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17x12x12 mm. A group of extinct echinoderms. Among them are sea urchins (echinoids), sea lilies (crinoids), starfish (asteroids), and brittlestars (ophiuroids).
Fossil echinoderms range back to the Cambrian. Blastoids looked like stemmed crinoids but did not have arms.
Pentremites sp., Mississippian
Millstadt, Illinois, USA
Paint Creek Formation |
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