Blastoids, commonly called "sea buds," were a subclass of the class Cystoidea in the phylum Echinodermata. They first appeared in the Ordovician, flourished during the Mississippian, and died out toward the end of the Permian period. A protective calcium carbonate shell surrounded the blastoid's head, or theca, and a plated stalk connected it to the sea floor.

Courtesy of Creative Commons; photo by James St. John