We saw a very nifty critter crawling by the lens of the underwater camera at Orca-Live. Spikes on top, tube-feet on the bottom. Plainly orange-ish. Looked quite a lot like the picture of a California sea cucumber which we found in Brock Filer's Biognomen pages.
He points to a couple of other evolutionary trees, the Tree of Life Web Project, and the Phylogeny of Life pages at the University of California Museum of Paleontology site. But for starting with a critter and working backward to see where it fits in, we like the Biognomen pages. Mister Spikes-and-Tube-Feet comes clearly labelled as Animalia- Echinodermata- Hemichordata- Rhombifera- Crinoidea- Ophiocistioidea- Holothuroidea-Parastichopus californicus
(Just in case you like that much specificity... )