Kulindroplax

{{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{{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 }}

}}

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). 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.{{cite web|title=Ancient mollusk tells a contrary story|date=3 October 2012 |url=http://news.yale.edu/2012/10/03/ancient-mollusk-tells-contrary-story|publisher=Yale News|access-date=17 November 2012}}{{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}}

The only known specimen, described in 2012, was conserved at the Oxford University Museum of Natural History.

Morphology

Kulindroplax is about {{convert|2|cm|in|abbr=on}} wide and {{convert|4|cm|in|abbr=on}} long. It is the first known mollusk showing an unambiguous combination of valves, or exterior shells, and a worm-like body. It bears seven similar, unarticulated valves, with a shorter head valve and a taller caudal one, lacking ornaments and also several densely packed, {{Nowrap|1–2 mm}} long spicules. It has no discernible foot, and the radula is not preserved. A gill array is present, along with a respiratory cavity opening posteriorly. These features make it more reminiscent of caudofoveate aplacophorans.

While aculiferan mollusks usually bear eight dorsal valves (except for multiplacophorans and Acaenoplax), Kulindroplax bears only seven in a single chiton-like row.{{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 }}

Life habits

Kulindroplax seems adapted to moving through a substrate, with the spicules acting as "sediment ratchets". 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.

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. 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. Both molecular and fossil evidence appeared to support the last hypothesis.{{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 }}{{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=http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php| access-date=2 October 2008}}{{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 }}{{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}}{{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 }} 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.

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. Taxa marked with † are extinct.

{{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