Molluscs!
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
Trochophore larvae also seen in Annelids (segmented worms) So… Annelids & Molluscs may have evolved from the ancestor!
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
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
Special Features (cont…) Varies from primitive (ex. Clams) to advanced (ex. Octopi) RESPONSE
Special Features (cont…) Most have separate sexes & external fertilization (release eggs & sperm) Some are HERMAPHRODITES (ex. Snails & some bivalves) REPRODUCTION
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!
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
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
A typical Gastropod
A close up of the radula
Some Examples… Land slugs/snails Ocean snails Nudibranchs (sea slugs) Abalones
Class Bivalva Class Bivalva
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
Clam Diagram…
More Info… Most sessile, although some (ex. Scallops) are fast swimmers Mantle manufactures shell made of calcium carbonate & maintains it
Making a Pearl Grain of sand gets caught in shell & coated with mantle secretions Builds up to form a pearl!
Helpful & Harmful Molluscs Molluscs in our world
Detritus Feeders Clean up dead or decaying organic material
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
Shellfish are YUMMY! Used as an important food source for many animals
Crop Damage Slugs & snails feed on agricultural plants & in gardens
Shipworms Use radula to “drill” through wood in water damage to boats & docks
Shellfish Poisoning Filter feeders (ex. Clams & oysters) build up dangerous levels of toxic protists (“red tide”) When ingested, can cause paralysis or death