D: Gonangulum sclerotisation (LCa9 and LCp9) and adjacent parts of surrounding sclerotisations shown schematically, explaining design of Fig. 4AeF (compare Figs. 2A,C and 4E); gonangulum dark grey, other sclerotisations midgrey; patches in light grey are muscle attachments, ribbons in very dark grey are sulci. Orientation in all figures: [ anterior. Scale bar 0.5 mm, valid for Fig. 2A,B.