Abstract

Disasteroid echinoids are members of the superorder Atelostomata characterized by a disjunct apical system. Recent studies have demonstrated that primitive disasteroids are endocyclic and that the transition to exocyclic forms can be traced in several lineages. The best documentation of the regular-irregular transition is within the Collyritidae. The Disasteridae as previously conceived is polyphyletic because the non-intercalary apical system evolved at least four times. The classification of the Atelostomata is revised to include these orders: Galeropygoida, new; Cassiduloida; Disasteroida, new; Holasteroida; Pourtalesioida, new; Spatangoida. Disasteroida includes the families: Pygorhytidae; Collyritidae; Disasteridae; Tithoniidae, new; Acrolusiidae, new.

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