Mollusks Kristin Marquardt

What is a Mollusk? A mollusk is a soft bodied animal of the phylum Mollusca, having an unsegmented body Mollusks: –Lack skeletons –Soft bodies –3-part body plan –Open blood systems (Except cephalopods) –Radula (Except bivalves)

Body Plan All mollusks have a 3-part body plan: –Muscular foot –Head –Visceral Mass (Mantle Cavity)

Types of Mollusks Mollusks are broken down into 3 major classes: –Bivalves (Scallop) –Gastropods (Slug) –Cephalopods (Octopus)

Bivalves There are about 10,000 species –Oysters, scallops, shipworms No distinct head region 2-part shell that is connected by a hinge and adductor muscles 3 layers of the shell –Tough outer layer –Thick middle layer –Smooth inner layer

Eating Habits Suck water through siphons (hollow tubes) The water goes in one siphon, the gill catches the prey, and the cilia directs food to the bivalves mouth. Then the extra water travels out the other siphon. Oysters permanently attach to rocks to feed Scallops swim as they feed, opening and closing their valves rapidly like jaws The shipworm digests cellulose in wood by protists that live inside it’s intestine

Reproduction Sexually Most born either male or female but some born hermaphroditic –Shed sperm and eggs into water, fertilization –Eggs develop –Free swimming trochophore larvae (marine) –Free swimming veliger

Gastropods About 8,000 species Snails and slugs Marine and Terrestrial Single shell Have a radula (tongue- like scraping organ) –Can be used to cut, scrape, or as a weapon Most have a pair of tentacles with eyes on top.

Gastropods Marine Gastropods –Shell can be closed like a door using a plate that pulls shell into place –Breathe with gills in the mantle cavity Except Nudibranchs Terrestrial Gastropods –Secrete mucus from base of foot –Cannot close shell –More active when air has higher moisture

Eating Mostly herbivores Use of radula –Marine gastropods scrape algae off rocks with radula Cone shells use radula as a poison tipped harpoon, shot into their prey –Terrestrial gastropods saw off leaves with radula

Changing Body!!! As the gastropod grows, it goes through torsion Torsion is a 180 degree twisting of the mantle cavity during development Gives gastropod a place to hide when threatened

Cephalopods

About 600 species Squid, Octopi, Nautiluses, and Cuttlefish Most of body is a large head attached to tentacles Marine Most intelligent of all invertebrates Most lack external shell –Nautilus The largest eye in the world is from a giant squid

Eating! All cephalopods are marine predators They eat: –Fish –Crustaceans –Worms –Other Mollusks Their tentacles have hooks or suction cups for catching their prey

Reproduction The males sperm is stored in sacs that open into the mantle cavity Males use a modified tentacle to take a packet of sperm from it’s mantle and into the female’s mantle Eggs become fertilized, leave her body, and attach to rocks

Sources mollusks.htmlhttp:// mollusks.html mlhttp:// ml SCA.htmhttp:// SCA.htm 04/ AP-new-zealand.html Biology: Principles & Explorations (our text book)