(or sea buds), a class of extinct invertebrate animals of the phylum Echinodermata. The body of the blastoid consisted of a crown formed by a blastoid calyx, or theca, with numerous “arms,” or brachioles, and a stem. The brachioles caught particles of food, which were directed to the mouth along sulci, or grooves, running from the brachioles to the ambulacra. Under the surface of the calyx was a system of calcareous tubes (hydrospires), which probably served for breathing. Blastoidea lived in the oceans from the Silurian to the Permian period. They were numerous in the Devonian and Early Carboniferous periods in North America and in the Permian period in Indonesia and the Ural Region. More than 300 species of Blastoidea are known. Some of them are the leading fossils of the Carboniferous and Permian periods.