beauty of this group resides in that design. Later in this lesson, learn how symmetry takes
advantage of the animal’s habitat.
Figure 12.10: A starfish, showing the radial symmetry, characteristic of the echinoderms. ( 8 )
Figure 12.11: Another echinoderm. a sea urchin, showing its calcareous spines. ( 33 )The other things that stand out, quite literally, are the calcareous (containing calcium car-
bonate) spines of the sea urchin. If you’ve gone snorkeling or walked on a sandy beach you’ve
learned to most likely watch out for those sharp spines. Think about how this adaptation
might benefit the sea urchin in terms of predation and colonization by other organisms. Can
you think of another use of these structures?