AD Molluscs

Question 1

Describe a mollusc’s shell

Answer 1

Early molluscs had a proteinaceous and chitinous cuticle
Progressively reinforced with calcium
Modern shells consist of crystals of calcite and argonite deposited within a framework of layers of protein (conchiolin)
Muscles pull the shell down to protect the head and foot when needed
Often conical or helically coiled

Question 2

The contraction of which 2 muscles protracts the odontophore and radular ribbon through the mouth?

Answer 2

Radular protractor muscle

Odontophore protractor muscle

Question 3

What part of a mollusc’s body is generally used to identify a mollusc remains from the guts of predators

Answer 3

Radula teeth

Question 4

Describe an Aplacophora

Answer 4

No shell
Calcerous spines
Worm like
<300mm
Headless and no proper foot
Live in marine sediments
Most have a radula but no excretory organs
Hermaphrodites

Question 5

Describe a Polyplacophora (chitons)

Answer 5

8 overlapping plates
Can roll into a ball
Girdle of spiny cuticle
<400mm
Powerful foot
Marine eg shores
Kidneys but head poorly defined
Radula
6-88 pairs of ctenidia

Question 6

What are ctenidia?

Answer 6

Gills

Question 7

Describe a Monoplacophora

Answer 7

Conical shell
<30mm
Weak foot
Marine eg deep trenches
Head poorly defined and no eyes/tentacles
6 pairs of kidneys
Radula
Detrital feeders
Mantle cavity around foot
3-6 pairs of ctenidia

Question 8

Describe a Scaphopoda (tusk shells)

Answer 8

Cylindrical shell
<150mm
Separate sexes
Burrowing foot
Marine sediments
Head, no eyes but a radula
Mantle cavity through body
No ctenidia
Ciliated contractile tentacles

Question 9

Describe a bivalvia

Answer 9

Pair of shells
<1m
Separate sexes
Some use foot to burrow or others cemented to substrate (byssus)
Head has no eyes, no tentacles, no radula
May be tentacles around eyes or mantle
Ctenidia highly modified

Question 10

Describe a gastropoda

Answer 10

Snail
Largest and most diverse group
Torsion
Single coiled shell with operculum (generally)
Well developed head with eyes, radula and sensory tentacles
Well developed crawling foot
May be gonochoristic or hermaphrodites

Question 11

Describe gastropoda torsion

Answer 11

Rotation of visceral hump through 180°
Mantle cavity now faces forward
Anus discharges into mantle cavity over the head
Having the mantle cavity at the front allows the well-developed head to be withdrawn into the shell
Chemoreceptors within the mantle cavity can now monitor the water ahead, rather than behind

Question 12

Describe Gastropoda - Superorder Opisthobranchia

Answer 12

Sea-slugs, sea-hares
Secondary gills or papillate body surface
Up to four pairs of tentacles
Most are carnivores
Includes planctonic mucus net feeders (pteropods) with ciliated wings

Question 13

Describe Gastropoda - Superorder Pulmonata

Answer 13

Mainly terrestrial or freshwater
Mantle cavity evolved into air-breathing lung with pneumostome
Shell thinned or lost
Most are grazers of plants or fungi, some carnivores

Question 14

Describe Gastropoda - Superorder Pulmonata Anatomy

Answer 14

Mantle cavity, heart, kidney, salivary gland, digestive gland, rectum, reproductive system, brain, foot

Question 15

What is a Cephalopod?

Answer 15

Squid, octopus, cuttlefish

Question 16

What is a Cephalopod’s body plan?

Answer 16

Mantle cavity opens forwards
Rapid, directed movement effected by expelling water through manoeuvrable funnel
Prey caught with arms/tentacles, chewed up by beak then radula
Gonochoristic and most are short lived (1-2 years)
90° body tilt then elongation

Question 17

Describe a Cephalopod - Nautiloidae

Answer 17

Body is in external shell
Last segment is inhabited
Siphuncule controls gas/water balance in other chambers to control buoyancy
Poor swimmers – water expelled by funnel muscle
80-90 suckerless tentacles
Two pairs of ctenidia and kidneys
Nervous system and eyes simple

Question 18

Describe the anatomy of Cephalopod - Celeoidae - Sepiida, Cuttlefish

Answer 18

Stomach, digestive gland, shell, salivary gland, brain, buccal mass, funnel, gonad, ink sac, fin, gill

Question 19

Describe the anatomy of Cephalopod - Celeoidae - Teuthida, Squid

Answer 19

Stomach, digestive gland, brain, ‘pen’, buccal mass, ink sac, funnel, crop, mantle, siphon, parrot-like beak and mouth, 8 arms and 2 rows of suckers, 2 long feeding tentacles

Question 20

Describe the anatomy of Cephalopod - Celeoidae - Octapoda, Octopus

Answer 20

Brain, digestive gland, buccal mass, crop, kidney, funnel, branchial heart (3?), salivary gland

Question 21

Describe an Octopus’ brain

Answer 21

Large optic lobes

Vertical lobe, optic stalk, brachial lobe,

Question 22

What do the bivalve gills demonstrate?

Answer 22

How organs that originally evolved for one function can be further adapted for use in totally different ways
Bivalve mollusks breathe through their gills. As filter feeders, bivalves gather food through their gills.

Question 23

What are the classical features of the Coleoidea?

Answer 23

the large brain, the advanced eye structure, powerful jet propulsion, control over their own body patters and colours, multifunctional tentacles and a vascular system with veins and arteries