Molluscs

Question 1

The molluscs are hugely diverse, second only to the…?

Answer 1

Arthropods

Question 2

They have colonised a huge range of habitats. Give examples.

Answer 2

Marine, freshwater, deep ocean, thermal vents, terrestrial etc.

Question 3

Are molluscs bilaterian?

Answer 3

Yes.

Question 4

Are molluscs proto or deuterostomes?

Answer 4

Protostomes: they fall into the lophotrochozoa

Question 5

What kind of cleavage do protostomes have?

Answer 5

Spiral: cells turn 45 degrees counter-clockwise to each other during division

Question 6

What kind of fertilisation do most molluscs have?

Answer 6

External, although there are exceptions.

Question 7

Lophotrochozoans have characteristic larvae. What are they?

Answer 7

Trochophore larvae: they have ciliated organs (that they are named after) for movement. They feed on plankton.

Question 8

After the trochophore stage is the veliger stage. What is a veliger larvae?

Answer 8

More developed: has extended tissue, lots of cilia, sensory organs and a protocomb.

Question 9

What is a protocomb?

Answer 9

A tiny shell.

Question 10

Terrestrial molluscs skip some of the larval stages of marine species. Why?

Answer 10

They need to develop quicker.

Question 11

Describe the nervous system of a mollusc.

Answer 11

Cephalisation: they have a circumcentric nerve ring and 2 longitudinal nerve chords.

Question 12

How do most molluscs move?

Answer 12

Via a ventral ‘foot’

Question 13

Where are all the major organs found in molluscs?

Answer 13

The DCVM or ‘dorsal central visceral mass’.

Question 14

The DCVM is covered by the a) mantle and b) mantle cavity. What do these structures do?

Answer 14

a) A thick dorsal cuticle that secretes the calcareous shell

b) Encloses water and thus the respiratory chamber, as well as the kidneys, gonads and single opening (mouth/anus)

Question 15

Are molluscs coelomates?

Answer 15

Yes.

Question 16

What is the hemocoel?

Answer 16

The principle blood cavity.

Question 17

What is the pigment in molluscan blood?

Answer 17

Hemocynin.

Question 18

The immunity of molluscs is adaptive. True or false?

Answer 18

False: however it is very sophisticated.

Question 19

What is a radula?

Answer 19

‘A ribbon of chitinous, recurve teeth supported by the odontophore’.

Basically a tongue covered in teeth.

Question 20

Do all molluscs possess radulae?

Answer 20

Yes, however it is modified depending on food source etc.

Question 21

Do we have a good fossil record of molluscs?

Answer 21

Yes: their hard shells preserve well. Plus their radulae produce many trace fossils.

Question 22

There are 7 major classes of mollusc. What are they?

Answer 22

1. Bivalves
2. Monoplacophorans
3. Gastropods
4. Cephalopods
5. Scaphopods
6. Aplacophorans
7. Polyplacophorans

Question 23

Briefly describe a bivalve.

Answer 23

Have 2 ‘half shells’ that can be used for locomotion. These shells are opened/closed by powerful muscles/ligaments.

Question 24

How do bivalves feed?

Answer 24

The mantle cavity contains very large gills that trap food suspended in inhalant water.

Question 25

How many siphons do bivalves have?

Answer 25

2: these are to circulate water.

Question 26

Bivalves can be freshwater or marine. How do they bury into the sediment?

Answer 26

With a large foot.

Question 27

What is unique about bivalves, what do they lack that other molluscs have?

Answer 27

No cephalisation, jaws or radulae.

Question 28

Which is the most primitive mollusc group and when do they originate from?

Answer 28

The monoplacophorans originate from the Cambrian.

Question 29

Briefly describe a monoplacophoran.

Answer 29

A single shell with 5-6 pairs of gills. They are deep-sea dwelling detritivores. They have small tentacles but look like limpets.

Question 30

Which is the most successful/diversified mollusc group?

Answer 30

The gastropods.

Question 31

What kind of niches have gastropods exploited?

Answer 31

All the feeding styles: carnivores, detritivores and suspension feeders. A range of habitats: deep ocean, desert, freshwater, montane, forests etc.

Question 32

How do gastropods reproduce?

Answer 32

They are either hermaphroditic but DO NOT SELF-FERTILISE or can be dioecious.

Question 33

What differs about the development of aquatic and terrestrial species?

Answer 33

Terrestrial species have direct development and skip out the larval stages of the aquatic species.

Question 34

A central structure of the gastropod shell is the columella. What is that?

Answer 34

A central, calcareous axis.

Question 35

The body of gastropods displays torsion due to their coiled shells. True or false?

Answer 35

True.

Question 36

Describe how torsion occurs in gastropods.

Answer 36

There is a 90 degree contraction on one ide of the body - this happens rapidly. The other side is slow to twist, creating disproportionate growth. This flips the nervous system of the mollusc.

Question 37

How is body torsion an adaptive advantage for gastropods?

Answer 37

They can retract the body into the shell more quickly when threatened.

Question 38

The single locomotive foot is covered by what? What does it do?

Answer 38

The operculum: a 'door' that closes the shell upon retraction of the body.

Question 39

Briefly describe a scaphopod.

Answer 39

A marine burrower with its head own in the sediment and captacula (tentacles) sticking up. They have no gills but many cilia.

Question 40

What is characteristic about an aplacophoran?

Answer 40

They have no shells but many spicules. They are worm-like with a reduced foot.

Question 41

The a) solenogastres and b) caudofoveata are both species of aplacophoran. What are their feeding strategies?

Answer 41

a) Carnivores b) Detritivores All species of aplacophoran are marine.

Question 42

How many shells does a polyplacophoran have?

Answer 42

8.

Question 43

What is another name for a polyplacophoran?

Answer 43

A chiton.

Question 44

Describe a polyplacophoran.

Answer 44

A v. strong foot as they live in intertidal zones. Their shells are v. smooth due to wave action. They feed on encrusting organisms like barnacles.