Lecture 13: Mollusca

Question 1

The radula

Answer 1

rasping organ that reduces prey to small fragments passed into pharynx

Question 2

The foot

Answer 2

attached animal to substrate

Question 3

The mantle

Answer 3

secretes a shell to protect mollusc

Question 4

Three layers of shell

Answer 4

1. Periostracum (outermost)
2. Prismatic (middle)
3. Nacreous (innermost)

Question 5

The shell

Answer 5

elongated cone that spirals into a central axis so it is easier to carry

Question 6

The nervous system

Answer 6

• consists of ganglia and nerve cords
  cerebral ganglia: located above oesophagus
  pedal ganglia: beneath oesophagus
  pleural ganglia: behind and below ganglia

Question 7

Glial Cells

Answer 7

• electrical insulation of nerve cells

- provide nutrients, O2, maintain extracellular environment, fight infections etc.

Question 8

Resting

Answer 8

• negative inside neuron

- K and Na closed

Question 9

Depolarization

Answer 9

• Na channels open

Question 10

Hyperpolarization

Answer 10

• Na channels close, K channels open

Question 11

Torsion

Answer 11

• twisting of visceral mass unit until mantle cavity, gills, anus, gonopore and nephridiopore are anterior above the head

Question 12

Metamorphosis of Mollusc

Answer 12

• veiger lives for a few hours to a few weeks in plankton

- sinks to bottom and begins to crawl or attach

Question 13

Conus

Answer 13

• modification of radula, used for protection (launch harpoon to poison prey)

Question 14

Naudibranches

Answer 14

• don’t go through torsion

- very poisonous

Question 15

Pterotrachea

Answer 15

• have modified foot into ventral swimming fin

Question 16

Corolla

Answer 16

• foot adapted into two wing like lobes that propel the animal through water

Question 17

Pulmonate gastropods

Answer 17

• snails/slugs

Question 18

Scaphopoda

Answer 18

• slightly curved tubular shell

- lies burrowed in the mud

Question 19

Cephalopoda

Answer 19

squids and octopuses

• foot fused into tentacles
• shell reduced or absent

Question 20

Nautilus

Answer 20

• has coiled chambered shell
• many tentacles without suckers
• locomotion by jet propulsion using funnel

Question 21

Polyplacophora

Answer 21

• creeping scrapers
• lack eyes and tentacles
• concealed by overgrowth of mantle

Question 22

Monoplacophora

Answer 22

• has external gills

- has foot retractor muscles and nerve branches

Question 23

Aplacophora

Answer 23

• no head, mantle, foot or shell

- body covered with calcareous spicules