Phylum Mollusca (Chapter 27.4)

1. Phylum Mollusca (Chapter 27.4) Please set up your notebook for Cornell Notes

2. Mollusks • Characteristics • Soft-bodied w/ external or internal shell • Have a free swimming larval stage called trochophore • Also appear in annelids

3. Form and function • Body plan • Bilaterally symmetrical • Four parts • Foot  flat structure for crawling, shovel-shaped for burrowing or tentacles for capturing prey • Mantle  thin layer of tissue that covers the body • Shell  made by glands in the mantle that secrete calcium carbonate • Reduced or lost in some groups • Visceral mass  internal organs

5. Feeding • Herbivores, carnivores, filter feeders, detritivores or parasites • Snails and slugs have a raspy, tongue shaped structure known as a radula • Can scrape algae off rocks, drill thru shells and tear tissues • Octopi and some sea slugs use sharp jaws to eat • Some octopi use poison to subdue prey • Clams, oysters and scallops are filter feeders • Siphon  a tube-like structure that brings water in and out of the body

6. Respiration • Aquatic mollusks use gills inside the mantle cavity • Terrestrial mollusks use a large mantle cavity lined with blood vessels • Lining must be moist • Circulation • Some mollusks have an open circulatory system (ie. Snails and clams) • Other mollusks have a closed circulatory system (ie. Octopi and squid)

7. Excretion • Nephridia remove ammonia from the blood and release it outside of the body • Response • Simple nervous system  small ganglia, few nerve cords and eyespots • Clams, oysters • Complex nervous system  well developed brains and can remember things for long periods • Octopi, squid, cuttlefish

9. Movement • Snails secrete mucus along base of foot then use rippling motion • Octopi use jet propulsion by drawing water into mantle and expelling from siphon • Reproduction • Sexual • External fertilization  release large number of eggs and sperm into water • Snails and two shelled mollusks • Internal fertilization • Tentacled mollusks and some snails • Some mollusks are hermaphrodites but fertilize other organisms eggs

10. Classes of mollusks • Class Gastropoda shell-less or single shelled, move by using foot on ventral surface • Snails, slugs, nudibranches (sea slugs) • Nudibranches recycle nematocysts from cnidarians to use for protection • Snails withdraw into shell for protection

11. Class Bivalvia two shelled mollusks • Clams, oysters, mussels, scallops • Tend to stay in one place • Filter feeders

12. Class Cephalopoda soft-bodied, head attached to a foot that is divided into tentacles • Octopi, cuttlefish, squid, nautilus • Small internal shell or no shell • The only cephalopod with shell is a nautilus • Large eyes