The insect head rewound: Clarifications to the groundplan of Hexapoda (Pancrustacea)

The organization of the hexapod head remains a cornerstone problem in arthropod systematics, central to segmental homology, character definition, higher-level phylogeny, and functional and evolutionary morphology. Recently, Nel et al (2025) proposed an alternative interpretation of insect head segmentation that departs markedly from established anatomical and comparative frameworks. We evaluate the internal consistency and external coherence of that hypothesis using their model groups, broader taxonomic samples, prior studies (including crustaceomorph Pancrustacea) and our own investigations. We identify multiple implausible anatomical interpretations and logical contradictions in their reconstruction. Our reanalysis, supported by microtomographic imaging (μ- and SR-μ-CT), shows that the proposed revision lacks empirical foundation (e.g. Psocodea), does not meet its own definitions (e.g. Neuropteroidea), misidentifies homologs (e.g. Coleoptera, Formicidae), and is unsupported by fossil or developmental evidence. Consequently, the new theory yields unreliable homology statements and obscures groundplan conditions and character polarities of the hexapod head. ... mehrWe therefore reject the hypothesis that “intercalate” and “promandible” sclerites existed in the groundplan of Hexapoda, and the assumed plesiomorphy of dicondyly. Our findings clarify relationships among major head sclerites, endoskeletal elements, and the head capsule's strengthening ridges, underscoring the need for comprehensive anatomy, broad sampling, and logical rigor in resolving arthropod head evolution.