<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 8.00.6001.18928">
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff><FONT size=2 face=Arial>
<DIV class=article-heading>
<DL class=citation>
<DT>Nature</DT>
<DT class=volume>Volume: 490<SPAN>, </SPAN>Pages: 94–97</DT>
<DT>Published online 03 October 2012</DT></DL></DIV>
<DIV class=article-heading> </DIV>
<DIV class=article-heading><FONT size=4>A Silurian armoured aplacophoran and
implications for molluscan phylogeny</FONT></DIV>
<DL class=citation>
<DT>The Mollusca is one of the most diverse, important and well-studied
invertebrate phyla; however, relationships among major molluscan taxa have
long been a subject of controversy<SUP><A id=ref-link-1
title="Kocot, K. M. et al. Phylogenomics reveals deep molluscan relationships. Nature 477, 452-456 (2011)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref1">1</A>,
<A id=ref-link-2
title="Wilson, N. G., Rouse, G. W. & Giribet, G. Assessing the molluscan hypothesis Serialia (Monoplacophora + Polyplacophora) using novel molecular data. Mol. Phylogenet. Evol. 54, 187-193 (2010)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref2">2</A>,
<A id=ref-link-3
title="Giribet, G. et al. Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons. Proc. Natl Acad. Sci. USA 103, 7723-7728 (2006)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref3">3</A>,
<A id=ref-link-4
title="Passamaneck, Y. J., Schander, C. & Halanych, K. M. Investigation of molluscan phylogeny using large-subunit and small-subunit nuclear rRNA sequences. Mol. Phylogenet. Evol. 32, 25-38 (2004)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref4">4</A>,
<A id=ref-link-5
title="Sigwart, J. D. & Sutton, M. D. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proc. R. Soc. B 274, 2413-2419 (2007)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref5">5</A>,
<A id=ref-link-6
title="Salvini-Plawen, L. & Steiner, G. in Origin and Evolutionary Radiation of the Mollusca (ed. Taylor, J. D.), Ch. 2 29-51 (Oxford Univ. Press, 1996)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref6">6</A>,
<A id=ref-link-7
title="Scheltema, A. H. Aplacophora as progenetic aculiferans and the coelomate origin of mollusks as the sister taxon of Sipuncula. Biol. Bull. 184, 57-78 (1993)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref7">7</A>,
<A id=ref-link-8
title="Salvini-Plawen, L. On the phylogenetic significance of the aplacophoran Mollusca. Iberus 21, 67-97 (2003)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref8">8</A>,
<A id=ref-link-9
title="Telford, M. J. & Budd, G. E. Invertebrate evolution: bringing order to the molluscan chaos. Curr. Biol. 21, R964-R966 (2011)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref9">9</A></SUP>.
In particular, the position of the shell-less vermiform Aplacophora and its
relationship to the better-known Polyplacophora (chitons) have been
problematic: Aplacophora has been treated as a paraphyletic or monophyletic
group at the base of the Mollusca<SUP><A id=ref-link-10
title="Giribet, G. et al. Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons. Proc. Natl Acad. Sci. USA 103, 7723-7728 (2006)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref3">3</A>,
<A id=ref-link-11
title="Salvini-Plawen, L. & Steiner, G. in Origin and Evolutionary Radiation of the Mollusca (ed. Taylor, J. D.), Ch. 2 29-51 (Oxford Univ. Press, 1996)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref6">6</A>,
<A id=ref-link-12
title="Salvini-Plawen, L. On the phylogenetic significance of the aplacophoran Mollusca. Iberus 21, 67-97 (2003)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref8">8</A></SUP>,
proximate to other derived clades such as Cephalopoda<SUP><A id=ref-link-13
title="Wilson, N. G., Rouse, G. W. & Giribet, G. Assessing the molluscan hypothesis Serialia (Monoplacophora + Polyplacophora) using novel molecular data. Mol. Phylogenet. Evol. 54, 187-193 (2010)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref2">2</A>,
<A id=ref-link-14
title="Giribet, G. et al. Evidence for a clade composed of molluscs with serially repeated structures: monoplacophorans are related to chitons. Proc. Natl Acad. Sci. USA 103, 7723-7728 (2006)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref3">3</A>,
<A id=ref-link-15
title="Meyer, A., Witek, A. & Lieb, B. Selecting ribosomal protein genes for invertebrate phylogenetic inferences: how many genes to resolve the Mollusca? Methods Ecol. Evol. 2, 34-42 (2011)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref10">10</A></SUP>,
or as sister group to the Polyplacophora, forming the clade Aculifera<SUP><A
id=ref-link-16
title="Kocot, K. M. et al. Phylogenomics reveals deep molluscan relationships. Nature 477, 452-456 (2011)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref1">1</A>,
<A id=ref-link-17
title="Sigwart, J. D. & Sutton, M. D. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proc. R. Soc. B 274, 2413-2419 (2007)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref5">5</A>,
<A id=ref-link-18
title="Scheltema, A. H. Aplacophora as progenetic aculiferans and the coelomate origin of mollusks as the sister taxon of Sipuncula. Biol. Bull. 184, 57-78 (1993)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref7">7</A>,
<A id=ref-link-19
title="Vinther, J., Sperling, E. A., Briggs, D. E. G. & Peterson, K. A molecular palaeobiological hypothesis for the origin of aplacophoran molluscs and their derivation from chiton-like ancestors. Proc. R. Soc. B 279, 1259-1268 (2012)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref11">11</A>,
<A id=ref-link-20
title="Smith, S. A. et al. Resolving the evolutionary relationships of molluscs with phylogenomic tools. Nature 480, 364-367 (2011)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref12">12</A></SUP>.
