What is "blastoid"

Blastoid \Blas"toid\, n. (Zo["o]l.) One of the Blastoidea. [1913 Webster] ||

a. 1 (context paleontology English) Of or relating to blastoids. 2 (context medicine English) blastic. n. (context paleontology English) A member of an extinct class of echinoderms, the Blastoidea.

Blastoids (class Blastoidea) are an extinct type of stemmed echinoderm. Often called sea buds, blastoid fossils look like small hickory nuts. They first appear, along with many other echinoderm classes, in the Ordovician period, and reached their greatest diversity in the Mississippian subperiod of the Carboniferous period. However, blastoids may have originated in the Cambrian. Blastoids persisted until their extinction at the end of Permian, about 250 million years ago. Although never as diverse as their contemporary relatives, the crinoids, blastoids are common fossils, especially in many Mississippian-age rocks.