Article: Cambrian eleutherozoan echinoderms and the early diversification of edrioasteroids
Andrew B. Smith
The five genera and thirteen named species of edrioasteroid from the Cambrian are reviewed and, where necessary, redescribed. All are interpreted as sessile suspension feeders, with an external system of radial water vessels and tube feet that functioned in opening the cover plate sheets. The relationships of these five genera to one another and to other edrioasteroid groups is analysed and a revised classification of the Edrioasteroidea is proposed. Stromatocystites has fewest autapomorphic characters and is placed as primitive sister group to the other four genera. These fall into two distinct groups: Totiglobus and Walcottidiscus are rather globular with a reduced dorsal surface, while Cambraster and Edriodiscus are discoidal with a prominent marginal frame. Three orders are recognized within the Edrioasteroidea: the Edrioasterida, which includes Totiglobus, Walcottidiscus, and the family Edrioasteridae; the Cyathocystida, for the families Cyathocystidae and Pyrgocystidae; and the Isorophida, which is expanded to include Cambraster, Edriodiscus, and the families Cyclocystoididae and Agelacrinitidae.