Animal - Mollusca

Question 1

This characteristic is NOT a definitive feature of a mollusc:

Answer 1

A shell

Question 2

What are the 5 defining features of the H.A.M.?

Answer 2

1) Cephalization
2) Visceral mass
3) Mantle
4) Mantle cavity
5) Radula

Question 3

What are the 4 classes of molluscs?

Answer 3

• Polyplacophora
• Gastropoda
• Bivalvia
• Cephalopoda

Question 4

Polyplacophora

Answer 4

Chitons

Question 5

Gastropoda

Answer 5

Snails and Slugs

Question 6

Bivalvia

Answer 6

Oysters, clams, mussels, scallops, etc.

Question 7

Cephalopoda

Answer 7

Squids and Octopi

Question 8

Function of the radula:

Answer 8

Long flexible strip with teeth used for feeding. Scrapes against the tops of food.

Question 9

What does Cephalization mean?:

Answer 9

It is a distinct separation of the head-foot region. Clear distinction of the head.

Question 10

What is the visceral mass?

Answer 10

The visceral mass holds all the internal organs (guts).

Question 11

Mantle cavity:

Answer 11

A space at the posterior of the animal that typically contains the gills and acts as a water space.

Question 12

Describe the class chitons fit into and the characterization of them.

Answer 12

Chitons are within the class polyplacophora.
(1) They are a single shelled animal with 8 part valve (1 shell, 8 parts).

(2) They are dorsoventrally flattened, meaning extending from the back to the belly (upper and lower parts), the chiton is flat.

(3) They have ONE large central foot, making their movement imperceptibly slow and

(4) They are not cephalized.

Question 13

Gastropodas and Polyplacophora are both this type of feeder:

Answer 13

Grazers - they use their radula to scrape the top off their food (ex. the bamboo).

Question 14

What type of shell shape is the most favorable and why?

Answer 14

Asymmetrical spiral shell with a (approx. 45 degree) tilt.

It creates a good balance for weight and it is compact which increases the strength of the shell.

Question 15

What are the other two shell types and the advantages and/or disadvantages to both?:

Answer 15

Asymmetrical spiral (no tilt) - All the weight is off to one side of the body creating an imbalance on the animal. It is compact and strong but not favored and not a shell found in many gastropods.

Planospiral - simple spiral without tilt. Not very strong.

Question 16

What is a class specific development that ONLY the gastropods exhibit?

Can you describe what the advantages are of this process/hypotheses?

Answer 16

During the developmental stages, a gastropod will undergo torsion where their Mantle cavity will shift from the posterior to the anterior. This is a 180 degree rotation.

The hypotheses for the cause of this process is that it creates better air quality for the class and is better for defense. With the mantle cavity located at the anterior end of gastropods the air quality is better because the gills are no longer near the rear side and the when it comes time to retract into the Mantle cavity, the head will retract first instead of the foot due to having the cavity at the front.

Question 17

Why do gastropods spiral their shells?

Answer 17

It increases their size and it also increases the strength of their shells. The more compact it is, the stronger the shell?