Spinelet variation among Hisonotus species. Figure a-f showing the extension of the bone forming a lock mechanism. In figure g–h, the bones lack the lock mechanism: aH. acuen, LBP 16276, 21.4 mm SL bH. acuen, LBP 16274, 21.1 mm SL cH. oliveirai LBP 13332, 23.7 mm SL dH. chromodontus, LBP 7964, 28.3 mm SL eH. piracanjuba, LBP 17256, 27.1 mm SL fH. paresis, NUP 10928, 23.6 mm SL gH. cf. notatus, LBP 3472, 25.8 mm SL hH. depressicauda, LBP 17474, 28.1 mm SL. Scale bar = 0.5 mm.