RECONSTRUCTION OF HEXAPOD PHYLOGENY BASED ON THE EVOLUTIONARY TRANSITION OF EMBRYONIC MEMBRANES: EMBRYOLOGICAL STUDY ON DIPLURA

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One of the most controversial problems in hexapod phylogeny concerns the Diplura. In this research project, I extend a phylogenetic discussion involving Diplura, in the light of the scheme 'the evolutionary changes of embryonic membranes and the specialization between the embryo proper and embryonic membranes in hexapods and allied arthropods' that I have developed and demonstrated.I critically examined the dipluran embryogenesis with special reference to the development of embryonic membranes and related phenomena. The following results were deduced : 1) the cuticular egg envelope of Diplura is derived both from the embryo proper and serosa, to be categorized in the blastoderm cuticle ; 2) a homologue of the amnion, which has been regarded as an embryological autapomorphy of Ectognatha, develops in Diplura ; and 3) any structures comparable to the amnioserosal fold are not formed, in spite of the production of amnion, in Diplura.These results obtained can be read, in the context of 't … More he evolutionary changes of embryonic membranes and the specialization between the embryo proper and embryonic membranes in hexapods and allied arthropods', as follows : 1) the production of blastoderm cuticle in Diplura is to be recognized as being plesiomorphic within hexapods ; 2) the production of amnion can be designated as a synapomorphy of Diplura and Ectognatha ; and 3) it is not the production of amnion but the formation of amnioserosal folds as well as the linkage of amniotic production to the formation of fold, that should be nominated as the autapomorphy of Ectognatha, were precisely Dicondylia. Consequently, proposed is a phylogeny formulated as : Hexapoda = Collembola + (Diplura + Ectognatha (= Archaeognatha + Dicondylia (= Zygentoma + Pterygota))). This requires a substantial revision to the currently accepted hexapod phylogeny formulated as : Hexapoda = Entognatha (= Collembola + Diplura) + Ectognatha (= Archaeognatha + Dicondylia (= Zygentoma + Pterygota)), rejecting a monophyletic status of Entognatha. It is verified as well that the scheme I have argued concerning 'the evolutionary changes of embryonic membranes and the specialization between the embryo proper and embryonic membranes in hexapods and allied arthropods' does not need to be revised, even if either Crustacea or Myriapoda showing the sister relationship to Hexapoda. Less