Echinoderms (Phylum Echinodermata) are a phylum of marine animals (including sea stars) found at all ocean depths. Aside from the problematic Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period, and contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates; they're the largest phylum without freshwater or terrestrial representatives. The word derives from the Greek εχι�… (More on Echinoderm)