Here we offer a Blastoid of the species Pentremites symmetricus from the Carboniferus (Mississippian) of Illinois. The Blastoids of the Ridenhower Fm. are relatively common and mostly well preserved.
Blastoids are often discriped as ancient crinoids what is just incorrect. The group of Blastoidea are only indirectly related to the Crinoidea. They are both Echinoderms with a similar life habit and that it nearly is. However the first Blastoids are been found in the Silurian age, they extinct together with many other groups in the end of the Permian age.