Fig. 1. Sonic mechanism of Carapus boraborensis. (A) Left lateral view of the first five vertebrae (I-V) with the associated epineural ribs and swimbladder plate. Numbers on the swimbladder plate indicate its thickness, which decreases laterally and toward its posterior margin. (B) Schematic left lateral view of the skeleton (epineural ribs and swimbladder plate removed), sonic muscles and swimbladder. (C) Inset in B illustrates the helical organisation of the myofibrils in a single sonic muscle fiber with straight central myofibrils. SF, swimbladder fenestra; SM, sonic muscle; SP, swimbladder plate, SW, swimbladder.