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2. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep

3. Chapter 35 Mollusks and Annelids Table of Contents Section 1 Mollusca Section 2 Annelida

4. Section 1 Mollusca Chapter 35 Objectives • Describethe key characteristics of mollusks. • Describethe body plan of mollusks. • Namethe characteristics of three major classes of mollusks. • Comparethe body plans of gastropods, bivalves, and cephalopods.

5. Section 1 Mollusca Chapter 35 Characteristics of Mollusks • PhylumMollusca is a diverse group of invertebrates such as clams, snails, slugs, squids, and octopuses. • They are called mollusks, from the Latin molluscus, which means “soft.” Many mollusks have soft bodies and some have a hard shell. • Some mollusks are sedentary filter feeders, while others are fast-moving predators. • Mollusks are coelomates. • Most aquatic mollusks and annelids have a larval stage called a trochophore.

6. Section 1 Mollusca Chapter 35 Body Plan of Mollusks • The body of a mollusk is generally divided into: • the visceralmass, which contains the heart and the organs of digestion, excretion, and reproduction • the head-foot, which consists of: • the head, which contains the mouth and sensory structures • the foot, a large, muscular organ for locomotion • The coelom is limited to a space around the heart. • A layer of epidermis called the mantle covers the visceral mass.

7. Section 1 Mollusca Chapter 35 Body Plan of Mollusks, continued • In most mollusks, the mantle secretes one or more hard shells containing calcium carbonate. • This disadvantage of a shell is offset by having gills. • The gills are protected within the mantle cavity. • Most mollusks are bilaterally symmetrical. • The nervous system consists of paired clusters of nerve cells called ganglia. • The main feeding adaptation of many mollusks is the radula.

8. Section 1 Mollusca Chapter 35 Class Gastropoda • The largest and most diverse class of mollusks is Gastropoda, whose members are called gastropods. • Most gastropods, including snails, abalones, and conchs, have a single shell. Others, such as slugs and nudibranchs, have no shell. • Gastropods undergo the process of torsion during larval development. • Gastropods have an open circulatory system in which a heart pumps hemolymph from gills or lungs into the hemocoel.

9. Section 1 Mollusca Chapter 35 Class Gastropoda, continued Snails • Snails live in moist and aquatic environments. • Most snails locate food using eyes at the end of tentacles. • Snails survive dry periods by retreating into their shells and sealing the opening with a mucous plug. Other Gastropods • Slugs are terrestrial and lack shells. • Nudibranchs are marine and lack shells. • Pteropods, or “sea butterflies,” have a foot that is modified into a winglike flap and used for swimming rather than crawling.

10. Section 1 Mollusca Chapter 35 Class Bivalvia • The class Bivalvia includes aquatic mollusks such as clams, oysters, and scallops. • They are called bivalves because their shell is divided into two valves connected by a hinge. • Each valve consists of three layers. • Most bivalves are sessile filter feeders. • Bivalves lack a distinct head and have three pairs of nerve ganglia.

11. Section 1 Mollusca Chapter 35 Class Bivalvia, continued Clams • Clams are bivalves that live buried in mud or sand. • The mantle cavity of a clam is sealed except for a pair of hollow, fleshy tubes called siphons. • Water enters through the incurrent siphon. • Water leaves through the excurrent siphon. Other Bivalves • Oysters become attached to a hard surface early in their development. • Scallops can move through the water by repeatedly opening their valves and snapping them shut.

12. Section 1 Mollusca Chapter 35 Class Cephalopoda • The class Cephalopoda includes octopuses, squids, cuttlefishes, and chambered nautiluses. • They are called cephalopods, which means “head-foot.” • They are specialized as free-swimming predators. • They have tentacles and beaklike jaws on the head. • Their nervous system is very advanced. • They have a closed circulatory system. • Many use pigments to hide and disguise themselves.

13. Section 1 Mollusca Chapter 35 Class Cephalopoda, continued Squids • Squids are cephalopods with ten tentacles. • They propels themselves by pumping jets of water with the mantle through an excurrent siphon. Octopuses • Octopuses have eight tentacles and are similar to squids. • They often crawl along the ocean bottom or lie in wait for prey. Chambered Nautiluses • The chambered nautilus is the only existing cephalopod that has retained its external shell. • The shell is coiled and divided into a series of chambers. The body is confined to the outermost chamber.

14. Section 1 Mollusca Chapter 35 Mollusk Body Plan

15. Section 1 Mollusca Chapter 35 Characteristics of Mollusks

16. Section 1 Mollusca Chapter 35 Anatomy of a Trochophore

17. Section 1 Mollusca Chapter 35 Anatomy of a Mollusk

18. Section 1 Mollusca Chapter 35 Radula

19. Section 1 Mollusca Chapter 35 Types of Mollusks

20. Section 1 Mollusca Chapter 35 Characteristics of Gastropods

21. Section 1 Mollusca Chapter 35 Anatomy of a Snail

22. Section 1 Mollusca Chapter 35 Characteristics of Bivalves

23. Section 1 Mollusca Chapter 35 Anatomy of a Clam

24. Section 1 Mollusca Chapter 35 Characteristics of Cephalopods

25. Section 2 Annelida Chapter 35 Objectives • Identifythe structures that provide the basis for dividing annelids into three classes. • Listthe advantages of body segmentation. • Describethe structural adaptations of earthworms. • Comparethe three classes of annelids.

