{{Short description|Extinct genus of molluscs}} {{Italic title}} {{Speciesbox | genus = Kulindroplax | image = Kulliaporax.png | species = perissokomos | fossil_range = {{Fossil range|Wenlock}} | authority = Sutton, Briggs, Siveter, Siveter and Sigwart, 2012 | parent_authority = Sutton, Briggs, Siveter, Siveter and Sigwart, 2012<ref name="Sutton2012">{{Cite journal | last1 = Sutton | first1 = M. D. | last2 = Briggs | first2 = D. E. G. | author-link2 = Derek Briggs | last3 = Siveter | first3 = D. J. | last4 = Siveter | first4 = D. J. | last5 = Sigwart | first5 = J. D. | title = A Silurian armoured aplacophoran and implications for molluscan phylogeny | doi = 10.1038/nature11328 | journal = Nature | volume = 490 | issue = 7418 | pages = 94–97 | year = 2012 | pmid = 23038472| bibcode = 2012Natur.490...94S | s2cid = 4422386 }}</ref> }}
'''''Kulindroplax perissokomos''''' is a Silurian mollusk, known from a single fossil from the Coalbrookdale Formation fauna of England. It lived during the Homerian Age (about 425 million years ago).<ref name="Sutton2012"/> It is considered a basal aplacophoran. Unlike all modern aplacophorans, which are shell-less, ''Kulindroplax'' has a chiton-like shell, and it is considered a transitional fossil in the evolution of molluscs.<ref name="yalenews">{{cite web|title=Ancient mollusk tells a contrary story|date=3 October 2012 |url=https://news.yale.edu/2012/10/03/ancient-mollusk-tells-contrary-story|publisher=Yale News|access-date=17 November 2012}}</ref><ref name=ucl>{{cite web|title=Mollusc missing link revealed in 3D|date=3 October 2012 |url=http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_3-10-2012-18-20-12|publisher=Imperial College London|access-date=17 November 2012}}</ref>
The only known specimen, described in 2012, was conserved at the Oxford University Museum of Natural History.<ref name="Sutton2012"/>
==Morphology== ''Kulindroplax'' is about {{convert|2|cm|in|abbr=on}} wide and {{convert|4|cm|in|abbr=on}} long.<ref name="yalenews"/> It is the first known mollusk showing an unambiguous combination of valves, or exterior shells, and a worm-like body.<ref name="yalenews"/> It bears seven similar, unarticulated valves, with a shorter head valve and a taller caudal one, lacking ornaments<ref name="Sutton2012"/> and also several densely packed, {{Nowrap|1–2 mm}} long spicules. It has no discernible foot,<ref name="Sutton2012"/> and the radula is not preserved.<ref name="Sutton2012"/> A gill array is present, along with a respiratory cavity opening posteriorly. These features make it more reminiscent of caudofoveate aplacophorans.<ref name="Sutton2012"/>
While aculiferan mollusks usually bear eight dorsal valves (except for multiplacophorans and ''Acaenoplax''), ''Kulindroplax'' bears only seven in a single chiton-like row.<ref>{{Cite journal |last1=Scherholz |first1=Maik |last2=Redl |first2=Emanuel |last3=Wollesen |first3=Tim |last4=Todt |first4=Christiane |last5=Wanninger |first5=Andreas |date=November 2013 |title=Aplacophoran Mollusks Evolved from Ancestors with Polyplacophoran-like Features |journal=Current Biology |language=en |volume=23 |issue=21 |pages=2130–2134 |doi=10.1016/j.cub.2013.08.056 |pmc=3898471 |pmid=24139743|bibcode=2013CBio...23.2130S }}</ref>
==Life habits== ''Kulindroplax'' seems adapted to moving through a substrate, with the spicules acting as "sediment ratchets".<ref name="Sutton2012"/> In contrast with some modern aplacophorans like the caudofoveates, which live within the sea bottom sediments, ''Kulindroplax'' probably crawled on the bottom, requiring a dorsal armour.<ref name="Sutton2012"/>
==Evolutionary significance== ''Kulindroplax'' settles a 20-year-long dispute about the phylogeny of mollusks, namely the relationship of the worm-like, carnivorous Aplacophora within the group, in particular their relationship to the Polyplacophora.<ref name="ucl"/> Aplacophorans have been historically variously treated as either a mollusk base-group, distant relatives of Cephalopoda or as a sister group to Polyplacophora in the clade Aculifera.<ref name="Sutton2012"/> Both molecular and fossil evidence appeared to support the last hypothesis.