Chapter 28, Problem 6STP

Summary Introduction

Introduction:

Fishes live in aquatic habitats like lakes, seas, rivers, ponds, etc. Some fishes live in complete darkness at the bottom of the deep ocean whereas others live in the freezing water of the Polar Regions and have special proteins in their blood to keep the blood from freezing. There are about 24,600 species of living fishes are found.

Answer to Problem 6STP

Correct answer:

The correct answer is option (B) 2.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) is 2. The jawless fishes do not have scales, paired fins, or a bony skeleton. They are eel-shaped fishes. They are notochord throughout life. Though they do not develop a vertebral column, they do have gills and many other characteristics of fishes. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) is 1.Invertebrate chordates have lack of a backbone.They are primitive marine organisms. So, this is an incorrect option.

Option (C) is 3. Bony fishes have a skeleton made of bone.They have ctenoid or cycloid scales, an operculum covering the gills and a swim bladder. So, this is an incorrect answer.

Option (D) is 4. All cartilaginous fishes have a skeleton made of cartilage. The skeleton of shark also have is made of cartilage that give the skeleton flexibility and calcium carbonate that gives it strength. So, this is an incorrect answer.