First μ-CT-based 3D reconstruction of a dipteran larva-the head morphology of Protanyderus (Tanyderidae) and its phylogenetic implications.

The larval head of Protanyderus was examined and documented using innovative techniques, with emphasis on internal structures. A chart listing all head muscles of dipteran larvae and other holometabolan groups is presented in the Supporting Information. The results are compared to conditions found in other nematoceran lineages. The larval head of Protanyderus is characterized mainly by plesiomorphic character states such as the complete and largely exposed head capsule, the long coronal suture, V-shaped frontal sutures, lateral antennal insertion areas, a transverse labrum, a nearly horizontal plane of mandibular movements, mandibles lacking a movable distal part, a mesal hook and mesal or distal combs, separated maxillary endite lobes, a comparatively complete array of muscles, and a brain only partly located within the head capsule. An anteriorly toothed hypostomal plate and dense labral brushes of microtrichiae are also likely groundplan features of Diptera. The pharyngeal filter is a possible apomorphy of Diptera excl. Deuterophlebiidae (or Deuterophlebiidae + Nymphomyiidae). The messors have also likely evolved early in the dipteran crown group but are absent in the groundplan. The phylogenetic interpretation of externolateral plates with growth lines is ambiguous. Autapomorphies of Tanyderidae are differences between the third and fourth instar larvae, the roof-like extension above the antennal insertion area, the dorsal endocarina, and the posterodorsal internal ridge. The phylogenetic position of Tanyderidae is controversial, but features of the larval head do not support a proposed sistergroup relationship between Tanyderidae and Psychodidae. Both groups differ in many features of the larval head, and we did not identify a single potential synapomorphy. Larval characters alone are insufficient for a reliable phylogenetic reconstruction, though they vary greatly and apparently contain phylogenetic information. The evaluation of these features in the context of robust molecular phylogenies will be a sound basis for the reconstruction of complex evolutionary scenarios for the megadiverse Diptera.