Questions and Answers about BIOLOGY

by Ken Miller and Joe Levine


QUESTION: What is the difference between radical and bilaterall symmetry? (from r4r22 in Ohio)

Well, Ohio, ... I can't help you with "radical" symmetry, although I'm sure it's really "far out" (as we used to say in the 60s!).

"Radial" symmetry is another matter, however! Radial and bilateral symmetry are very well-explained on page 662 of the Dragonfly book:

As Figure 26-5 on that page shows, if an animal has radial symmetry, then its body plan is a little bit like that of a bicycle wheel. Any number of planes can be drawn through its center, each dividing the animal into matching halves. Starfish and sand dollars are good examples of animals that show radial symmetry.

Bilateral symmetry best describes our own body plan (as well as that of a lobster). Only a single plane, running the length of the body, can divide the animal into two halves that are mirror images of each other.

Ken Miller (2/14/02)

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(A web site developed by Ken Miller and Joe Levine to provide scientific and educational support for teachers and students using our textbooks)