Chapter 27, Problem 20A

Summary Introduction

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.

Answer to Problem 20A

Correct answer:

The correct answer is option (D) locomotion

Explanation of Solution

Explanation/justification for the correct answer:

Option (D) locomotion. A postanal tail is a structure that is mainly used for mobility, behind the digestive system and anus. The postanal tail stretches beyond the anus, in most chordates. So, the correct answer is option (D).

Explanation for incorrect answer:

Option (A) circulation. Chordates used postanal tail for mobility. So, this is an incorrect answer.

Option (B) digestion. In nonchordate, tails have internal portions of the digestive tract, and the anus is found at the end of the body. The postal tail is used to carry locomotives. So, this is an incorrect answer.

Option (C) flexibility. The notochord flexibility causes the body to stretch, instead of shorten, during muscle segment contractions. So, this is an incorrect answer.