Ultrastructure of attachment specializations of hexapods (Arthropoda): evolutionary patterns inferred from a revised ordinal phylogeny Author R. G. Beutel Author S. N. Gorb text J. Zool. Syst. Evol. Research 2001 39 177 207 journal article 10.1046/j.1439-0469.2001.00155.x 95b3d62f-8fcc-4088-873f-b33f4a63d3fc 2360323 8 Plecoptera The two proximal tarsomeres of the three­segmented tarsus bear euplantulae in the larger species ( Zwick 1980 ). An arolium is present between the strong, paired claws ( Fig. 3a ). The arolium cuticle bears chitinous threads oriented at an angle to the surface ( Fig. 4I ).