pectoral fin. Such capability has been reported in many other marine organisms and is typically used as a close-range defensive trick. In situ observations would be required to confirm this hypothesis.