The head morphology of the potentially basal heteropteran lineages Enicocephalomorpha and Dipsocoromorpha (Insecta: Hemiptera: Heteroptera)

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