Chapter 27, Problem 17A

Summary Introduction

To determine: The structure located just below the nerve cord in chordates that enables invertebrate chordates to swim by moving their tails back and forth.

Introduction: Chordates are species belonging to the phylum Chordata that at some stage during their development have four distinctive characteristics-a dorsal tubular nerve cord, pharyngeal pouches, a notochord and a postanal tail.

Explanation of Solution

The notochord is an elastic, rod-like structure, extending the body length. It lies just below the nerve cord of the dorsal tubular. The notochord is replaced by bone or cartilage in most vertebrate animals. The notochord persists in the chordate of vertebrate individuals. An animal having a notochord can create side-to-side body and tail movements, making fish-like swimming possible the first time in the history of evolution.

Conclusion

Thus, it concludes that the notochord is the device found in chordates just below the nerve cord allowing invertebrate chordates to move by flipping their tails back and forth.