How do male phallostethoid fishes use the priapium during mating?

In phallostethoid fishes, the male utilizes the priapium—a fleshy, asymmetrical intromittent organ located under the throat—to facilitate mating. This specialized structure is formed from the fish's modified pelvic fins. During the reproductive process, the male uses the priapium to achieve internal fertilization of the female. Despite this advanced anatomical adaptation for internal fertilization, viviparity (the production of live young) is not known to occur in these fishes.1