Cystoids and Blastoids: Primitive Stalked Marine Animals (PA-10)
Cystoids and blastoids, extinct relatives of modern starfish and sand dollars, flourished about 500 million years ago. Attached to the sea bottom by a flexible stem, their limy-plated bodies were a fraction of an inch to more than 2 inches in diameter. Numerous small tentacles extended from their heads to capture microscopic food particles from sea water.

Fossil blastoids are found in the Silurian Osgood Shale in southeastern Indiana. Fossil cystoids have been collected from ancient Silurian reefs in northern and central Indiana and Mississippian rocks in south- central Indiana. Blastoids and cystoids lived in communities with crinoids, corals, brachiopods and byozoans.

Our Hoosier State Beneath Us: Paleontology