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Crinoid

Pirasocrinus scotti

• Pennsylvanian
• Millsap Lake Formation
• Brock, Texas, USA

Size: 7 cm crown

Here is a magnificent pirasocrinid from the Pennsylvanian of Texas. However it is not just any pirasocrinid, but Pirasocrinus scotti, the type-genus and type-species upon which the family Pirasocrinidae was established and named back in 1940. Despite giving the family its name, Pirasocrinus actually appears to be quite unusual and much rarer compared to more typical pirasocrinids such as Plaxocrinus or Stenopecrinus. P. scotti possesses a deep basal concavity, incredibly bulbous axillary brachials with thin tapering spines, and the upper extreme of arm branching for the family, reaching upwards of 80 arms in total (as opposed to Plaxocrinus or Stenopecrinus which typically have 30-40 arms). Unfortunately the spinose anal sac is poorly-preserved on this specimen as is the case for most pirasocrinid fossils, but some of its flat polygonal plates are visible above the arms.

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