Graphic used with permission. Daniel D. Brown, LaughingMantis.com.   Echinoderms are one of the most highly derived groups of animals with many species as significant components of several marine communities. They’re classified by three fundamental shared characteristics: 1) pentaradial symmetry, 2) skeleton made of three-dimensional calcitic elements, and 3) the presence of a water . . . → Read More: Veins of Water: The Evolution of the Echinoderm Water-Vascular System