Crinoid

Macrocrinus mundulus

• Mississippian
• Edwardsville Formation
• Crawfordsville, Indiana, USA

Size: 6 cm crown including anal sac

My first crinoid fossil and one of my first fossils, period. This species is the most common of the Crawfordsville crinoids and a good representative of monobathrid camerates, which were prevalent during the Mississippian. Note the elongated anal tube poking out above the arms, which is considered to be an adaptation to defend against parasitic gastropods.