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2nd Year: Animal Biodiversity > Molluscs > Flashcards

Molluscs Flashcards

1
Q

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

A

Arthropods

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2
Q

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

A

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

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3
Q

Are molluscs bilaterian?

A

Yes.

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4
Q

Are molluscs proto or deuterostomes?

A

Protostomes: they fall into the lophotrochozoa

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5
Q

What kind of cleavage do protostomes have?

A

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

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6
Q

What kind of fertilisation do most molluscs have?

A

External, although there are exceptions.

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7
Q

Lophotrochozoans have characteristic larvae. What are they?

A

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

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8
Q

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

A

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

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9
Q

What is a protocomb?

A

A tiny shell.

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10
Q

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

A

They need to develop quicker.

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11
Q

Describe the nervous system of a mollusc.

A

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

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12
Q

How do most molluscs move?

A

Via a ventral ‘foot’

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13
Q

Where are all the major organs found in molluscs?

A

The DCVM or ‘dorsal central visceral mass’.

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14
Q

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

A

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)

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15
Q

Are molluscs coelomates?

A

Yes.

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16
Q

What is the hemocoel?

A

The principle blood cavity.

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17
Q

What is the pigment in molluscan blood?

A

Hemocynin.

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18
Q

The immunity of molluscs is adaptive. True or false?

A

False: however it is very sophisticated.

19
Q

What is a radula?

A

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

Basically a tongue covered in teeth.

20
Q

Do all molluscs possess radulae?

A

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

21
Q

Do we have a good fossil record of molluscs?

A

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

22
Q

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

A
  1. Bivalves
  2. Monoplacophorans
  3. Gastropods
  4. Cephalopods
  5. Scaphopods
  6. Aplacophorans
  7. Polyplacophorans
23
Q

Briefly describe a bivalve.

A

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

24
Q

How do bivalves feed?

A

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

25
Q

How many siphons do bivalves have?

A

2: these are to circulate water.

26
Q

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

A

With a large foot.

27
Q

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

A

No cephalisation, jaws or radulae.

28
Q

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

A

The monoplacophorans originate from the Cambrian.

29
Q

Briefly describe a monoplacophoran.

A

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

30
Q

Which is the most successful/diversified mollusc group?

A

The gastropods.

31
Q

What kind of niches have gastropods exploited?

A

All the feeding styles: carnivores, detritivores and suspension feeders.

A range of habitats: deep ocean, desert, freshwater, montane, forests etc.

32
Q

How do gastropods reproduce?

A

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

33
Q

What differs about the development of aquatic and terrestrial species?

A

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

34
Q

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

A

A central, calcareous axis.

35
Q

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

A

True.

36
Q

Describe how torsion occurs in gastropods.

A

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.

37
Q

How is body torsion an adaptive advantage for gastropods?

A

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

38
Q

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

A

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

39
Q

Briefly describe a scaphopod.

A

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

40
Q

What is characteristic about an aplacophoran?

A

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

41
Q

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

A

a) Carnivores
b) Detritivores

All species of aplacophoran are marine.

42
Q

How many shells does a polyplacophoran have?

A

8.

43
Q

What is another name for a polyplacophoran?

A

A chiton.

44
Q

Describe a polyplacophoran.

A

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.

2nd Year: Animal Biodiversity (16 decks)

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