soft body protected by a hard calcium-containing shell, open circulatory system with hemocoels/sinuses (blood-filled spaces), bilateral symmetry, triploblastic, 3 body zones: head-foot (sensory and motor organs), visceral mass (organs of digestion, excretion, and reproduction), and mantle (specialized tissue that surrounds the visceral mass and secretes the shell), has a radula (movable, tooth-bearing structure, acts like a tongue), most have gills and nephridia, coelomate