<p>Pentremites sp. - fossil blastoids from the Mississippian of Kentucky, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA)
</p><p>Blastoids are an extinct group of echinoderms.  They resemble crinoids in having a head, or theca, perched atop a long stem of stacked columnals composed of calcite (see pictures of a complete specimen elsewhere in this photo album).  Crinoids and blastoids are pelmatozoans - stalked echinoderms.  Both groups are sessile, benthic, filter-feeding organisms.  The overall structure and morphology of crinoid heads and blastoid heads are quite different.  Blastoid heads have pentaradial symmetry and somewhat resemble closed flower buds or nuts.  They have 5 ambulacral grooves extending outward and downward from the summit of the theca.  During life, many thin, delicate brachioles extended from the ambulacral grooves - these structures captured tiny particles of food from seawater as the blastoid engaged in filter feeding.
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<hr><p>From exhibit signage:
These "bud-like" structures represent the calyx or theca of an extinct echinoderm group, the blastoids.  Pentremites is certainly the most well known blastoid genus.  These exceptionally large specimens are of Mississippian age from Big Hill, Kentucky.
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<hr><p>Classification: Animalia, Echinodermata, Blastozoa, Blastoidea, Spiraculata, Pentremitidae
</p><p>Stratigraphy: unrecorded/undisclosed, but probably the Slade Formation, Upper Mississippian
</p><p>Locality: unrecorded/undisclosed site at or near Bighill, Kentucky, USA (but possibly from a large Rt. 421 roadcut through Bighill Mountain on the Madison County-Rockcastle County line, south of the town of Bighill)
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<hr><p>More info. at:
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&lt;a href="<a class="external free" href="https://en.wikipedia.org/wiki/Blastoid">https://en.wikipedia.org/wiki/Blastoid</a>" rel="nofollow"&gt;en.wikipedia.org/wiki/Blastoid&lt;/a&gt;
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/27250480468/">Pentremites sp. (fossil blastoids) (Mississippian; Big Hill, Kentucky, USA) 2</a>