How To Study Living Animals


2. THE SNAIL—A TYPE OF MOLLUSCA

To show Another Type of Exoskeleton

Materials.

Specimens of pond snails, edible snails, and “slugs,” and other land snails, and a collection of shells of various types herunterladen.

Definitions.

Gasteropoda,

the name of the class to which the snail belongs.

Spire,

the coiled portion of the snail shell herunterladen.

Aperture,

the opening of the shell.

Lip,

the edge of the shell forming the margin of the aperture.

Whorl,

a single coil of the spire microsoft office kostenlos downloaden vollversion deutsch chip.

Suture,

the depression between the whorls.

Foot,

the flat disk-like structure on which a snail creeps.

Breathing pore,

an opening in the mantle used in respiration.

Lingual ribbon,

the rasp or file like tongue of the snail.

Observations.

1. Why is a snail called a univalve?

2. Identify the head and mouth of the snail. Watch the snail feeding and examine the mouth of the snail with a lens. What do you notice? If your aquarium in which the pond snail is living has a green coating (algæ) on the side, describe its appearance after the snail has been crawling up and down over it. Explain.

3. How many tentacles has a pond snail? a land snail? Where are the eyes located in each case? What movements of the tentacles do you notice? What is their purpose?

4. How does the rate of locomotion of the snail compare with that of the clam? Find out if the snail can creep backwards or on the surface of the water. Does there seem to be any tendency for the snail to go up and down the sides of the aquaria vertically rather than to the right or left?

5. What does a snail do when disturbed? What is gained by this action?

6. Search for pond snail’s eggs on the side of the aquaria. Lift up the bits of cabbage on which the slugs are feeding and search for eggs. Describe what you find in each case, noting the size, appearance, and whether the eggs are laid singly or in masses.

7. Find the breathing pore. Describe its position and appearance.

8. Contrast the various types of shells, and note with care in what respects they differ. Holding the shell with the aperture toward you and the spire pointing up, determine whether each shell has the aperture on the right (right-handed shell) or on the left (left-handed shell). Is the right-handed or the left-handed shell more common?

9. (Optional) By means of some book in the laboratory, determine the scientific name of each of the snails found in the various aquaria in the laboratory.