Surface ultrastructure and evolution of tarsal attachment structures in Plecoptera (Arthropoda: Hexapoda)

The plantar surfaces of the stonefly tarsomeres and pretarsus are examined chiefly using scanning electron microscopy (SEM) of 39 Plecoptera exemplar species representing each family within the two suborders Arctoperlaria and Antarctoperlaria. Features examined include the shape and size of the tarsomeres as well as external features of the plantar surfaces of the tarsomeres, unguitractor plate, claws, arolium and orbicula. Characteristics presumed to be part of the stonefly ground pattern were determined by mapping these features on a cladogram of stonefly phylogeny (Zwick 2000, Annual Review of Entomology 45:709–746). This analysis indicates that the following characters are part of the stonefly ground pattern: (1) cylindrical shape of the tarsomeres, (2) an elongate tarsomere 1, (3) a short tarsomere 2, (4) presence of hairy euplantulae on the plantar surfaces of tarsomeres 1 and 2, (5) absence of specialised attachment surfaces on the plantar area of tarsomere 3, (6) absence of setae on the arolium pl...