Evolutionary scenarios for unusual attachment devices of Phasmatodea and Mantophasmatodea (Insecta)

The distal parts of the legs of representatives of Phasmatodea and Mantophasmatodea were examined. The condition found in Mantophasma zephyra and Timema nevadense is described in detail. In both species the arolium is highly modified, i.e. strongly enlarged and pan-shaped and densely covered with acanthae. The presence of acanthae on the euplantulae is another very unusual feature shared by the two taxa. A cladistic analysis based mainly on a data matrix from an earlier study of the authors was carried out, with the inclusion of three new characters derived from attachment devices. The results suggest three possible evolutionary scenarios for the features in question. If Phasmatodea are the sister group of Mantophasmatodea, the apomorphic features of the attachment devices may be synapomorphies of both groups, with different degrees of reversal within the suborder Euphasmatodea. A branching pattern Phasmatodea + (Mantophasmatodea + Grylloblattodea) is consistent with the presence of an enlarged pan-shaped arolium and euplantulae with acanthae in the common ancestor of this lineage, with reversal in Grylloblattodea and within Euphasmatodea. The acanthae on the surface of the arolium may or may not have evolved independently in Timema. A placement of Phasmatodea as sister taxon of Orthoptera, Dictyoptera, or a clade comprising both groups implies that the features in question have evolved independently in phasmids and Mantophasmatodea.