Feeding and Locomotion in Molluscs

Question 1

What feeding method does the generalised mollusc use?

Answer 1

Browser/grazer - e.g. common limpet scraping algae off rocks

Question 2

What molluscs do not have a radula?

Answer 2

Solenogastres and bivalves

Question 3

What feeding methods are seen in molluscs?

Answer 3

• Herbivores
• Carnivores
• Suspension
• Deposit
• Parasites

Question 4

Explain the radula.

Answer 4

The radula is a chitinous ribbon used for rasping food particles, cutting, or drilling holes in prey.

It is covered with numerous small teeth made of chitin. The arrangement/number of teeth differs between species and feeding style.

A flexible mass made of cartilage supports it, called the odontophore.

The radula is controlled by a series of muscles.

It is constantly replaced to maintain feeding effectiveness.

In some species, teeth are tipped with iron oxide, calcium or silica to increase durability and enhance feeding ability.

Question 5

What are the radular teeth tipped with in some species?

Answer 5

Iron oxide, calcium or silica

Question 6

Which gastropods are herbivorous?

Answer 6

Majority of pulmonates - slugs and snails
Some marine and freshwater prosobranchs
Some opisthobranchs - sea slugs, sea hares

Question 7

What is the radula of herbivorous gastropods designed for and what does it look like?

Answer 7

To scrape and rasp food from plants or hard substrate
Lots of rows of many small teeth

Question 8

Give an example of a herbivorous gastropod and describe its feeding method.

Answer 8

Opisthobranch - green sea slug (Elysia chlortica)

• Feeds on seaweeds/algae (macrophagous)
• Employs kleptoplasty - ingests plant material and chloroplasts
• Cells in digestive system phagocytose the chloroplasts
• Also continue to gain energy through photosynthesis at the same time

Question 9

What is kleptoplasty?

Answer 9

Kleptoplasty involves the ingestion and retention of intact chloroplasts from ingested algae.

Question 10

What gastropods are carnivorous?

Answer 10

Most common in marine prosobranchs and opisthobranchs, very few pulmonates

Question 11

What are the adaptations of the radula to a carnivorous diet in gastropods?

Answer 11

Fewer, larger teeth modified to cut and tear rather than rasp
Radula contained within an extendable proboscis that can be inserted into prey
Diversity of feeding methods including acidic secretions, toxins or smothering

Question 12

Give an example of a venomous carnivorous gastropod and explain its feeding mechanism.

Answer 12

Cone snail
Use a modified radular tooth which can be extended using the proboscis to deliver venom to predators

Question 13

Give another example of a carnivorous gastropod.

Answer 13

Dog whelk

Question 14

What ae the 3 major morphological groups of bivalves?

Answer 14

Protobranchs
Lamellibranchs
Septibranchs

Question 15

What is the only group of molluscs where no species have a radula?

Answer 15

Bivalves

Question 16

What is the feeding mechanism of bivalves?

Answer 16

Use gills or other organs to obtain food
Most are suspension feeders (lamellibranchs) but some are deposit feeders (protobranchs)

Question 17

Explain the deposit feeding mechanism of protobranchs.

Answer 17

Extendable palp proboscis used as a sense organ
Palps with mucous secretions used in food collection
Particles are passed towards the labial palps for further sorting

Question 18

What are the gills of protobranchs used for?

Answer 18

Solely respiration

Question 19

Explain the filter feeding mechanism of lamellibranchs

Answer 19

Use gills to trap food particles
No palp proboscis but retained labial palps
Larger gill surface area
Gills made up of filaments with inter-filamentary spaces between them to allow water flow

Question 20

Describe the gills of lamellibranch bivalves.

Answer 20

GIlls evolved from those of protobranchs
Expanded by increasing number and length of filaments
W-shape reduces overall size/volume while increasing surface area
Two gills with W-shape (Each half is a demibranch)
Surface of gill often termed gill lamellae

Question 21

What 3 different type of cilia are used for feeding in bivalves?

Answer 21

Lateral cilia
Lateral-frontal cilia
Frontal cilia

Question 22

What is the function of lateral cilia in bivalve feeding?

Answer 22

Create water current and aid respiration

Question 23

What is the function of lateral-frontal cilia in bivalve feeding?

Answer 23

Form mesh to catch food, pass particles to frontal cilia. Have a lesser role in creating water flow.

Question 24

What is the function of frontal cilia in bivalve feeding?

Answer 24

Pass food particles captured by cilia to food groove. Food passed to labial palps then the mouth

Question 25

What do smaller species of gastropods use for locomotion?

Answer 25

Mucous secretions and cilia

Question 26

What are the disadvantages of gliding using mucous as a locomotory technique?

Answer 26

Slow ~1-3mm/sec
Not energy efficient ~35% of metabolic cost

Question 27

What do larger species of gastropods use for locomotion?

Answer 27

Muscular contraction in conjunction with a hydrostatic skeleton - contraction of muscles causes liquid in haemocoelic spaces to change shape causing movement

Question 28

What muscle lies dorso-ventrally and acts antagonistically on the foot and head of gastropods?

Answer 28

Columellar muscle

Question 29

Describe the columellar muscle of gastropods.

Answer 29

Lies dorso-ventrally and acts antagonistically on the head/foot

Question 30

What muscle lies longitudinally and transverse across the foot and is used for locomotion and prey capture?

Answer 30

Tarsos muscles

Question 31

Describe the tarsos muscles of gastropods.

Answer 31

Lies longitudinally and transverse across the foot, involved in locomotion and prey capture

Question 32

What are the 3 types of waves of muscle contraction which can be employed by gastropods?

Answer 32

Direct waves that move in direction of locomotion
Retrograde waves that move opposite to direction of locomotion
Ditaxic waves - two waves that can be direct or retrograde

Question 33

Explain the steps in bivalve burrowing.

Answer 33

1. Pedal retractor and shell adductor muscles relax
2. Circular muscles contract - lengthening of foot
3. Further contraction forces blood into terminal anchor of the foot
4. Siphons close and water is expelled to soften substrate
5. Anterior pedal retractor contracts, rocking the dorsal side of shell downwards
6. Posterior pedal retractor contracts, rocking the ventral side of the shell downwards