Chapter 24, Problem 23A

Summary Introduction

To write:

How some sea anemones seem to possess bilateral symmetry and when bilateral symmetry evolved.

Introduction:

Bilateral symmetry means the animal may be divided into mirror image halves most effective along one plane via the vital axis. All animals with bilateral symmetry develop from 3 embryonic cell layers- the ecotoderm, the endoderm and the mesoderm.

Explanation of Solution

Animals in the phyla Cnidaria and Echinodermata generally show radial symmety, even though many sea anemones and a few corals in the Cnidaria have bilateral symmetry described with the aid of using a single structure, the siphonoglyph. Animals with bilateral symmetry alsohave an anteriorand a posterior end. This body plan isreferred to as cephalization, it's the tendency to concentrate nervous tissue andsensory organs on the anterior end of animals. In addition, animals with bilaterally symmetrical have a dorsal side (top), a ventral side (bottom) and distinct left and right sides. A gene is involved in the evolution of bilateralsymmetry.

Conclusion

It has long been identified that manycnidarians show bilateral symmetry. For example, the sea anemone Nematostellavectensis possesses 2 orthogonal body axes. Thus, some sea anemones appear to own bilateral symmetry and they evolved.