Abstract

In evolution of the Echinocystoidea the test becomes flattened, the ambulacra expand adorally, pores shift from near the perradial suture to near the adradial suture, tubefeet become enclosed, internal enclosures of radial water vessels are lost, number of interambulacral columns increases in some families, the perradial groove is lost, ambulacral plates become more regular in shape, and more numerous except in cidarids, test size increases, the lantern becomes more complex, the spines more differentiated, and tubercles develop. Changes are adaptive; trends indicate phylogeny. New taxa are Pronechinus anatoliensis n. gen. et sp. and Miocidaris connorsi n. sp., both Permian; and Polytaxicidaris lirata n. sp. Hyattechinus laudoni n. sp., Lovenechinus gordoni n. sp., and Palaechinus sprengi n. sp., Mississippian.

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