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 2 Collembola ( Schaller 1970 ) The pretarsus is a very short but separate leg section. On the ventral side, opposed to the single claw a spur­like empodial appendage and an empodial tubercle are present, and in some springtails an accessory empodial appendage. The claw is triangular in cross­section with a median edge – sometimes toothed – and two lateral edges. The lateral edges are equipped with one lateral tooth in most species. Sminthurids (e.g. Sphyrotheca sp.) are characterized by a membranous claw sheath (tunica; Schaller 1970 ).