(subphylum Echinozoa, class Echinoidea)
An order of irregular echinoids that have petaloid ambulacra on the upper surface. The periproct is outside the apical system. There are large pores and swellings around the peristome, and no jaws or gill slits. The Cassiduloida first appeared in the Jurassic.
Subjects: Zoology and Animal Sciences.