1. Introduction to Molluscs
Biology 11
Mrs. Trevelyan

2. Mollusca 1. PRESCRIBED LEARNING OUTCOMES and VOCABULARY 2. VIDEOS:
-None 
3. TEXTBOOK PGS
Section 26.1 pgs

4. Examples of Members:

5. Overview…

6. Four Classes of Mollusca

7. Gastropods (“stomach foot”)
are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side. 
many have a single shell that protects their bodies.
when threatened, they can pull completely into their shells.
Include:
pond snails
land slugs
sea butterflies
sea hares
limpets
nudibranchs

8. A close up of a snail…

9. And let’s not forget the nudibranchs…

10. Bivalves (“two shells”)
Bivalves have two shells that are held together by one or two powerful muscles. 
Common bivalves include:
clams
oysters
mussels
scallops

11. Cephalopods (“head foot”)
Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms

12. Polyplacophora (“many plates”)
Includes chitons
Have 8 articulated plates or valves
Live mostly in rocky intertidal zone
Eat algae

13. 1. Unifying Characteristics
include snails, slugs, clams, squids, and octopi
Coelomate, have cephalization, symmetry
are soft-bodied animals with developed organ systems
usually have an internal or external shell.
gills for respiration
Most have separate sexes
Many aquatic mollusks have a free-swimming larval stage called a trochophore.
can be herbivores, carnivores, filter feeders, detritivores, or parasites.

14. 2. Structure
The body plan of most mollusks has four parts: foot, mantle, shell, and visceral mass (organs)
The muscular foot takes many forms:
- flat structures for crawling
-spade-shaped structures for burrowing -tentacles for capturing prey

15. A clam dissection…

16. 3. Feeding and Digestion
Mollusks can be herbivores, carnivores, filter feeders, detritivores, or parasites.
Snails and slugs feed using a flexible, tongue-shaped structure known as a radula.
Hundreds of tiny teeth are attached to the radula.
The radula is used to scrape algae off rocks or to eat the soft tissues of plants.

17. 3. Feeding and Digestion Clams are filter feeders
The water flows over the gills and leaves by the excurrent siphon. Filtered out phytoplankton then goes to the stomach to be digested
Excurrent siphon
Incurrent siphon

18. 4. Respiration
Aquatic mollusks breathe using gills inside their mantle cavity. The water flows over the gills and leaves by the excurrent siphon.
Terrestrial mollusks breath using their mantle cavity (ex snails) and diffusion across moist skin
Gills

19. 5. Circulation All have 1 or more hearts
Have a circulatory system: opened or closed
In an open circulatory system, blood is pumped through vessels by a simple heart.
This works well for slow moving organism, as it is not very efficient
Ex snails, clams
Heart

20. 5. Circulation
Faster moving mollusks, such as octopuses, use a CLOSED CIRCULATORY SYSTEM- blood is in blood vessels
More efficient

21. Circulatory System of an Octopus

22. Excretion
Nephridia remove liquid waste (ammonia) from the blood and release it outside the body.
Nephridium

23. 5. Nervous System
Cephalization with a developed brain in octopuses and squids
Bivalves (ex clams) do not have cephalization and do not have brains!
All have taste, touch, smell, balance
Some members have well developed eyes

24. 6. Reproduction Separate male and female
Many aquatic mollusks have a free-swimming larval stage called a trochophore.
The trochophore larva is also characteristic of annelids, indicating that these two groups may be closely related.

25. 6. Reproduction Some release sperm and egg directly into the water
Some use internal fertilization

26. These are not reproductive organs…they are siphons for breathing

27. Barnacles hold the record!

28. 7. Ecological Importance
Food source for many animals
Cuttlebone used for bird health
Jewellery and decorations from shells
Albalone
Pearls
Destructive- molluscs etc can destroy docks