"Echinodermata" an article written by Gregory A. Wray is about the extensive fossil record of the highly-derived clade of Metazoans, their importance in the marine realm, and their adult morphology. It explains all of the clades, which includes; Crinoidea, Ophiuroidea, Asteroidea, Echinoidea, and Holothuroidea.  The article then continues with a description of characteristics and concludes with a discussion of phylogenetic relationships. 

http://tolweb.org/Echinodermata

"Introduction to the Echinodermata", an article written by the Regents of the University of California discusses the largest phylum, Echinodermata. The article talks about Starfish, brittle stars, sea cucumbers, and sea urchins. 

http://www.ucmp.berkeley.edu/echinodermata/echinodermata.html

I thought the first article was much more interesting and had more information compared to the second one.