Conway Morris, S., 1993: The fossil record and early evolution of the Metazoa. --Nature, vol. 361, 21 January, pp. 219-225
The Tree of Life site has an excellent cladogram and discussion of the relationships of Echinodermata, both living and extinct. It differs in a number of respects from our arrangement. The Berkeley UCMP page has yet another arrangement -- a bit more like our own but probably somewhat out of date. Mikko Haaramo's cladogram -- from which ours is derived -- may be found at Echinodermata. For those determined Linneans out there, the California Academy of Sciences maintains a Linnean scheme at Classification of the Extant Echinodermata. Finally, Tom Holtz has a good discussion of the issues in his course notes at GEOL 331 Lectures 32-33- Echinodermata. ATW050801.