Echinoderms (Phylum Echinodermata) are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. Aside from the problematic Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period The phylum contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates; they're also the largest phylum that's no freshwater or terrestrial representatives. The… (More on Echinodermata)