The Echinoid Directory

Order Arbacioida Gregory, 1900, p. 307

[ex Arbacina Gregory, 1900, p. 307]

Diagnosis	Echinacea with: apical disc small (much smaller than the peristome), dicyclic (rarely hemicyclic); periproct margin smoothly rounded; enclosing periproct ambulacra and interambulacral tubercles small and similar in size; imperforate and non-crenulate in all but the basalmost members; plate compounding in arbaciid or goniopygid style, with at least one demiplate; Basicoronal plate present in interambulacral zones.
Range	Middle Jurassic to Recent, worldwide.
Type	Arbacia
Species Included	This order includes the following families: Acropeltidae, Arbaciidae and Glypticidae. There are also a number of primitive genera that probably belong here as they have a single large basicoronal plate to interambulacral zones (Dubarechinus, Magnosia, Eucosmus).
Classification and/or Status	Euechinoidea, Acroechinoidea, Carinacea, Echinacea
Remarks	The order is distinguished from other Echinacea by its retention of a basicoronal plate in interambulacral zones and in by its characteristic plate compounding. It includes Eucosmechinae Lambert & Thiery, 1911, p. 269. Gregory, J. W. 1900. The Echinoidea, in E. R. Lankester (ed.) A Treatise on Zoology. Part III, the Echinodermata. Adam & Charles Black, London.