Mollusks Kristin Marquardt What is a Mollusk A

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

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 • http: //www. assateague. com/nt-bival. html • http: //www. butterflyrevolt. com/characteristics-ofmollusks. html • http: //www. marietta. edu/~biol/mussels/reprod. ht ml • http: //www. bumblebee. org/invertebrates/MOLLU SCA. htm • http: //news. nationalgeographic. com/news/2008/ 04/080430 -AP-new-zealand. html • Biology: Principles & Explorations (our text book)