Cephalic anatomy of Zorotypus weidneri New, 1978: new evidence for a placement of Zoraptera

Abstract

External and internal head structures of Zorotypus weidneri were examined, documented with SEM images and photographs, and reconstructed 3-dimensionally. The results are compared with published results on Z. hubbardi and with conditions found in other hemimetabolan lineages, with a main focus on the polyneopteran orders and on Psocoptera and Thysanoptera representing Acercaria. Externally the head of both zorapteran species is very similar but they differ in some internal features such as the presence (Z. hubbardi) or absence (Z. weidneri) of an ampullo-aortic muscle of the antennal heart and a well-developed cervical gland. Cephalic characters are analysed phylogenetically addressing the controversial issue of the placement of Zoraptera. A position within monophyletic Polyneoptera is confirmed, but weakly supported. The analysis yielded a sister group relationship between Zoraptera and Plecoptera but also with a low support value. The placement of Zoraptera with morphological data is impeded by many preserved plesiomorphies such as the orthognathous head orientation, the complete tentorium, the free labrum or the largely unmodified orthopteroid mouthparts in the winged morphs, and also by modifications apparently caused by miniaturization. Similarly, anomalies in the genome cause problems in the assessment of the phylogenetic affinities of the group.