Crinoid

Paramphicrinus oklahomaensis

• Pennsylvanian
• LaSalle Limestone Member, Bond Formation
• Pontiac, Illinois, USA

Size: 4.5 cm across the arms

Flexible crinoids were unusual during the Pennsylvanian, and Paramphicrinus oklahomaensis is the rarer of the two found in the LaSalle Limestone. At a glance this crinoid seems similar to the commonly-seen Mississippian flexibles such as Taxocrinus and Onychocrinus, but the lack of a distinct anal tube assigns it to the Sagenocrinoidea instead of the Taxocrinoidea. Some other notable features include the arms being tightly incorporated into the calyx via interradial plates, and the arms branching many more times towards the tips (reaching between 80-100 arms in total) where they are strongly incurved. These traits in addition to others give the crown an overall very stout, compact, globe-like form.