Feeding and Locomotion in Molluscs Flashcards
What feeding method does the generalised mollusc use?
Browser/grazer - e.g. common limpet scraping algae off rocks
What molluscs do not have a radula?
Solenogastres and bivalves
What feeding methods are seen in molluscs?
- Herbivores
- Carnivores
- Suspension
- Deposit
- Parasites
Explain the radula.
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.
What are the radular teeth tipped with in some species?
Iron oxide, calcium or silica
Which gastropods are herbivorous?
Majority of pulmonates - slugs and snails
Some marine and freshwater prosobranchs
Some opisthobranchs - sea slugs, sea hares
What is the radula of herbivorous gastropods designed for and what does it look like?
To scrape and rasp food from plants or hard substrate
Lots of rows of many small teeth
Give an example of a herbivorous gastropod and describe its feeding method.
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
What is kleptoplasty?
Kleptoplasty involves the ingestion and retention of intact chloroplasts from ingested algae.
What gastropods are carnivorous?
Most common in marine prosobranchs and opisthobranchs, very few pulmonates
What are the adaptations of the radula to a carnivorous diet in gastropods?
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
Give an example of a venomous carnivorous gastropod and explain its feeding mechanism.
Cone snail
Use a modified radular tooth which can be extended using the proboscis to deliver venom to predators
Give another example of a carnivorous gastropod.
Dog whelk
What ae the 3 major morphological groups of bivalves?
Protobranchs
Lamellibranchs
Septibranchs
What is the only group of molluscs where no species have a radula?
Bivalves
What is the feeding mechanism of bivalves?
Use gills or other organs to obtain food
Most are suspension feeders (lamellibranchs) but some are deposit feeders (protobranchs)
Explain the deposit feeding mechanism of protobranchs.
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
What are the gills of protobranchs used for?
Solely respiration
Explain the filter feeding mechanism of lamellibranchs
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
Describe the gills of lamellibranch bivalves.
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
What 3 different type of cilia are used for feeding in bivalves?
Lateral cilia
Lateral-frontal cilia
Frontal cilia
What is the function of lateral cilia in bivalve feeding?
Create water current and aid respiration
What is the function of lateral-frontal cilia in bivalve feeding?
Form mesh to catch food, pass particles to frontal cilia. Have a lesser role in creating water flow.
What is the function of frontal cilia in bivalve feeding?
Pass food particles captured by cilia to food groove. Food passed to labial palps then the mouth
What do smaller species of gastropods use for locomotion?
Mucous secretions and cilia
What are the disadvantages of gliding using mucous as a locomotory technique?
Slow ~1-3mm/sec
Not energy efficient ~35% of metabolic cost
What do larger species of gastropods use for locomotion?
Muscular contraction in conjunction with a hydrostatic skeleton - contraction of muscles causes liquid in haemocoelic spaces to change shape causing movement
What muscle lies dorso-ventrally and acts antagonistically on the foot and head of gastropods?
Columellar muscle
Describe the columellar muscle of gastropods.
Lies dorso-ventrally and acts antagonistically on the head/foot
What muscle lies longitudinally and transverse across the foot and is used for locomotion and prey capture?
Tarsos muscles
Describe the tarsos muscles of gastropods.
Lies longitudinally and transverse across the foot, involved in locomotion and prey capture
What are the 3 types of waves of muscle contraction which can be employed by gastropods?
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
Explain the steps in bivalve burrowing.
- Pedal retractor and shell adductor muscles relax
- Circular muscles contract - lengthening of foot
- Further contraction forces blood into terminal anchor of the foot
- Siphons close and water is expelled to soften substrate
- Anterior pedal retractor contracts, rocking the dorsal side of shell downwards
- Posterior pedal retractor contracts, rocking the ventral side of the shell downwards
