Molluscs

Molluscs

Molluscs are aquatic or terrestrial invertebrates with bilateral symmetry that, in most cases, have a protective shell.

Molluscs have the following body parts

• A head which contains sense organs

• A visceral mass. Where internal organs are found. It is covered with a sheet of tissue called the mantle

• A muscular foot which is different on each group and it is used for moving, digging or catching prey.

General characteristics

• ➜ Aquatic molluscs breathe through gills; terrestrial  molluscs through lungs.

   ➜ They have a more or less developed nervous system

   ➜  They can be herbivores or carnivores. Some feed by  filtration.

   ➜  They  reproduce sexually and most of them are  hermaphrodites. 

The main types of molluscs

Classification

Open Ended

Describe the body parts of a mollusc.

Gastropods

• Most gastropods have a single spiral- shaped shell.

• In their mouth they have a scraper organ, called a radula, which they usse to feed themselves.

Multiple Choice

What is the function of the radula in a snail?

• They use it to feed themselves

• They breathe with it

• It produces the shell

Bivalves

• Most bivalves have a shell formed of two  hinged valves

• Their foot, in the shape of a wedge, is used to move and dig.

Open Ended

What is the function of the foot in bivalves?

Cephalopods

• Most cephalopods have an internal  shell called gladius.

• They have a well-developed eyes and a set of tentacles around the mouth.

• They have a mandible called a beak.

Open Ended

1. What is the function of the shell of a clam?

2. Describe the foot of a mussel and of a squid.

3. What types of molluscs have a well-defined head?