Resolution of this debate is required to allow the evolutionary origins of
Mollusca to be reconstructed with confidence. Recent fossil finds<SUP><A
id=ref-link-21
title="Sutton, M. D., Briggs, D. E. G., Siveter, J. & Siveter, J. An exceptionally preserved vermiform mollusc from the Silurian of England. Nature 410, 461-463 (2001)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref13">13</A>,
<A id=ref-link-22
title="Sutton, M. D., Briggs, D. E. G., Siveter, J. & Siveter, J. Computer reconstruction and analysis of the vermiform mollusc Acaenoplax hayae from the Herefordshire Lagerstatte (Silurian, England), and implications for molluscan phylogeny. Palaeontology 47, 293-318 (2004)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref14">14</A>,
<A id=ref-link-23
title="Vendrasco, M. J., Wood, T. E. & Runnegar, B. N. Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons. Nature 429, 288-291 (2004)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref15">15</A>,
<A id=ref-link-24
title="Sutton, M. D. & Sigwart, J. D. A chiton without a foot. Palaeontology 55, 401-411 (2012)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref16">16</A></SUP>
support the Aculifera hypothesis, demonstrating that the Palaeozoic-era
palaeoloricate ‘chitons’ included taxa combining certain polyplacophoran and
aplacophoran characteristics<SUP><A id=ref-link-25
title="Sigwart, J. D. & Sutton, M. D. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proc. R. Soc. B 274, 2413-2419 (2007)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref5">5</A></SUP>.
However, fossils combining an unambiguously aplacophoran-like body with
chiton-like valves have remained elusive. Here we describe such a fossil,
<I>Kulindroplax perissokomos</I> gen. et sp. nov., from the Herefordshire
Lagerstätte<SUP><A id=ref-link-26
title="Briggs, D. E. G., Siveter, J. & Siveter, J. Soft-bodied fossils from a Silurian volcaniclastic deposit. Nature 382, 248-250 (1996)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref17">17</A>,
<A id=ref-link-27
title="Briggs, D. E. G., Siveter, J., Siveter, J. & Sutton, M. D. Virtual fossils from a 425 million-year-old volcanic ash. Am. Sci. 96, 474-481 (2008)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref18">18</A></SUP>
(about 425 million years <SPAN class=scp>bp</SPAN>), a Silurian deposit
preserving a marine biota<SUP><A id=ref-link-28
title="Briggs, D. E. G., Siveter, J., Siveter, J. & Sutton, M. D. Virtual fossils from a 425 million-year-old volcanic ash. Am. Sci. 96, 474-481 (2008)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref18">18</A></SUP>
in unusual three-dimensional detail. The specimen is reconstructed
three-dimensionally through physical–optical tomography<SUP><A id=ref-link-29
title="Sutton, M. D. Tomographic techniques for the study of exceptionally preserved fossils. Proc. R. Soc. B 275, 1587-1593 (2008)"
href="http://www.nature.com/nature/journal/v490/n7418/full/nature11328.html#ref19">19</A></SUP>.
Phylogenetic analysis indicates that this and many other palaeoloricate
chitons are crown-group aplacophorans.</DT></DL></FONT></BODY></HTML>