Why Williamson’s (2014) theory of hybridogenesis fails to explain the evolution of the Rhizocephala

in Crustaceana
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All available biological, ultrastructural, and molecular data support the conclusion that the cirripedian suborders, Rhizocephala and Thoracica, are closely related. Williamson’s speculations (Williamson, D. I., 2014. The origin of barnacles (Thecostraca, Cirripedia). Crustaceana, 87: 755-765) that the so-called hybridogenesis can explain how Rhizocephala evolved, rest on a selective choice of other authors’ data and an ignorance of solid facts derived from decades of comparative anatomical and molecular studies.

Why Williamson’s (2014) theory of hybridogenesis fails to explain the evolution of the Rhizocephala

in Crustaceana



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    Moult stages in a representative sacculinid (Polyascus polygenea Glenner, Lützen & Takahashi, 2003): A-E, young, immature individuals (some of them have windows cut out in the mantle to display the mantle cavity and visceral mass); F-G, mature specimens (in G with ovisacs in the mantle cavity). Legends: a1-a4, annuli resulting from and corresponding to moulting of the external mantle cuticles c1-c5; cm, shed cuticle of the interior mantle cavity.

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    Ultrastructure of gland cells producing the ovisac in: A, Semibalanus balanoides (Linnaeus, 1767); and B, Sacculina carcini (Thompson, 1836). [After Walker, 1980, and Lange, 2002, respectively; both reproduced with permission.]

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    Bayesian tree inferred from amino acid sequences data set Pro27T of the Arthropoda. The position of Cirripedia and the sistergroup relationship between Thoracica and Rhizocephala found in the tree is consistent with other molecular phylogenetic analyses of DNA sequences from the last two decades. After Yan et al., 2012; reproduced with permission. This figure is published in colour in the online edition of this journal, which can be accessed via http://booksandjournals.brillonline.com/content/journals/15685403.

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