Acercaria display an unusually broad array of adhesive devices occurring on different parts of the legs. Attachment structures of all major subgroups are described and illustrated. Nineteen characters of the distal leg region were combined with a data matrix containing 99 additional morphological characters of different body parts. The results of the cladistic analysis are largely congruent with current hypotheses. Zoraptera are not retrieved as close relatives of Acercaria. The monophyly of the entire lineage and of the major subgroups Psocodea, Phthiraptera, and Hemiptera is confirmed. Our data also support the monophyly of Auchenorrhycha and a sister-group relationship between Thysanoptera and Hemiptera (Condylognatha). In contrast to other lineages of insects, the hairy type of adhesive device is present only in one group within the Acercaria (Heteroptera, Cimicomorpha). The arolium is present in the groundplan but missing in several groups (e.g. Psocodea, Cicadoidea, Aphidoidea). Pretarsal pulvilli evolved several times independently. Tarsal euplantulae and different specialized clasping devices have evolved within Phthiraptera, whereas pretarsal attachment devices are missing in this ectoparasitic group. The potential to modify pretarsal attachment devices in their structural details has probably contributed to the very successful diversification of the predominantly phytophagous Hemiptera.

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The male postabdomen and the internal parts of the male genital system of Bibio marci (Bibionomorpha) were examined and reconstructed 3‐dimensionally. Several features differ from the presumptive dipteran groundplan. The bases of the gonopods are fused with each other and with tergite IX. The penis is not tube‐shaped and only sclerotized on the ventral side. The vasa deferentia are S‐shaped, and two pairs of accessory glands are present. In contrast to these characteristics, the arrangement of the internal parts is probably close to the ancestral condition. With its specific shape, the penis is well suited for the transfer of a spermatophore. The dorsal sclerite of the copulatory organ probably represents the medially fused parameres. A cladistic analysis of 27 characters of the postabdomen yielded two most parsimonious trees, with the strict consensus as follows: Nannochoristidae (outgroup) + (Culicidae [Culicomorpha] + ((Nymphomyiidae + (Tipulidae + Trichoceridae)) + (Tabanidae [Brachycera] + (Bibionidae, Anisopodidae, Axymyiidae [Bibionomorpha])))). Potential synapomorphies of Bibionomorpha (including Axymyiidae) and Brachycera are the fusion of sternum IX with the gonocoxites, the fusion of the parameres forming the dorsal sclerite and the presence of an entire series of postabdominal muscles (M4, M20, M23, M26, M27, M31, M35 and M37). The results of the analysis are preliminary as it is based on a single‐character system with a limited taxon sampling. However, the main result – a clade Bibionomorpha + Brachycera – is fully compatible with current hypotheses on dipteran phylogeny.

The systematic positions of Enicocephalomorpha and Dipsocoromorpha are still controversial and the available morphological information is very fragmentary. Consequently, head structures of Cryptostemma (Dipsocoromorpha: Dipsocoridae) and Systelloderes (Enicocephalomorpha: Enicocephalidae) were investigated in detail using SEM, serial sectioning and computer-based 3D-reconstruction. The observed features were compared to putatively homologous structures in Nepomorpha, Leptopodomorpha, Cimicomorpha, and Pentatomomorpha. A cladistic analysis based on 71 cephalic characters scored for 16 heteropteran terminals and outgroup taxa resulted in a strict consensus of two minimum length trees. The monophyly of Heteroptera is strongly supported. However, in the present study, the branching pattern within the group is not compatible with recent hypotheses (e.g., Nepomorpha paraphyletic herein). Characters of the head alone are not sufficient to reconstruct the basal branching events in Heteroptera. This is arguably due to homoplasy related to similar feeding habits. Consequently, we evaluated the cephalic characters based on previously published cladograms. A hypothesis with Enicocephalomorpha as the sister group of the remaining Heteroptera (Euheteroptera), followed by Dipsocoromorpha, required the lowest number of steps. Euheteroptera are supported by the presence of distinct bucculae, and Neoheteroptera (Euheteroptera excl. Dipsocoromorpha) by the presence of paired postoccipital condyles and distinctly bi-lobed principal salivary glands. A conspicuous autapomorphy of Enicocephalomorpha is the distinct constriction of the head capsule posterad of the compound eyes and probably also the elongation of the head and the presence of “scapus sclerites”. Dipsocoromorpha differ strongly form Enicocephalomorpha in their head morphology. Convincing cephalic autapomorphies are lacking. Gerromorpha are characterized by cephalic trichobothria originating in a deep pit and by a quadrangular mandibular lever.