Chapter 34, Problem 42A

Summary Introduction

To draw:

Well labelled diagram of organisms belonging to the three classes of mollusks.

Introduction:

Mollusks belong to the Mollusca phylum which are characterized by the presence of mantle, muscular foot, soft internal body, two openings in the digestive tract, coelom, and bilateral symmetry. Some mollusks also have shells formed by the calcium carbonate secreted by mantle.

Explanation of Solution

Mollusks are further divided into three classes. The description of each class along with a diagram of an organism from that class is as follows:

1) Gastropods: These organisms are characterized by the presence of a shell round their body, a muscular foot used for locomotion, and a head with eyes, 1-2 tentacle pairs, and bunch of ganglion. Snails come under this category. A well labelled diagram of a snail is shown below:

  

2) Bivalves: These organisms are characterized by the presence of valves or two shells. The valves protect the inner soft body of the organism. The organism can open the shell to feedand move and close it when it senses any threat. Oysters belong to this class. A well labelled diagram of an oyster is shown below:

  

3) Cephalopods: These organisms are characterized by the presence of merged foot and head. They also have rings of tentacles or arms around the head. Squids belong to this class. A well labelled diagram of a squid is shown below: