Chapter 28, Problem 4A

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 found.

Answer to Problem 4A

Correct answer:

The correct answer is option (B) lateral line system.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) lateral line system. The given structure labelled A is called lateral line system. The lateral line system are receptors for the sense of smell in fishes. It enables fishes to detect movement in the water and also help to keep them upright and balanced. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) ctenoid scales. These are a type of scales found in fishes. There are four types of fish scales. Ctenoid scales are thin and flexible. So, this is an incorrect option.

Option (C) neural crest. As the nerve cord develops during embryonic development in vertebrates, there is another phase called neural crest develops. The neural crest is a group of cells that develop in vertebrates from the nerve cord. Although the cell group is small, it is significant in the development of vertebrates because many important vertebrates develop from the neural crest. So, this is an incorrect answer.

Option (D) operculum. Operculum is a movable membrane that covers and protects the gills. It also helps to pump water into the mouth and gills. So, this is an incorrect answer.