Class of extinct marine echinoderms that existed from the Ordovician to Permian periods, but were particularly abundant in the early Carboniferous period. Blastoids were stemless or short-stemmed suspension-feeders with a budlike skeleton made of relatively few symmetrically arranged calcareous plates. They possessed an elaborate system of enclosed canals, or hydrospires, which probably served a respiratory function. Pentremites are an example, found abundantly in early Carboniferous limestone.

Classification
Blastoidea is in phylum Echinodermata.