External macro- and micromorphology of the male of the stick insect Hermarchus leytensis (Insecta: Phasmatodea) with phylogenetic considerations.

External morphological features of adult males are described in the stick insect Hermarchus leytensis from the Philippines, a species belonging to the little-known euphasmatodean lineage Stephanacridini. Mouthparts are characterized by some likely specialized features: (1) a dentate dorsal cutting edge on the mandibles; (2) distinct differences in size and shape between the galeae; (3) absence of an apical field of trichomes on the galeae; and (4) lacinial setae not protruding from the mesal margin, which features three bearing-like protuberances. The latter character state represents a very unusual condition, not known in other phasmatodeans or even in polyneopteran insects. A distinctive characteristic of attachment devices is that each euplantula is divided into two separated pads with a smooth microstructure, as it also occurs in some members of the clade Schizodecema. Male terminalia exhibit character states previously unknown in Stephanacridini, including (1) a symmetrical type of vomer and (2) claspers equipped with ∼ 70 very minute ventral teeth on each thorn pad. Potential implications for the systematic placement of H. leytensis are discussed. The results also underline the importance of microanatomical investigations as source of substantial characters for future analyses on phasmatodean systematics.