The Echinoid Directory

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Subclass Acroechinoidea Smith, 1981, p. 170

Diagnosis	Euechinoids with: five or fewer pairs of ambulacral plates on the peristomial membrane test plating more or less firmly sutured together, not imbricate
Range	Late Triassic to Recent, worldwide
Species Included	Includes all Euechinoidea with the exception of the Echinothurioida, i.e. Carinacea, and four small orders previously grouped together as the Aulodonta (Diadematoida, Micropygoida, Aspidodiadematoida and Pedinoida).
Remarks	Regular echinoid members of this clade are distinguished from Cidaroidea by the presence of ambulacral plate compounding and from Echinothurioida by the presence of a single pair of buccal plates and tube-feet to each ambulacral zone on the peristome. The following taxon is currently too poorly known to place with certainty: Nicolleauma Vadet, 1999 Smith, A. B. 1981. Echinoid Palaeobiology. George Allen & Unwin, London. Kroh, A. & Smith, A. B. 2010. The phylogeny and classification of post-Palaeozoic echinoids. Journal of Systematic Palaeontology 8, 147-212.