General Information Body symmetry – BilateralBody symmetry – Bilateral Multicellular CellsMulticellular Cells Evolved from flatworms during early Cambrian Era.Evolved from flatworms during early Cambrian Era. All are Heterotrophs (feed on other living matter).All are Heterotrophs (feed on other living matter). Sea shells that people pick up are actually from the Mollusca phylum.Sea shells that people pick up are actually from the Mollusca phylum.
Distinguishing Characteristics Structures specific to MolluscaStructures specific to Mollusca –Muscular foot – Used to support forward movement. –Hard shell – Shells made up of Calcium Carbonate (CaCO 3 ). Similar body structureSimilar body structure –Head, foot, visceral mass (digestive, excretory, and reproductive organs). –Covered by mantle (significant cavity used for breathing and excursion).
Feeding and Digestion They all are heterotrophs meaning they do not produce their own food.They all are heterotrophs meaning they do not produce their own food. Most have a tongue called radula that is armed with teeth.Most have a tongue called radula that is armed with teeth. Cephalopods such as squids are sneaky predators that pounce on their prey and poison it with their saliva.Cephalopods such as squids are sneaky predators that pounce on their prey and poison it with their saliva. Bivalves filter food particles with their gills.Bivalves filter food particles with their gills. They digest nitrogen through metabolism.They digest nitrogen through metabolism.
Reproduction Reproduce sexually Protostrome – During embryo development, the mouth develops first from the blastospore. Slugs and snails are hermaphrodites. Need to mate still to fertilize egg. Other mollusks lay eggs that form into larvae.
Circulatory System Mollusks have an open circulatory system. –Means blood does not circulate through vessels but is collected from the gills, travels to heart, and back to gills to resupply oxygen. Cephalopods (squids) have closed system due to need of larger oxygen supply. The hemocoel replaced the coelom in mollusks. –Hemocoels are blood-filled cavities near the heart.
Nervous System Complex, varies from specie to specie. Cephalopods considered intelligent invertebrae. Can be compared to a domestic cat. Well developed eye sight.