Phylogenetic reconstruction of hexapod basal clades : Comparative embryological analyses of entognathy formations of all three entognathan constituents

近年来，内颚类-外颚类系统受到了挑战，内颚类的序间关系和单系性受到了多方面的质疑。内颌型被认为是内颌类最可靠的自形。我比较了原尾目、弹尾目和双尾目的内颚结构，研究了它们的内颚结构的同源性，并讨论了内颚目的序间关系和单系性。原尾目和弹尾目在内颚结构的主要方面彼此非常相似，例如：1）口褶的起源，口褶是由中间背片和三个颚段的延伸融合形成的; 2）内颌后区的起源，其来源于唇背向内侧迁移并联合。然而，双尾目的内颌结构是以不同的方式构造的，其特征在于：1）口褶是由间颚节和三颚节的延伸背与唇基融合而成; 2）内颚后区是由唇基亚基向内侧迁移并联合成颏后区而成; 3）唇侧附肢的旋转参与了内颌的形成。因此，原尾目和弹尾目的内颚类的同源性得到了很好的支持，从而支持了椭圆尾目的单系性。虽然双尾类的内颚形成方式与原尾类和弹尾类也有很大不同，但原尾-弹尾类与双尾类之间的内颚形成的同源性并不总是得到证实，内颚类的单系性也不能得到证实。

Recently, Entognatha-Ectognatha System has been challenged, and doubt has been cast on the interordinal relationships within and monophyly of Entognatha from multiple sources. Entognathy has been regarded as a most reliable autapomorphy of Entognatha. I compare the entognathy formations of Protura, Collembola and Diplura, examine the homology of their entognathies, and discuss the interordinal relationships and monophyly of Entognatha.Protura and Collembola are revealed to closely resemble each other in major points of entognathy formation, such as concerning : 1) the origin of mouth folds, which are formed by the extension and fusion of terga of intercalary and three gnathal segments, and 2) origin of the postgnathal region of entognathy, which is derived from labial terga medially migrated and united. However, the entognathy of Diplura is constructed in a different manner, which is characterized by : 1) the mouth fold is formed by the fusion of extended terga of intercalary and three gnathal segments and labial coxa, 2) the postgnathal region of entognathy is derived from labial subcoxae which medially migrate and unite into a form of postmentum, and 3) the rotation of labial appendages is involved in the entognathy formation. Thus, the homology of entognathy is well supported between Protura and Collembola, hence the monophyly of Ellipura may be supported. While the manner of entognathy formation in Diplura is revealed to be much different from in Protura and Collembola either, hence the homology of entognathy between Protura-Collembola and Diplura is not always verified, and the monophyly of Entognatha could not be substantiated.