Pentremites godoni   scale in cms CLASS - Blastoidea ORDER - Spiraculata FAMILY - Pentremitidae GENUS/SPECIES - Pentremites godoni ROCK UNIT - Paint Creek Formation AGE - latest Mississippian (325 million years old) LOCALITY - Floraville, Illinois, USA Pictured above are three thecae (main body portions) of Pentremites. Pentremites is the prototypical blastoid, an extinct group of stemmed echinoderms roughly resembling small crinoids. Blastoids had relatively large, rigid thecae and small stems (note the tiny circular stem attachment surface on the base of the specimen on the left). Simple arms lined the star-shaped grooved area (ambulacra) leading to the mouth (central top). Pentremites is an index fossil for rocks of Mississippian (Early Carboniferous) age in North America. PRI 43590