Phylum: Mollusca

1. Phylum:Mollusca

2. Contains over 100,000 species, making it the 2nd largest animal phylum Includes: snails, chitons, clams, slugs and squids General Information

3. Snails, clams and squid look nothing alike, but they have a few shared features • These common features are: • Foot • Mantle • Radula Shared Features

4. A muscular organ, shaped and used differently by different species • Used for digging, grasping, or creeping • Examples: • Pelecypoda (Bivalvia) – “hatchet – shaped foot” • Clams & Oysters - use the foot for digging • Gastropoda – “Stomach foot” • Snails – use the foot to crawl; stomach is in the foot • Cephalopoda – “Head foot” • Octopi and Squids – foot is modified into tentacles that attach to the head; used for moving, grasping, holding, sinking ships… The Foot

5. The mantle produces the shell and creates the color patterns in most mollusks • The shell is an exoskeleton, even if its covered, and grows with the mollusk • Examples: • A chiton’s mantle produces jointed plates that allow it to curl up into a ball and to move flexibly • Bivalves produce two shells hinged at the top • Snails (Gastropoda) produce a single, spiral-shaped shell • The mantle is inside the shell, so it can’t be seen • In other types of gastropods the mantle covers the outside of the shell, making it look shiny and new in appearance • In Cephalopods and some gastropods (like sea hares), the shell is very small and the mantle completely covers it • Nudibranchs (sea slugs) are shell-less gastropods Mantle & Shell

6. See Fig 6-2 & 6-3 • Radula – specially adapted rasp-like tongue • Proboscis – an extension of the mouth • Examples: • Herbivorous snails have a mouth with radula containing many rows, each with 5-7 complex teeth • Use the radula like a file • Carnivorous snails (ex: cone shells) have hollow, barbed, radular teeth (like harpoons) that they thrust into their prey and inject venom through them • These barbs shoot out through the proboscis • Some cone shell venom is strong enough to kill humans Radula

7. Foot • Clams – their hatchet-shaped foot is used for moving and burrowing in mud or sand • Oyster & mussels – smaller foot used for attaching themselves to a hard substrate • Scallops – don’t use foot for moving; they clap their shells together to move by jet propulsion • Siphons • Two tubes that allow water to enter and exit the bivalve • Water coming in is oxygen and nutrient rich • The water flows across the gills, O2 and CO2 are exchanged and food particles are trapped by mucus • Cilia • Tiny, hair-like structures that move trapped food towards the mouth • Located on the gills • Palps • Lip-like structures help sort the food and direct it to the mouth * See Table 6-1 for a glossary for more bivalve anatomy Marine Bivalve Anatomy

8. Pearls • In some bivalves (like oysters) irritating particles (indigestible food particles and sand) get lodged between the shell and mantle • The bivalve will then begin secreting a pearly substance called nacre • These layers of nacre eventually form pearls • Food • Many bivalves are valued as a food source • They can be very sensitive to the environment; they themselves are not sensitive to the toxicity; but they absorb it into their tissues which is then transferred to the consumer Commercialism