Due to the males of O. priapus still resembling other Osedax species, they use their seminal vesicle on the head to store free sperm for mating with the females. The free sperm doesn't swim well through the sea water, meaning that O. priapus need to directly transfer the sperm. To combat this, the male worm uses their stretchable trunks to enter the female worm and release the sperm into the tube.
