Fig. 3

Morphology of H. illucens larval PM observed by SEM under different magnification. a was observed under ×1000 magnification, the outermost layer of the PM was arranged in continuous segments, and the length of each segment was approximately the same, about 25 μm; b and c was observed under ×2000 and ×5000 magnification respectively, the chitinous fibers at the anterior end of the outer PM layer are arranged loosely, and appears brighter, while chitinous fibers at the posterior end are densely arranged and is darker; d and e was observed under × 10, 000 and × 20, 000 magnification respectively, chitinous fibers cross each other into diamond-shaped grids, and are filled with various proteins; f The chitinous-protein fibers can be clearly observed under × 50, 000 magnification