Echinoderms are a moderately successful phylum today with five classes and about 6,000 living species. They are found in all marine environments from the intertidal zone down to the bottom of deep-sea trenches. Because most echinoderms have a stable calcite skeleton made up of many distinctively-shaped plates, spines, stem and arm segments, and other parts, echinoderms have the potential to produce a long and rich fossil record, and we find this to be true. Although our knowledge of this record is far from complete, some past echinoderm faunas may have approached present-day echinoderm communities in number of coexisting genera and species. Also, many classes of echinoderms are known only from the fossil record, and as many as 12–13 classes may have occurred together at some times in the past. Although they have a wide ecologic range today, most fossil echinoderms are found in rocks representing shallow-water, subtidal, marine environments, either past continental shelves or epicontinental seas.