Devonian echinoderms

thumb|right|200px|"Blastoidea", from Ernst Haeckel's Art Forms of Nature, 1904

Cystoidea was defined as a class of extinct paleozoic blastozoan echinoderms established to encompass stalked taxa that were neither crinoids nor blastoids. It was shown to be polyphyletic in the late 1960s but continues to be used even in recent (as of 2022) literature to discuss both rhombiferans and diploporitans.

Blastozoa is a subphylum of extinct echinoderms characterized by the presence of specialized respiratory structures and brachiole plates used for feeding. It ranged from the Cambrian to the Permian. Biserial, triradiate, and pentaradiate ambulacral patterns have been identified in blastozoa specimens. The pentaradiate pattern in particular has been associated with several different classes.

Archaeocidaris is an extinct genus of echinoid that lived from the Late Devonian to the Late Permian. Its remains have been found in Africa, Europe, and North America. thumb|left|Archaeocidaris plates and spines from the Bird Spring Formation (Carboniferous) exposed in Kyle Canyon, Spring Mountains, southern Nevada.