Perischoechinoidea is a subclass of primitive sea urchins that were abundant in the Palaeozoic seas. However, the great majority of species died out during...

Subphylum: Echinozoa Class: Echinoidea Leske, 1778 Subclasses Subclass Perischoechinoidea Order Cidaroida (pencil urchins) Subclass Euechinoidea Superorder...

order of primitive sea urchins, the only living order of the subclass Perischoechinoidea. All other orders of this subclass, which were even more primitive...

Echinocystitoida were an order of extinct sea urchin in the subclass Perischoechinoidea. Answers.com v t e...