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The female cephalothorax of Xenos vesparum (Strepsiptera, Xenidae) is described and documented in detail. The female is enclosed by exuvia of the secondary and tertiary larval stages and forms a functional unit with them. Only the cephalothorax is protruding from the host’s abdomen. The cephalothorax comprises the head and thorax, and the anterior half of the first abdominal segment. Adult females and the exuvia of the secondary larva display mandibles, vestigial antennae, a labral field, and a mouth opening. Vestiges of maxillae are also recognizable on the exuvia but almost completely reduced in the adult female. A birth opening is located between the head and prosternum of the exuvia of the secondary larva. A pair of spiracles is present in the posterolateral region of the cephalothorax. The musculature of the female cephalothorax is strongly reduced. Only muscles of the mandibles, foregut and a pair of longitudinal muscles are present. The nervous system is strongly flattened dorsoventrally. The brain is shifted to the prothoracic region together with the frontal ganglion. Well-developed optic nerves are present and vestiges of stemmata. The suboesophageal ganglion is fused with the thoracic and abdominal ganglia thus forming a compact undivided ganglionic mass. The dorsal vessel forms a ring-shaped structure around the brain. A valvula cardiaca is present between the posterior foregut and midgut. The midgut is strongly bloated and probably involved in inflating the cephalothorax during pheromone release of the female. The Nassonov’s glands are located on the ventral side of the cephalothorax. Structural features of the females of X. vesparum are compared to conditions found in the head and thorax of the free-living females of Mengenillidae and cephalothoracic characters of Stylops ovinae (Stylopidae). The highly modified morphology of female Stylopidia is dicussed with respect to their permanent endoparasitism and also with their neotenous development.

Zoraptera are a cryptic and enigmatic group of insects. The species diversity is lower than in almost all other groups of Hexapoda, but may be distinctly higher than presently known. Several new species were described from different regions recently. The systematic placement was discussed controversially since the group was discovered 100 years ago. Affinities with Isoptera and Psocoptera were discussed in earlier studies. A sister group relationship with Acercaria (Psocodea, Thysanoptera, Hemiptera) was proposed by W. Hennig, for the first time based on a strictly phylogenetic argumentation. More recent studies consistently suggest a placement among the “lower neopteran orders” (Polyneoptera). Close affinities to Dictyoptera were proposed and alternatively a sister group relationship with Embioptera or with Embioptera + Phasmatodea (Eukinolabia), respectively. The precise placement is still controversial and the intraordinal relationships are largely unclear. Recent transcriptome analyses tentatively suggest a clade Zoraptera + Dermaptera as sister group of all other polyneopteran orders. The oldest fossils are from Cretaceous amber. An extinct genus from this era may be the sister group of all the remaining zorapterans. The knowledge of the morphology, development and features related to the reproductive system greatly increased in recent years. The general body morphology is very uniform, whereas the genitalia differ strongly between species. This is likely due to different kinds of selection, i.e. sexual selection in the case of the genital organs. The mating pattern also differs profoundly within the order. A unique external sperm transfer occurs in Zorotypus impolitus. A species-level phylogeny and more investigations of the reproductive system should have high priority.