26. Section 2 Annelida Chapter 35 Characteristics of Annelids • The phylum Annelida is made up of bilaterally symmetrical, segmented worms. • This phylum includes common earthworms, feather-duster worms, and bloodsucking leeches. • They are called annelids, which means “little rings” and refers to the many body segments. • Annelids have a true coelom that is divided into separate compartments by partitions. • Most annelids have external bristles called setae(singular, seta), and some have fleshy protrusions called parapodia (singular, parapodium).

27. Section 2 Annelida Chapter 35 Class Oligochaeta • Annelids of the class Oligochaeta generally live in the soil or in fresh water and have no parapodia. • Oligochaeta means “few bristles”; these annelids have a few setae on each segment. • The most familiar member is the earthworm. Structure and Movement • An earthworm’s body has over 100 nearly-identical segments. • Circular and longitudinal muscles line the interior body wall. • Locomotion is made possible by segmentation.

28. Section 2 Annelida Chapter 35 Class Oligochaeta, continued Feeding and Digestion • Earthworms ingest soil as they burrow through it. • Soil is moved through these structures: • mouth • pharynx • esophagus • crop • gizzard • intestine • includes the typhlosole • anus • Earthworms play an important role in the condition of soil.

29. Section 2 Annelida Chapter 35 Class Oligochaeta, continued Circulation • Contractions of the aorticarches and the dorsal blood vessel force blood through the closed circulatory system. Respiration and Excretion • Oxygen and carbon dioxide diffuse through the skin, which contains many small blood vessels and must be kept moist. • Cellular wastes and excess water are excreted through nephridia. Neural Control • The nervous system of an earthworm consists of a chain of ganglia connected by a ventral nerve cord. • Sensory structures are found in all segments but are concentrated at the anterior end.

30. Section 2 Annelida Chapter 35 Class Oligochaeta, continued Reproduction • Earthworms are hermaphrodites, but an individual worm cannot fertilize its own eggs. • During mating, earthworms press their ventral surfaces together. • They are held together by their setae and by a film of mucus secreted by each worm’s clitellum. • The sperm from each worm move through the mucus to the seminal receptacle of the other. • The clitellum secretes a tube of mucus and chitin. • Fertilization occurs inside the tube, which forms a protective case for the young worms.

31. Section 2 Annelida Chapter 35 Class Polychaeta and Hirudinea • Most annelids are members of the class Polychaeta, which means “many bristles.” • Polychaetes differ from other annelids in that they have antennae and specialized mouthparts. • They are the only annelids that have a trochophore stage. • Hirudinea is the smallest class of annelids, consisting of about 500 species of leeches. • Leeches have no setae or parapodia. • Many leeches are carnivores but some are parasites that suck blood from other animals.

32. Section 2 Annelida Chapter 35 Anatomy of the Earthworm

33. Section 2 Annelida Chapter 35 Characteristics of Annelids

34. Section 2 Annelida Chapter 35 Segmentation

35. Section 2 Annelida Chapter 35 Types of Annelids

36. Section 2 Annelida Chapter 35 Anatomy of an Earthworm

37. Section 2 Annelida Chapter 35 Movement of an Earthworm

38. Section 2 Annelida Chapter 35 Feeding Habits of an Earthworm

39. Chapter 35 Standardized Test Prep Multiple Choice 1. Why do terrestrial snails and slugs need an environment with a high moisture content? A. to avoid drying out B. to see and hear better C. to swim more efficiently D. to avoid being eaten by birds

40. Chapter 35 Standardized Test Prep Multiple Choice, continued 1. Why do terrestrial snails and slugs need an environment with a high moisture content? A. to avoid drying out B. to see and hear better C. to swim more efficiently D. to avoid being eaten by birds

41. Chapter 35 Standardized Test Prep Multiple Choice, continued 2. Which of the following are the only mollusks with a closed circulatory system? F. snails G. bivalves H. gastropods J. cephalopods

42. Chapter 35 Standardized Test Prep Multiple Choice, continued 2. Which of the following are the only mollusks with a closed circulatory system? F. snails G. bivalves H. gastropods J. cephalopods

43. Chapter 35 Standardized Test Prep Multiple Choice, continued 3. Annelids are divided into three classes based partly on the number of which of the following? A. setae B. segments C. nephridia D. aortic arches

44. Chapter 35 Standardized Test Prep Multiple Choice, continued 3. Annelids are divided into three classes based partly on the number of which of the following? A. setae B. segments C. nephridia D. aortic arches

45. Chapter 35 Standardized Test Prep Multiple Choice, continued 4. Parapodia are distinguishing characteristics of which class of annelids? F. Bivalvia G. Hirudinea H. Polychaeta J. Oligochaeta

46. Chapter 35 Standardized Test Prep Multiple Choice, continued 4. Parapodia are distinguishing characteristics of which class of annelids? F. Bivalvia G. Hirudinea H. Polychaeta J. Oligochaeta

47. Chapter 35 Standardized Test Prep Multiple Choice, continued The diagram below shows the internal structure of a bivalve. Use the diagram to answer the questions that follow.

48. Chapter 35 Standardized Test Prep Multiple Choice, continued 5. