Polyplacophora

Question 1

What is the dorsal view of chitons dominated by?

Answer 1

8 shell valves and mantle

Question 2

Describe the ventral view of chitons

Answer 2

Head: knob with mouth
Foot: muscular, clings to rocks
Anus
Osphradia (sensory)

Question 3

Explain how the chiton clings to rocks

Answer 3

1. It uses its muscular foot to attach to substrate
2. A chiton can use muscular action to change the pressure inside the pallial cavity, and this creates suction to stick it to the substrate

Question 4

Where are the ctenidia located? How many are there?

Answer 4

In the pallial cavity: the space between the foot and the girdle

There are two, located in the pallial cavities on either side of the chiton.

Question 5

Describe the cross section of a chiton

Answer 5

Question 6

What are the dorsal and ventral sides called?

Answer 6

ventral: cephalopodium
dorsal: visceropallium

Question 7

Describe hemolymph flow through the ctenidia

Answer 7

Question 8

Are the digestive tract and gonad contained in a eucoelomic compartment?

Answer 8

No, it is a hemocoel. It is a space in the in the connective tissue not lined by epithelium, like a true coelomic compartment would be.

Question 9

What does the true coelom form in chitons?

Answer 9

The pericardium- the cavity around the heart.

Question 10

What are the components of the digestive tract

Answer 10

1. Mouth
2. Buccal cavity
3. Radular cartilages
4. Radular sac
5. Stomach with digestive gland
6. Intestine
7. Anus

Question 11

What secretes the radula?

Answer 11

The radular sac

Question 12

What is the radula used for? Is this the ancestral or derived form of this action.

Answer 12

1. Used for feeding-scraping algae off rocks
2. This is the ancestral form

Question 13

Describe how feeding works in chitons

Answer 13

1. Cartilage extruded (is covered w radular ribbon) and presses against rocks
2. Protraction and retraction of radular teeth scrapes it along rock

Question 14

What is the chiton’s nervous system composed of?

Answer 14

1. Circumpharyngeal nerve ring
2. Visceropallial nerve chords
3. Pedal nerve chords (near foot)

Question 15

What are 5 distinct characteristics of chitons and reasons behind them?

Answer 15

1. Minimal cephalization: don’t move rapidly
2. Dorso-ventral flattening: resist wave action
3. Dorsal shell as 8 pieces: shell valves move relative to each other to cling to rocks
4. Mantle assists with adhesion: A chiton can use muscular action to change the pressure inside the pallial cavity, and this creates suction to stick it to the substrate
5. Radula with magnetite caps

Question 16

What extant bivalves have a radula?

What about cephalopods?

Answer 16

None

Some cephalopods have secondarily lost it

Question 17

Describe Chiton reproduction

Answer 17

1. Dioeceous
2. Broadcast spawn
3. External fertilization
4. Ciliated, non-feeding larva