Molluscs

Question 1

What classes make up the molluscs?

Answer 1

Gastropoda, Bivalvia, Scaphopoda, Monoplacopoda, Cephalopoda, Polyplacopoda and Aplacopoda.

Question 2

What material makes up the shells of molluscs?

Answer 2

Calcite crystals and argonite deposited in a protein framework known as conchiolin.

Question 3

What is the mantle?

Answer 3

An organ that secretes the materials to form the shell.

Question 4

What is the radula ribbon and its function?

Answer 4

Acts like a piece of sandpaper, the mollusc equivalent of a tongue. Used for feeding.

Question 5

How do the odontophore and protractor/retractor muscles move the radula?

Answer 5

The odontophore acts as a pulley controlled by the protractor and retractor muscles.

Question 6

What is the odontophore?

Answer 6

Cartilage that is used as a pulley on which the radula sits.

Question 7

What do molluscs use instead of gills?

Answer 7

A ctenidium, a comb/feather shaped organ found in the mantle.

Question 8

What is the heart structure of molluscs?

Answer 8

2 or 3 chambers. The ctenidium sits within the heart.

Question 9

Describe the features of the class aplacophora.

Answer 9

Shell-less with calcareous spines.
Worm like - under 300mm long.
Headless.
Lack a proper foot and excretory organs.
Hermaphrodites.

Question 10

Describe the features of the class polyplacophora (chitons).

Answer 10

Shell of 8 overlapping plates.
Can roll into a ball - resemble woodlice.
Up to 400mm in size.
Powerful foot.
Poorly defined 'head'.

Question 11

Describe the features of the class monoplacophora.

Answer 11

Resemble limpets (convergent evolution).
Up to 30mm in size.
Weak foot.
Poorly defined head (no eyes) + no tentacles.
Mantle cavity around foot.

Question 12

Describe the features of the class scaphopoda (tusk shells).

Answer 12

Cylindrical shells.
Up to 150mm in size.
Separate sexes.
Head lacks eyes but possesses radula.
Mantle cavity goes through body.

Question 13

Describe the features of the class bivalvia.

Answer 13

Pair of shells.
Up to 1m in size.
Separate sexes.
Foot used for borrowing/cementing themselves.
Head lacks eyes, tentacles or radula.

Question 14

What are the 3 forms of gill function in bivalvia?

Answer 14

Protobranch, lamellibranch and septibranch.

Question 15

Describe the features of the class gastropoda.

Answer 15

Single, coiled shell with an operculum (lid).
Highly developed head with radula, eyes and sensory tentacles.
Well-developed crawling foot.

Question 16

What is torsion in gastropods?

Answer 16

The 180° rotation of the visceral mass during development. Leads to the anus being above the head.

Question 17

Describe the features of the class cephalopoda.

Answer 17

90° body tilt then elongation.
Foot has formed arms (8+).
Mantle cavity opens forward.
Hard structures can be internal or external.
Separate sexes.

Question 18

What are the 2 subclasses of cephalopod?

Answer 18

Nautilodea and coleoidea.