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    Review of 'The evolution of head structures in lower Diptera'

    The evolution of head structures in lower DipteraCrossref
    Manuscript is rigorous and provides a useful contribution to its research area, should be published
    Average rating:
        Rated 5 of 5.
    Level of importance:
        Rated 5 of 5.
    Level of validity:
        Rated 4 of 5.
    Level of completeness:
        Rated 5 of 5.
    Level of comprehensibility:
        Rated 5 of 5.
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    The evolution of head structures in lower Diptera

    The head of adult dipterans is mainly characterized by modifications and more or less far reaching reductions of the mouthparts (e.g., mandibles, maxillae), linked with the specialization on liquid food and the reduced necessity to process substrates mechanically. In contrast, the compound eyes and the antennae, sense organs used for orientation and for finding a suitable mating partner and oviposition site, are well developed. Some evolutionary novelties are specific adaptations to feeding on less liquefied substrates, such as labellae with furrows or pseudotracheae on their surface, and the strongly developed pre- and postcerebral pumping apparatuses. In some dipteran groups specialized on blood the mandibles are still present as piercing stylets. They are completely reduced in the vast majority of families. Within the group far-reaching modifications of the antennae take place, with a strongly reduced number of segments and a specific configuration in Brachycera. The feeding habits and mouthparts of dipteran larvae are much more diverse than in the adults. The larval head is prognathous and fully exposed in the dipteran groundplan and most groups of lower Diptera. In Tipuloidea and Brachycera the head is partly or largely retracted and the sclerotized elements of the external head capsule are partly or fully reduced. The head of Cyclorrhapha is largely reduced. A complex and unique feature of this group is the cephaloskeleton. The movability of the larvae is limited due to the lack of thoracic legs. This can be partly compensated by the mouthparts, which are involved in locomotion in different groups. The mouth hooks associated with the cyclorrhaphan cephaloskeleton provide anchorage in the substrate.

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      Review text

      This paper is a huge work on comparison the morphology of head structures in the larvae and adults of the lower Diptera. The study is descriptive and it is extremely complete. The authors used mostly a many data sets from own previous papers and other authors. The original achievement of this paper is description several new characters documented in the figures (images), which quality are very good. As a whole this paper is an important contribution to evolution of lower Diptera. It seems to me also, generally, is very well written and it represent a valuable review on the subject (but I’m not a specialist in dipteran field). This exhaustive review will be of utility for other researchers and for future phylogenetic studies on the group.
      Materials and Methods, and References are correctly and exhaustive prepared. Generally the all paper is precisely formed.
      Overall, as a reviewer I have no reason to suggest any major changes.
      Minor comments:
      1. The author discuss the morphological characters in a phylogenetic perspective. This parts, in my opinion, is not very clear. The authors should consider, in all presented trees also the outgroups, not only in the fig 1C. These outgroups are mentioned in the table 1 and 2 and in the appendix 1 and 2, but they are not included in the cladograms.
      Essentially in the Tree1 A and B the outgroups are not analyzed, so they arrangement and relationships of the taxa are not compatibility with C.
      2. In the figure 2 (page 6) the "potential apomorphies" should be evaluated as the synapomorphies and autapomorphies for the taxa.
      3. The groundplan is made incomprehensible - say clearly what do you understand under"groundplan" (GP) of Diptera head. Generally, GP includes the total of plesiomorphic characters states observed among the species of a group but also the sum of its autapomorphies (of Diptera = synapomorphies of all lower dipteran families) as well the sum of inclusive apomorphic homoplasies shared by all the group.
      In present paper the "apomorphy groundplan" of head is presented as separate parts for larvae and adults and several apomorphic characters are mentioned in different sentences/lines. It seems necessary to summarized this groundplan e.g., in the table, the more so that the aim of this paper is indicated the "reconstruction of the ordinal groundplan"


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