Chapter 27, Problem 7STP

Summary Introduction

Introduction:

Chordates have hollow nerve cords. The phylum chordates have vertebrates like fishes, amphibians, reptiles, mammals. There is a great diversity in vertebrates of fishes, amphibians, etc.

Answer to Problem 7STP

Correct answer:

The correct answer is option (A) 1.

Explanation of Solution

Explanation/justification for the correct answer:

Option (A) 1. The indicated arrow number 2 in the image shows the dorsal tubular nerve cord. The dorsal tubular nerve chord is one of the distinctive features of the phylum chordates. It develops into the central nervous system. It contains a bundle of nerves that is protected by fluids. So, this is the correct answer.

Explanation for incorrect answer:

Option (B) 3. The number 3 in the image indicates muscle blocks. The muscle blocks are the “w” or “v” shaped muscle fibers in the chordates but it does not contain a bundle of nerves that is protected by fluids. So, this is an incorrect option.

Option (C) 5. The number 5 in the image indicates the ancestral thyroid gland. The ancestral thyroid gland in chordates regulates growth, metabolism, and development. It does not contain a bundle of nerves that are protected by fluids. So, this is an incorrect option.

Option (D) 6. The number 6 in the image indicates the postanal tail. It is seen in chordates at the end part and is used for locomotion. However, it does not consist of a bundle of nerves. So, this is an incorrect answer.