molluscs

Question 1

what are the three main body parts of a mollusc

Answer 1

1) visceral mass
2) foot
3) mantle

Question 2

what is the visceral mass

Answer 2

1/3 main body parts which contains internal organs

Question 3

what is the foot

Answer 3

1/3 main body parts which is a muscular organ on the ventral surface used for locomotion

Question 4

what is the mantle

Answer 4

1/3 of the main body parts which is the body covering the dorsal surface secreting a calcareous shell for protection

Question 5

what is a radula

Answer 5

a membranous belt which carries rows of teeth and slides over the odontophore (cartilage under the radula)

Question 6

outline the movement of blood in molluscs

Answer 6

• oxygened haemolyphy (not blood as lacks pigment) pumped through arteries to stomach and intestine into the foot which need o2 for locomotion

blood then floods organs in an open circulatory system

Question 7

where can convergent evolution be seen in humans and mollusca

Answer 7

in the eye- similar structure but in vertebrates the optic nerve passes through the cells detecting light vs in mollusca it is behinde so they dont have a blind spot

Question 8

what are the different classes of mollusca phylum

Answer 8

• aplacophora
• polyplacophora
• monoplacophora
  -gastropoda
• bivalvia
• scaphopoda
• cephalopoda

Question 9

outline characteristics of the class aplacophora (without a plate)

Answer 9

• lacks a shell, mantle and foot
• mantle covered in calcareous scales

Question 10

outline characteristics of the class polyplacophora (many plates)

Answer 10

• shell composed of 8 overlapping plates
• common on rocky shores

Question 11

outline characteristics of the class monoplacophora (single plate)

Answer 11

• all marine
• live at great depths
• one symmetrical shield shaped shell

Question 12

outline the class bivalvia

Answer 12

• two valves
• clams, oysters, mussels etc
• most microphagous feeders
• laterally compressed body enclosed with 2 valves
• muscles have a catch fibre mechanism

Question 13

outline the class scaphopoda

Answer 13

• tusk shells
• burrowing marine molluscs
• shell is tubed shape with two open ends
• gas exchange through mantle surface
• feed on microscopic intersitial organisms

Question 14

outline the class cephaloaopoda

Answer 14

includes squids, cuttle fish and octopods
- food divided into tentacles or arms anteriorally around the mouth
swim by jet propulsion

Question 15

what is the subclass of cephaloapods - nautiloidea

Answer 15

possess an external coiled shell
no suckers or arms
many tentacles

Question 16

what is the subclass of cephalopods - coleoidea

Answer 16

8 arms
2 tentacles
shell with septa is reduced or lost
e.g. cuttle fish
short body