Aquatic and Land Animal Diversity

Animals in General

Can animals be grouped according to body symmetry?

Yes, animals are often divided into two groups according to their symmetry—the arrangement of body structures in relation to the axis of the body. For example, the bodies of most primitive animals such as jellyfish, sea anemones, and starfish have radial symmetry—a body in the form of a wheel or cylinder, with similar structures arranged as spokes from a central axis. Animals with bilateral symmetry have right and left halves that are mirror images of each other; they also have top (dorsal) and bottom (ventral) portions and a front (anterior) end and back (posterior) end. More sophisticated animals fall into this category, such as flatworms. Some organisms even exhibit both— such as the echinoderms that have bilateral symmetry as larvae and revert to radial symmetry as adults.


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