Unraveling the insect head: Segmentation and pancrustacean homologies

Abstract

The segmental composition of the arthropodan head is a long-standing biological question. This is particularly controversial in insects where considerable fusion and modification obfuscate the postembryonic segmentation. Here we propose a reinterpretation of the insect head morphology and segmentation, which also accords with current genetic and embryological data. The new interpretation of a generalized insect head is based on the discovery of intercalary segment remnants (the intercalates), thanks to the use of 3D-reconstruction of a Cretaceous thripidan and to a reassessment of the 'anterior tentorial arm' as the anteriormost part of a lateral segmental suture from the contact of the head lobe and gnathal segments during development. We show that the two-jointed mandibular articulation is likely symplesiomorphic for Insecta, no longer supporting the clade 'Dicondylia', the most diverse lineage of all insects. We discuss new perspectives on the 'labrum' in Pancrustacea.

Keywords: Arthropoda; Dicondylar mandible; Intercalary segment; Lora; Origin of tentorium.