1. End Show Slide 1 of 43 Copyright Pearson Prentice Hall Biology

2. End Show Slide 2 of 43 Copyright Pearson Prentice Hall 27-4 Mollusks

3. End Show 27-4 Mollusks Slide 3 of 43 Copyright Pearson Prentice Hall What Is a Mollusk? What are the defining features of mollusks?

4. End Show 27-4 Mollusks Slide 4 of 43 Copyright Pearson Prentice Hall What Is a Mollusk? Mollusks are soft-bodied animals that usually have an internal or external shell. Mollusks include snails, slugs, clams, squids, and octopi. Many mollusks share similar developmental stages.

5. End Show 27-4 Mollusks Slide 5 of 43 Copyright Pearson Prentice Hall What Is a Mollusk? Many aquatic mollusks have a free-swimming larval stage called a trochophore. The trochophore larva is also characteristic of annelids, indicating that these two groups may be closely related.

6. End Show 27-4 Mollusks Slide 6 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Mollusks have complex, interrelated organ systems that function together to maintain the body as a whole.

7. End Show 27-4 Mollusks Slide 7 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks What is the basic body plan of mollusks?

8. End Show 27-4 Mollusks Slide 8 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Body Plan The body plan of most mollusks has four parts: foot, mantle, shell, and visceral mass.

9. End Show 27-4 Mollusks Slide 9 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks The muscular foot takes many forms flat structures for crawling spade-shaped structures for burrowing tentacles for capturing prey Snail Clam Squid

10. End Show 27-4 Mollusks Slide 10 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks The mantle is a thin layer of tissue that covers most of the mollusk's body. The shell is made by glands in the mantle that secrete calcium carbonate. Just beneath the mantle is the visceral mass, which contains the internal organs.

11. End Show 27-4 Mollusks Slide 11 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Feeding Mollusks can be herbivores, carnivores, filter feeders, detritivores, or parasites.

12. End Show 27-4 Mollusks Slide 12 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Snails and slugs feed using a flexible, tongue- shaped structure known as a radula. Hundreds of tiny teeth are attached to the radula. The radula is used to scrape algae off rocks or to eat the soft tissues of plants. Teeth Radula

13. End Show 27-4 Mollusks Slide 13 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Clams, oysters, and scallops use gills. Food is carried by water, which enters the incurrent siphon. A siphon is a tubelike structure through which water enters and leaves the body.

14. End Show 27-4 Mollusks Slide 14 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks The water flows over the gills and leaves by the excurrent siphon. Excurrent siphon Incurrent siphon

15. End Show 27-4 Mollusks Slide 15 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Respiration Aquatic mollusks breathe using gills inside their mantle cavity. Gills

16. End Show 27-4 Mollusks Slide 16 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks As water passes through the mantle cavity, oxygen in the water moves into blood flowing through the gills. At the same time, carbon dioxide moves in the opposite direction.

17. End Show 27-4 Mollusks Slide 17 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Land snails and slugs respire using a mantle cavity that has a large surface area lined with blood vessels.

18. End Show 27-4 Mollusks Slide 18 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Circulation Some mollusks have open circulatory systems; other mollusks have closed circulatory systems.

19. End Show 27-4 Mollusks Slide 19 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks In an open circulatory system, blood is pumped through vessels by a simple heart. Heart

20. End Show 27-4 Mollusks Slide 20 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Blood leaves the vessels and works its way through different sinuses. Blood passes from the sinuses to the gills, where oxygen and carbon dioxide are exchanged. Blood is then pumped back to the heart. Slow-moving mollusks often have open circulatory systems.

21. End Show 27-4 Mollusks Slide 21 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Faster-moving mollusks have a closed circulatory system. A closed circulatory system can transport blood through an animal’s body much more quickly than an open circulatory system.

22. End Show 27-4 Mollusks Slide 22 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Excretion Cells of the body release nitrogen-containing waste into the blood in the form of ammonia.

23. End Show 27-4 Mollusks Slide 23 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Nephridia remove ammonia from the blood and release it outside the body. Nephridium

24. End Show 27-4 Mollusks Slide 24 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Response The complexity of the nervous system and the ability to respond to environmental conditions varies among mollusks. Two-shelled mollusks have a simple nervous system.

