Structural optimization and amorphous calcium phosphate mineralization in sensory setae of a terrestrial crustacean (Isopoda: Oniscidea).

•Sensory setae on Porcellio legs are thin and stiff, necessitating great fracture resistance.•The stiff shaft of each seta is linked to the exoskeleton by a flexible joint membrane.•The shaft is mineralized with amorphous calcium phosphate.•Interchanging layers of axially aligned and helicoidally arranged chitin fibers form the shaft.•The orientation of fibers and amorphous calcium phosphate may increase fracture resistance.