Cladogram showing some major events in deuterostome evolution.

<p>Relationships of living organisms are based on molecular data (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038296#pone.0038296-Dunn1" target="_blank">[4]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038296#pone.0038296-Osborn1" target="_blank">[8]</a>); fossils are placed using morphological homologies. 1, Dipleurula-type larva and tripartite organization of body coeloms; 2, Multiplated calcite skeleton with stereom microstructure; 3, Complete ctenidial ring; 4, Periproct non-terminal; 5, Water vascular system with single hydropore (asymmetric development of coeloms); 6, Adult body plan not bilateral (associated with larval attachment and torsion during metamorphosis in extant groups); 7, Tentacular feeding; 8, Radial organization of water vascular system.</p

Natural mould and latex casts of the holotype of <i>Ctenoimbricata spinosa</i> gen. et sp. nov. (MPZ 2011/93) in dorsal (A, C) and ventral views (B, D).

<p>Latex casts were whitened with NH₄Cl sublimate.</p

Reconstruction of <i>Ctenoimbricata spinosa</i> gen. et sp. nov.

<p>Reconstruction of <i>Ctenoimbricata spinosa</i> gen. et sp. nov.</p

Radiate and asymmetric echinoderms from the Cambrian showing a selection of primitive echinoderm body plans.

<p><b>A</b>, the ctenocystoid <i>Ctenocystis</i>; <b>B</b>, the cinctan <i>Gyrocystis</i>; <b>C</b>, the helicoplacoid <i>Helicoplacus</i>; <b>D</b>, the solute <i>Coleicarpus</i>; <b>E</b>, the eocrinoid <i>Gogia</i>; <b>F</b>, stromatocystitid edrioasteroid.</p

Fossil locality and geological setting.

<p><b>A</b>, Map of Spain showing the location of the Iberian Chains (IC). <b>B</b>, Map showing the Purujosa locality in the northern part of the Iberian Chains. <b>C,</b> Geological map of Purujosa with indication of the studied section (marked with a star). <b>D</b>, Composite stratigraphic section indicating the level from where <i>Ctenoimbricata spinosa</i> was collected.</p

<i>Ctenoimbricata spinosa</i> gen. et sp. nov. Cambrian Series 3, Stage 5, Purujosa, Spain.

<p>Computer models (<b>A</b>–<b>G</b>, <b>I</b>) and photograph with interpretive camera lucida drawing (<b>H</b>). (<b>A</b>–<b>D</b>, <b>G</b>–<b>I</b>) Holotype MPZ 2011/93. (<b>E</b>, <b>F</b>) Paratype MPZ 2011/94. (<b>A</b>, <b>B</b>) Dorsal and ventral views. (<b>C</b>) Oblique left view. (<b>D</b>) Lateral view of two marginal plates showing the articulation of the spines. (<b>E</b>) Marginal frame plates after correction of plate orientations. (<b>F</b>) Suroral plate in dorsal and lateral aspect. (<b>G</b>) Oblique right view with the dorsal ctenidium partially transparent to show the ventral ctenidial plates. (<b>H</b>) Left anterior part of the theca showing the arrangement of the dorsal ctenidial plates. (<b>I</b>) Frontal view. Abbreviations: ds (dorsal spines), icp (imbricate ctenidial plates), Lcp (lower ctenidial plates), LL (adoral left plate), M (marginal plate), RL (adoral right plate), scp (spiny ctenidial plates), sp (suroral plate), ui, li (upper and lower integuments).</p

Diagram showing inferred homologies between ctenocystoids (<i>Ctenocystis</i> and <i>Courtessolea</i>), <i>Ctenoimbricata</i> and cinctans (<i>Sotocinctus</i>).

<p>The upper row illustrates dorsal surfaces, the lower row ventral surfaces; colors indicate plating series that are homologized. Reconstructions of ctenocystoids are modified from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038296#pone.0038296-Cameron1" target="_blank">[34]</a>. S  =  suroral plate; O  =  operculum.</p

Video S1

Results of a CFD simulation using a time-dependent solver to show flow time-evolution. Simulation of passive tentacular feeding with Protocinctus oriented at 180° to the current (ambient velocity of 0.2 m/s) and with the ventral swelling buried within the sediment, visualized as two-dimensional plots (horizontal cross-sections) of flow velocity magnitude (false-colour scale different for each ambient flow velocity) with streamlines over the first 10 s with a time step size of 0.01 s

Model S3

Digitally restored model of Protocinctus (operculum in ‘open’ position) in IGES format, compressed in a ZIP archive. To view, unzip the .zip file and open the unpacked .igs file with FreeCAD (program and documentation available from www.freecadweb.org)

Model_S1

Digital reconstruction of Protocinctus in VAXML format, compressed in a ZIP archive. To view, unzip the .zip file and open the unpacked .vaxml file with SPIERSview (program and documentation available from www.spiers-software.org)