Inclusive taxon sampling suggests a single, stepwise origin of ectolecithality in Platyhelminthes

摘要: Ectolecithality is a form of oogenesis unique within Metazoa but common in Platyhelminthes, which almost yolkless oocytes and tightly associated yolk cells are deposited together egg capsules. Despite profound impacts on the embryogenesis morphology its beneficiaries, origins this developmental phenomenon remain obscure. Traditionally, all ectolecithal flatworms were grouped clade called Neoophora. However, there also morphological arguments for multiple ectolecithality and, to date, Neoophora has seen little support from molecular phylogenetic research, largely as result gaps taxon sampling. Accordingly, we present phylogeny focused resolving deepest divergences among free-living Platyhelminthes. Species chosen completely span diversity major endo- clades, including several aberrant species uncertain systematic affinity additionally, thorough sampling ‘lecithoepitheliate’ higher taxa Prorhynchida Gnosonesimida, respectively, under- unrepresented phylogenies date. Our analyses validate monophyly classical platyhelminth taxa, resolve possessing distinct yolk-cell oocyte generating organs (which name Euneoophora new taxon). Furthermore, implied-weights parsimony Bayesian mixture model suggest ancestry with lecithoepitheliates, implying that these may retain primitive ectolecithality. This topology thus corroborates hypothesis homology between Neoophora, should serve guide future evolutionary research innovation Platyhelminthes. © 2014 The Linnean Society London, Biological Journal Society, 2014, 111, 570–588.