Recent comparative studies of billfishes (Istiophoridae and Xiphiidae) have provided evidence of differences in the form and function of the rostra (bill) among species. Here, we report the discovery of a new structure, lacuna rostralis, on the rostra of sailfish Istiophorus platypterus , which is absent on the rostra of swordfish Xiphias gladius , striped marlin Kajikia audax and blue marlin Makaira nigricans . The lacunae ro...