Evolution

Echinoderms , it has been argued, shared a common ancestor that broke into the two lines , echinodermata/crinoidea etc and the chordates. This split , based upon taxonomic bases is explained in the Treatise on Paleontology. Since echinoderms developed and flourished in the Ordovician (Eo Crinodea developed in the Cambrian , but you are mostly interested in the "Pentacle symmetric ones". ) . Id google up some sites on echinoidea or Pentamerides etc. Fossils are found worldwide and are good Ordovician index fossils , because most of the classes of echinoids start in the Ordovician. The heios started and ended in the early Cambrian, the Edriostrats went from the Cambrian to the Mississippean The others , including sea cucumbers (free livers) lasted into the present and some of these, the holothurians and ananchytes have a lifelong bilateral symmetry.
We use these for environmental indicatorsand paleontologists devote a lot of time in these fossils because the classification is still being argued. (I usually glaze over when these guys get talkinhg about echinoids)

The upper Silurian,mid Devonian,Mississippean.ennsylvanian, Permian and the Creataceous, all had a "crinoid boom or a boomlet" so there are ample species of each of the 4 subclasses of this class. We use these in index fossil means to help correlate the stratigraphy of marine deposits. Im no expert in paleo but Im usually the economic geologist "team leader" (and often the investor). Im n ot up on the evolutionary significance of this entire phylum except that due to the formation preference of the coelum echinos and molluscs shared a common ancestor and the chordata "may" have budded from the echinoderms via a common ancestor .
If your looking for fossils, The best US locales that I know of are in the panhandle of the Appalachian foldbelt of West Virginia and the limestones of Missouri. They ar e found in the Atlas provinces and Caledonian , but Ive only seen those in collections.
Do you have access to The Treatise? Its the multivolume set of paleo and is THE reference. I dont know whether its on the web by subscription but any good University library has more than one set, as its updated periodically

There are some non radially symmetric Cambrian protochordates like Pikeia from the Burgess Shale, that seem to have no Phylletic political attachment. Since the Burgess has some economic value, Ive always been interested in worldwide occurences of this species since it is so localized in its life zone

As far as the importance of echinoderms, I look at fossils more as a tool. To my business , they are more a diagnostic tool that allows me to describe and evaluate a specific geologic horizon. I dont have the training or in depth skills to get into the evolutionary significance of this phylum. If you wish, I can find some references and classical texts on the range and geologic occurences of many of these fossils and localities. Im in the field now but I check in a couple times a day when i take breaks or if Im up late .

Some geological information would be great. I think echoniderms are somehow a key to some of the missing links. Though I am new to this field, their metamorphosis from bilateral to radial symmetry seems uncharacteristic of evolution and natural selection. It almost seems as it would be a temporary downgrade due to some environmental factors. Therefore geoliogical information would prove most helpful. I will check out this Treatise in the meantime.