Ontogeny of the hyopalatine arch, jaws, and opercular series of Apteronotus leptorhynchus (MTD-F 40169, cleared and double stained). A 8.6 mm NL. B 12.1 mm SL. C 20.4 mm. D 66.0 mm SL. Abbreviations: An, angulo-articular; Cm, coronomeckelian; De, dentary; Enpt, endopterygoid; Hy, hyomandibular; Hy-SyC, hyo-symplectic cartilage; Iop, interopercle; LLCO, lateral line canal ossification; MC, Meckel’s cartilage; Met, metapterygoid; Mx, maxilla; MX-AC, articular cartilage of maxilla; Op, opercle; PAp, pars autopalatina; PMet, pars metapterygoidea; Pmx, premaxilla; Pop, preopercle; PQ, pars quadrata; Q, quadrate; Ra, retroarticular; Sop, subopercle; Sy, symplectic.