Hypothetical model of inner ear stimulation by the bipartite swim bladder extension in E. maculatus . I, lower inner ear: the gas-filled part of the swim bladder extension (green) may stimulate the lagena (light blue) via a thin bony lamella (transparent red) (A, black arrow) and the transmitted pressure signal may be further transduced via bone through the saccule (light blue) attachment (yellow) to the saccule (A and B, white arrows). II, upper inner ear: the pad (dark green and silver) may transduce vibration to the recessus (light blue) and may thus indirectly stimulate the utricle (C-D). It is noteworthy that the pad also comes very close to the posterior and horizontal semicircular canals (light blue) (E). Bone is shown in transparent red, cartilage in transparent dark blue. hsc, horizontal semicircular canal; lag, lagena; psc, posterior semicircular canal; prec, recessus situated posterior to the utricle; sac, saccule; sb ext, swim bladder extension; utr, utricle. Scale bars, 500 μm.