Hank introduces us to comparative anatomy, which studies the similarities and differences in animal anatomy to support the theory of evolution and the shared ancestry of living things. [8:51]

The five-part symmetry of echinoderms is demonstrated, as the five-armed starfish is morphed into an urchin that is then morphed into a sea cucumber. [1:42]

The squid's body plan has developed for fast action. The shell is reduced to a thin "pen." The mantle wall has elastic fibers that intensify the jet propulsion. Giant nerves allow a fast reflex and three hearts pump oxygen to the gills....

If you draw a line down the middle of the body, both sides are mirror images of each other. With a head and stereo senses leading the way, this body plan is ideal for active hunters. [2:49]

The flatworm's bilateral body plan has a head with a brain and stereo eyes that enable it to actively hunt. Its mouth and pharynx are in the center of its underside. With no circulatory system, the gut distributes food to all parts of...