These are echinoderms which are more or less permanently attached to the
bottom of the sea by means of a stalk which is composed of slightly
movable, calcareous, disk-like segments (fig. 23).
Pelmatozoans range from Cambrian to Recent in age, and their fossilized
remains are particularly abundant in Paleozoic rocks. The subphylum has
been divided into several classes, but only three of these, the
Cystoidea, Blastoidea, and Crinoidea, are discussed here. With the
exception of the Crinoidea, all of the attached echinoderms are extinct.