<ref name="kocot2011">{{Cite journal | last1 = Kocot | first1 = K. M. | last2 = Cannon | first2 = J. T. | last3 = Todt | first3 = C. | last4 = Citarella | first4 = M. R. | last5 = Kohn | first5 = A. B. | last6 = Meyer | first6 = A. | last7 = Santos | first7 = S. R. | last8 = Schander | first8 = C. | last9 = Moroz | first9 = L. L. | last10 = Lieb | first10 = Bernhard | last11 = Halanych | first11 = Kenneth M. |display-authors=9| doi = 10.1038/nature10382 | title = Phylogenomics reveals deep molluscan relationships | journal = Nature | volume = 477 | issue = 7365 | pages = 452–456 | year = 2011 | pmid = 21892190| pmc = 4024475| bibcode = 2011Natur.477..452K }}</ref><ref name="sigwart2007">{{Cite journal| last1 = Sigwart | first1 = J. D.| last2 = Sutton | first2= M. D.| title = Deep molluscan phylogeny: synthesis of palaeontological and neontological data| journal = Proceedings of the Royal Society B: Biological Sciences| issue = 1624| volume = 274| pages = 2413–2419| date =Oct 2007| pmid = 17652065| pmc = 2274978| doi = 10.1098/rspb.2007.0701}} For a summary, see {{cite web| title=The Mollusca | publisher=University of California Museum of Paleontology| url=https://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php| access-date=2 October 2008}}</ref><ref name="scheltema1993">{{cite journal|jstor=1542380|last=Scheltema|first=A.H.|title=Aplacophora as Progenetic Aculiferans and the Coelomate Origin of Mollusks as the Sister Taxon of Sipuncula|journal=The Biological Bulletin|date=February 1, 1993|volume=184|issue=1|pages=57–78|doi=10.2307/1542380|pmid=29300613|url=https://www.biodiversitylibrary.org/part/37201 }}</ref><ref name="vinther2012">{{Cite journal | last1 = Vinther | first1 = J. | last2 = Sperling | first2 = E. A. | last3 = Briggs | first3 = D. E. G. | author-link3 = Derek Briggs | last4 = Peterson | first4 = K. J. | title = A molecular palaeobiological hypothesis for the origin of aplacophoran molluscs and their derivation from chiton-like ancestors | journal = Proceedings of the Royal Society B: Biological Sciences | year = 2011 | doi = 10.1098/rspb.2011.1773 | volume=279 | issue = 1732 | pages=1259–1268 | pmid=21976685 | pmc=3282371}}</ref><ref name="smith2011">{{Cite journal | last1 = Smith | first1 = S. A. | last2 = Wilson | first2 = N. G. | last3 = Goetz | first3 = F. E. | last4 = Feehery | first4 = C. | last5 = Andrade | first5 = S. N. C. S. | last6 = Rouse | first6 = G. W. | last7 = Giribet | first7 = G. | last8 = Dunn | first8 = C. W. | doi = 10.1038/nature10526 | title = Resolving the evolutionary relationships of molluscs with phylogenomic tools | journal = Nature | volume = 480 | issue = 7377 | pages = 364–367 | year = 2011 | pmid = 22031330| bibcode = 2011Natur.480..364S | s2cid = 4321076 }}</ref> Including ''Kulindroplax'' in a phylogenetic matrix with other mollusks and mollusk-like fossil taxa allows to consistently resolve Aculifera as a sister group to Conchifera, in all variants of the analysis, thus bringing the fossil record in line with the recent molecular evidence.<ref name="Sutton2012"/>
While other fossil taxa like ''Acaenoplax'' and ''Phthipodochiton'' showed intermediate features between aplacophorans and polyplacophorans, no unambiguous fossil with an aplacophoran-like body and a polyplacophoran-like shell has been found before ''Kulindroplax''.
Below is a cladogram of mollusk phylogeny according to Sutton ''et al.'', 2012.<ref name="Sutton2012"/> Taxa marked with † are extinct. {{Clear}}
{{Clade|style=font-size:.8em;line-height:75% |label1=← Lophotrochozoa |1={{clade |label1= |1= Brachiopoda |2={{clade |label1= |1=''Odontogriphus''† |label2= |2=Halwaxiids† |label3=Mollusca |3={{clade |label1= |1=Conchifera |label2=Aculifera |2={{clade |label1=Polyplacophora |1={{clade |label1= |1=''Echinochiton''† |label2= |2=Neoloricata }} |label2=Aplacophora |2={{clade |label1= |1=''Epimenia'' |label2= |2=''Septemchiton''† |label3= |3={{clade |label1= |1=''Chaetoderma'' |label2= |2={{clade |label1= |1=''Phthipodochiton''† |label2= |2={{clade |label1= |1='''''Kulindroplax'''''† |label2= |2={{clade |label1= |1=''Acaenoplax''† |label2= |2=''Matthevia''† }} }} }} }} }} }} }} }} }} }}
==References== {{Reflist|32em}}
{{Taxonbar|from=Q6443023}}
Category:Monotypic prehistoric mollusc genera Category:Aplacophorans Category:Silurian molluscs Category:Transitional fossils Category:Wenlock series fossils Category:Silurian animals of Europe