Crinoid

Staphylocrinus bulgeri

• Mississippian
• Monteagle Limestone
• Morgan County, Alabama, USA

Size: 6.5 cm crown

Staphylocrinus is a fascinating stemless crinoid similar to the likewise stemless Agassizocrinus. These crinoids appear to have fused their infrabasal plates into singular solid infrabasal disks/cones and detached from their stems during development like modern free-swimming comatulid crinoids, though unlike comatulids they presumably lived a benthic lifestyle on the seafloor. In Staphylocrinus oftentimes the infrabasals show evidence of this process as a scar or depression, and sometimes the remnant stem can even be observed in cross-section (Burdick & Strimple 1969).

Staphylocrinus is distinguished by its bowl-shaped calyx with tumid plates, relatively broad, tumid infrabasals that project below the basals, and multiple branchings in the arms. Its genus name derives from staphylos (Greek) meaning a cluster of grapes, which refers to the appearance of the calyx owing to the tumidity of its plates (Burdick & Strimple 1969). This crinoid is also very rare with a highly-limited stratigraphic range, as it appears to be restricted to the Gasperian Stage of the Chesterian Age of the Mississippian Period.