The Echinoid Directory

 Stem group echinoids with:

• test composed of ambulacral and interambulacral plates; plating thin and strongly imbricate throughout
• apical disc with single genital plate
• ambulacral zones quadriserial; pore-pairs small and undifferentiated
• internal perradial flanges on ambulacral plate enclosing the radial water vessel adorally
• interambulacra composed of up to 10 columns of thin, imbricate, polygonal plates
• no primary tubercle, but several small mamelonate secondary tubercles on interambulacral plates
• spines short and simple.

Upper Silurian to Devonian, Europe.

A more restricted usage of the family is applied here, since many of the taxa included here by Kier (1966) are treated as a separate clade, the Proterocidaridae. Proterocidaridae differ from Echinocystitidae in having large, circular, oral pore-pairs of very distinctive form. In addition their radial water vessel is generally not enclosed by perradial extensions of the ambulacral plates. Echinocystitidae are presumably a plesiomorphic sister group to Proterocidaridae, but a modern analysis of the problem is required.

Kier, P. M. 1966. Noncidaroid Paleozoic echinoids. Pp. U298-U312 in Moore, R. C. (ed.) Treatise on Invertebrate Paleontology. University of Kansas Press & Geological Society of America, Boulder.