Head anatomy of adult Coniopteryx pygmaea Enderlein, 1906: Effects of miniaturization and the systematic position of Coniopterygidae (Insecta: Neuroptera)

External and internal head structures of adult Coniopteryx pygmaea Enderlein, 1906, one of the smallest known lacewings, are described in detail for the first time. Possible effects of miniaturization and two hypotheses on the phylogenetic position of Coniopterygidae are evaluated and compared with data from literature. Several convergent modifications in C. pygmaea and other miniaturized insect species are outlined, e.g., a relative increase in the size of the brain, simplification of the tracheal system with respect to the number of tracheae, and reduction of the number of ommatidia and diameter of the facets. Further, the ocular ridge is bell-shaped and countersunk into the head capsule. The cuticle is weakly sclerotized and equipped with wax glands which are unique in Neuroptera. The total number of muscles is not affected by miniaturization. The phylogenetic analysis yields Coniopterygidae as sistergroup to the dilarid clade based on one larval character, the shape of the stylets. The enforced basal position of Coniopterygidae is supported by one disputable synapomorphy of the remaining Neuroptera, the presence of paraglossae in adults.