title: The continuing debate on deep molluscan phylogeny: evidence for Serialia (Mollusca, Monoplacophora + Polyplacophora).
abstract: Molluscs are a diverse animal phylum with a formidable fossil record. Although there is little doubt about the monophyly of the eight extant classes, relationships between these groups are controversial. We analysed a comprehensive multilocus molecular data set for molluscs, the first to include multiple species from all classes, including five monoplacophorans in both extant families. Our analyses of five markers resolve two major clades: the first includes gastropods and bivalves sister to Serialia (monoplacophorans and chitons), and the second comprises scaphopods sister to aplacophorans and cephalopods. Traditional groupings such as Testaria, Aculifera, and Conchifera are rejected by our data with significant Approximately Unbiased (AU) test values. A new molecular clock indicates that molluscs had a terminal Precambrian origin with rapid divergence of all eight extant classes in the Cambrian. The recovery of Serialia as a derived, Late Cambrian clade is potentially in line with the stratigraphic chronology of morphologically heterogeneous early mollusc fossils. Serialia is in conflict with traditional molluscan classifications and recent phylogenomic data. Yet our hypothesis, as others from molecular data, implies frequent molluscan shell and body transformations by heterochronic shifts in development and multiple convergent adaptations, leading to the variable shells and body plans in extant lineages.
authors.affiliation: SNSB-Bavarian State Collection of Zoology, Münchhausenstraße 21, 81247 Munich, Germany ; Faculty of Biology, Department II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Stöger
authors.affiliation: Queen's University Belfast, School of Biological Sciences, Marine Laboratory, 12-13 The Strand, Portaferry BT22 1PF, UK.
authors.forename: J D
authors.initials: JD
authors.lastname: Sigwart
authors.affiliation: Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kano
authors.affiliation: Senckenberg Research Institute, German Centre for Marine Biodiversity Research (DZMB), Südstrand 44, 26382 Wilhelmshaven, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Knebelsberger
authors.affiliation: Museum of New Zealand Te Papa Tongarewa, P.O. Box 467, Wellington, New Zealand.
authors.forename: B A
authors.initials: BA
authors.lastname: Marshall
authors.affiliation: SNSB-Bavarian State Collection of Zoology, Münchhausenstraße 21, 81247 Munich, Germany ; Faculty of Biology, Department II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Schwabe
authors.affiliation: SNSB-Bavarian State Collection of Zoology, Münchhausenstraße 21, 81247 Munich, Germany ; Faculty of Biology, Department II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schrödl
mesh_terms: D000818:Animals; D005580:Fossils; D008974:Mollusca / Q000145:classification* / Q000235:genetics*; D010802:Phylogeny; D049916:Polyplacophora / Q000145:classification* / Q000235:genetics*