1. Chapter 27 Mollusks and Segmented Worms

2. Chapter 27 27.1 Mollusks –A. What is a Mollusk? 1. Slugs, snails, squids, and animals that once lived in shells in the ocean a. Most live in ocean, but some live in fresh water and moist terrestrial habitats 2. Phylum - Mollusca

3. Chapter 27 A. What are Mollusks? ( cont ) –3. Classes Shell-less, hinged shells, and single shell –4. Have bilateral symmetry, a coelom, two body openings, a muscular foot, and a mantle

4. Chapter 27 B. Benefits of coelom: 1 Separates muscles of gut from those of body wall allowing food to move through the body independent of locomotion 2. Allows space for circulatory system to function without interference from other organs 3. In some species, the fluids in the coelom act as a hydrostatic skeleton for the muscles to contract against

5. Chapter 27 C. How mollusks obtain food –1. Have a radula – tongue-like organ with rows of teeth that drill, scrape, grate or cut food –2. Then pull food into mouth –3. Bivalves obtain food by filtering it out of the water

6. Chapter 27 D. Reproduction in Mollusks –1. Separate sexes and reproduce sexually A. Egg and sperm released at the same time into the water where external fertilization takes place B. Gastropods are hermaphrodites C. Form larva called trochophore - pear shaped larva with cilia protruding out each end –1 Cilia propel larva and push food into mouth –2 Free swimming larva aid in dispersal

7. Chapter 27 E. Systems of body –1. Nervous - simple system of brain and nerves that coordinate their movement and behavior Paired eyes –2. Circulation Well-developed, three chambered heart, which pumps blood into an open circulatory system

8. Chapter 27 E. Systems ( cont ) –3. Respiration A have gills for respiration B gases can diffuse C some land snails had their mantle cavity evolved into primitive lung

9. Chapter 27 E. Systems ( cont ) –4. Excretion A. Oldest known creatures with excretion structures B. Nephridia remove metabolic wastes from animal –1 One or two and they collect waste from the coelom and discharge the waste by pumping the gills

10. Chapter 27 F. Diversity of Mollusks –1. Gastropoda largest and most diverse class A. Have one shell B. Body plan based on “Torsion” twisting of the body, allowing it to withdraw it’s head C. Movement is by wave-like action D. Two eyes at end of tentacles

11. Chapter 27 F. Diversity ( cont ) 2. Bivalvia –A. Most are sessile and filter feeders –B. Two valves or shells 1 1st layer thin outer that protects shell from acid 2 2nd layer thick layer of calcium carbonate for strength 3 3 rd layer smooth protects the animals soft body ( pearl may develop )

12. Chapter 27 nnn F. Diversity ( cont ) –3. Cephalopoda octopus A. Name means Head-Foot B. Use tentacles to capture food C. Closed circulatory system D. All live in oceans E. Propelled by mantle pushing water though excurrent siphon –1 Squids can attain speeds of 20 m / sec F. Squids use ink-like substance for defense G. Have separate sexes and internal fertilization