25. End Show 27-4 Mollusks Slide 25 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Octopi and their relatives have the most highly developed nervous system of all invertebrates. Well-developed brains in these animals allows them to remember things for long periods.

26. End Show 27-4 Mollusks Slide 26 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Movement Snails secrete mucus along the base of the foot, and then move over surfaces using a rippling motion of the foot. The octopus draws water into the mantle cavity and then forces the water out through a siphon. Water leaving the body propels the octopus in the opposite direction.

27. End Show 27-4 Mollusks Slide 27 of 43 Copyright Pearson Prentice Hall Form and Function in Mollusks Reproduction Some mollusks reproduce sexually by external fertilization. In other mollusks, fertilization takes place inside the body of the female. Some mollusks are hermaphrodites and usually fertilize eggs from another individual.

28. End Show 27-4 Mollusks Slide 28 of 43 Copyright Pearson Prentice Hall Groups of Mollusks What are the characteristics of the three main classes of mollusks?

29. End Show 27-4 Mollusks Slide 29 of 43 Copyright Pearson Prentice Hall Groups of Mollusks The three major classes of mollusks are gastropods bivalves cephalopods

30. End Show 27-4 Mollusks Slide 30 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Gastropods Gastropods are shell-less or single- shelled mollusks that move by using a muscular foot located on the ventral side. Many gastropods have a single shell that protects their bodies. When threatened, they can pull completely into their shells.

31. End Show 27-4 Mollusks Slide 31 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Gastropods include pond snails land slugs sea butterflies sea hares limpets nudibranchs

32. End Show 27-4 Mollusks Slide 32 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Bivalves Bivalves have two shells that are held together by one or two powerful muscles. Common bivalves include: clams oysters mussels scallops

33. End Show 27-4 Mollusks Slide 33 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Cephalopods Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms.

34. End Show 27-4 Mollusks Slide 34 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Cephalopods have eight or more tentacles equipped with sucking disks that grab and hold prey. Most modern cephalopods have only small internal shells or no shells at all. The only present-day cephalopods with external shells are nautiluses.

35. End Show 27-4 Mollusks Slide 35 of 43 Copyright Pearson Prentice Hall Groups of Mollusks Cephalopods have complex sense organs that help them detect and respond to external stimuli. Cephalopods distinguish shapes by sight and texture by touch. The eyes of many cephalopods are complex.

36. End Show 27-4 Mollusks Slide 36 of 43 Copyright Pearson Prentice Hall Ecology of Mollusks Mollusks feed on plants prey on animals filter algae out of the water eat detritus

37. End Show 27-4 Mollusks Slide 37 of 43 Copyright Pearson Prentice Hall Ecology of Mollusks Some mollusks are hosts to symbiotic algae or to parasites; others are themselves parasites. Mollusks are food for many organisms.

38. End Show - or - Continue to: Click to Launch: Slide 38 of 43 Copyright Pearson Prentice Hall 27-4

39. End Show Slide 39 of 43 Copyright Pearson Prentice Hall 27-4 The trochophore larva is a characteristic that mollusks share with a.flatworms. b.roundworms. c.annelids. d.flukes.

40. End Show Slide 40 of 43 Copyright Pearson Prentice Hall 27-4 Water enters and leaves the body of a bivalve through a.a siphon. b.cilia. c.a coelom. d.a nephridium.

41. End Show Slide 41 of 43 Copyright Pearson Prentice Hall 27-4 The most active group of mollusks is the a.gastropods. b.bivalves. c.cephalopods. d.shell-less gastropods.

42. End Show Slide 42 of 43 Copyright Pearson Prentice Hall 27-4 Unlike the other mollusks, cephalopods have a(an) a.closed circulatory system. b.ventral blood vessel. c.open circulatory system. d.dorsal blood vessel.

43. End Show Slide 43 of 43 Copyright Pearson Prentice Hall 27-4 The body plan of most mollusks includes all of the following EXCEPT a a.foot. b.mantle. c.shell. d.radula.

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