Small, but oh my! Head morphology of adult Aleuropteryx spp. and effects of miniaturization (Insecta: Neuroptera: Coniopterygidae).

We present the first morphological study of the internal head structures of adults of the coniopterygid genus Aleuropteryx, which belong to the smallest known lacewings. The head is ventrally closed with a gula, which is unique in adult Neuroptera and otherwise developed in Megaloptera, the sister group of Neuroptera. The dorsal tentorial arms are directed posteriorly and fused, forming an arch that fulfills functions otherwise taken by the tentorial bridge. A newly found maxillary gland is present in both sexes. Several structural modifications correlated with miniaturization are recognized: a relative increase in the size of the brain, a reduction in the number of ommatidia and diameter of the facets, a countersunken cone-shaped ocular ridge, and a simplification of the tracheal system. The structure of the head differs strikingly from that of the previously studied species Coniopteryx pygmaea, indicating a greater variability in the family Coniopterygidae, which might be another effect of miniaturization.