a Nearly complete gladius, dorsal view, scale bar = 2 cm. b Detail of the apical part forming conus (c), mf median field, lf lateral fields, hbz hyperbolar zones, dashed lines mark the hyperbolar zones separating lateral fields from the median field, scale bar = 2 cm. c Reconstruction of the gladius, red lines demarcate hyperbolar zones, mf enlarged median field, lhf length of hyperbolar zones, scale bar = 10 cm, rectangle shows the postion of the d, scale bar = 2 cm. d Detail of the lateral field with hyperbolar zone and median field, scale bar = 2 cm. e Detail of the median field with marked concentric growth lines (gl).