Dip below the ocean's surface and you are soon confronted by forms of life that could not seem more foreign to our own: sea sponges, soft corals, and serpulid worms, whose rooted bodies, intricate geometry, and flower-like appendages are more reminiscent of plant life or even architecture than anything recognizably animal. Yet these creatures are our cousins. As fellow members of the animal kingdom--the Metazoa--they can teach us much about the evolutionary origins of not only our bodies, but also our minds.