Chapter 27, Problem 1TYU

Summary Introduction

Introduction:

Clade refers to a grouping that includes an ancestor and all of its descendents.

Answer to Problem 1TYU

Correct answer:

The bilaterian is the clade that contains the greatest number of animal species. Therefore, option (B) is correct.

Explanation of Solution

Reason for the correct statement:

The division of body into two equal halves and presence of three germ layers are the shared derived characters that define the clade “Bilateria”. This clade comprises the most of the animal phyla and it members.

Option (B) is given as “the bilaterians”.

As,” the bilaterian is the clade that contains the greatest number of animal species”, it is the right answer.

Hence, option (B) is correct.

Reason for the incorrect statements:

Option (A) is given as “the vertebrates”.

The vertebrates are those animals that are characterized by the presence of notochord, pharyngeal gill slits, dorsal nerve cord and post-anal tail. They do not comprise the greatest number of animal species. So, it is a wrong answer.

Option (C) is given as “the deuterostomes”.

The deuterostomes are those animals that develop anus first and mouth later and they do not comprise the greatest number of animal species. So, it is a wrong answer.

Option (D) is given as “the insects”.

The insects are hexapod animals with two pair of wings, exoskeleton and antennae, and they do not comprise the greatest number of animal species. So, it is a wrong answer.

Hence, options (A), (C), and (D) are incorrect.

Conclusion

The bilaterians is the clade that contains the greatest number of animal species.