1. Molluscs!

2. Molluscs are Special Phylum MOLLUSCA Soft bodied
Internal or external shell
Share similar developmental pattern  most have a larval form (TROCHOPHORE) which is a free swimming form

3. Trochophore larvae also seen in Annelids (segmented worms)
So… Annelids & Molluscs may have evolved from the ancestor!

4. Basic Mollusc Form Foot: contains mouth; helps movement
Mantle: delicate layer of tissue
Shell: hard protective layer of calcium carbonate
Visceral Mass: contains inner organs; under mantle

5. Special Features
Diverse group (herbivores, carnivores, filter/detritus feeders, parasites)
Gills: Sift through food in water
Radula: Rough “teeth”; can scrape algae or drill through prey
Jaws: Bite prey (ex. Octopi)
Gills in aquatic molluscs (inside mantle)
Land molluscs have a folded mantle lined with blood vessels to diffuse O2 & CO2  kept moist at all times
FEEDING
RESPIRATION

6. Special Features (cont…)
Varies from primitive (ex. Clams) to advanced (ex. Octopi)
RESPONSE

7. Special Features (cont…)
Most have separate sexes & external fertilization (release eggs & sperm)
Some are HERMAPHRODITES (ex. Snails & some bivalves)
REPRODUCTION

8. 1. Class GASTROPODA Gastro = “stomach” Poda = “foot” Special Features
Move with a broad muscular foot on ventral side
Protective shell… BUT… slugs & nudibranchs don’t have one!

9. Nudibranchs
Detract predators by displaying bright colours (sign of “poison”)  will be bad tasting or toxic
Some use nematocysts
Slugs
Avoid predation by staying under rocks & feeding at night

10. Wacky Gastropods! Some “sea hares” squirt ink to confuse predators
Some gastropods (ex. Sea butterflies) escape predators by swimming
Muscular foot retracts into shell to seal off from predators

11. A typical Gastropod

12. A close up of the radula

13. Some Examples… Land slugs/snails Ocean snails Nudibranchs (sea slugs)
Abalones

14. Class Bivalva
Class Bivalva

15. Bi = “two”
Valva = “shell”
Have 2 shells hinged at the back & held together with 1-2 strong muscles
Begin as free swimming larvae
Some (ex. Clams) burrow into sand; others attach to a substrate (ex. Mussels) with sticky thread

16. Clam Diagram…

17. More Info…
Most sessile, although some (ex. Scallops) are fast swimmers
Mantle manufactures shell made of calcium carbonate & maintains it

18. Making a Pearl
Grain of sand gets caught in shell & coated with mantle secretions
Builds up to form a pearl!

19. Helpful & Harmful Molluscs
Molluscs in our world

20. Detritus Feeders
Clean up dead or decaying organic material

21. Used in cancer research Development of new drugs
Medical Advances
Ex. Cone snails (treatment of chronic pain) & scallops (advances in optics/eye glasses)
Used in cancer research
Development of new drugs

22. Shellfish are YUMMY!
Used as an important food source for many animals

23. Crop Damage
Slugs & snails feed on agricultural plants & in gardens

24. Shipworms
Use radula to “drill” through wood in water  damage to boats & docks

25. Shellfish Poisoning
Filter feeders (ex. Clams & oysters) build up dangerous levels of toxic protists (“red tide”)
When ingested, can cause paralysis or death