Chapter 2 Mollusks, Arthropods, and Echinoderms

1. Chapter 2 Mollusks, Arthropods, and Echinoderms Section 1 – Mollusks (Gastropods, Bivalves, and Cephalopods)

2. Characteristics of Mollusks • Examples: clams, oysters, scallops, snails, squids • Invertebrates with soft, unsegmented bodies that are often protected by a hard outer shell.

3. Characteristics of Mollusks – cont. • Thin layer of tissue called a mantle that covers its internal organs • Biologists classify mollusks into groups based on their physical characteristics: shell, type of shell, type of foot, type of nervous system

4. Body Structure • Bilateral symmetry • Digestive system with 2 openings • Body parts are not repeated – internal organs are located together in one area

5. Circulatory System • Most have an open Circulatory System – blood is not always inside blood vessels • Blood sloshes over the organs and returns to the heart

6. Obtaining Oxygen • Most mollusks that live in water have gills • Gills have cilia and a rich supply of blood vessels • Carbon dioxide, a waste gas, moves out of the blood and into the water

7. Snails and Slugs • Gastropods are the largest group of mollusks • Live in oceans, rocky shores, fresh water, on land • Have a single external shell or no shell at all

8. Obtaining Food • Some are herbivores, scavengers, carnivores • Use a radula to obtain food • Herbivores – sandpaper to tear through plant tissue • Carnivores – drill a hole, scrapes

9. Movement • Creeps along on a broad foot • Foot oozes a carpet of slippery mucus which helps make it easier for the gastropod to move

10. Two-Shelled Mollusks • Bivalves – are mollusks that have 2 shells held together by hinges and strong muscles • Examples: oysters, clams, scallops, mussels • Found in all kinds of watery environments

11. Obtaining Food • Filter feeders that strain tiny organisms from water • Capture food as water flows over their gills, food sticks to the mucus that covers the gills, cilia move the food particles into it’s mouth • Most bivalves are omnivores

12. Movement • Don’t move quickly • Larvae – float or swim Adults – stay in 1 place or use their foot • Oysters and mussels attach themselves to rocks • Clams move

13. Protection • Sand gets stuck between a bivalve’s mantle and shell – it irritates the soft mantle – mantle produces a smooth, pearly coat to cover the object • Sometimes a pearl forms

14. Octopuses and Their Relatives • Cephalopods are ocean-dwelling mollusks whose foot is adapted to form tentacles around its mouth. • Examples are:octopuses, squid, nautiluses, cuttlefishes

15. Obtaining Food • Carnivores - uses tentacles to capture the food and crush it • Tentacles have suckers that receive sensations of taste and touch • It doesn’t have to touch something to taste it because the suckers respond to chemical in the water – tastes before touching it

16. Nervous System • Large eyes – excellent vision • Most complex nervous system of any invertebrate • Large brains – can remember and learn

17. Movement • Swim by jet propulsion • Squeeze a current of water out of the mantle cavity and through a tube • Turning the tube changes the direction they’re going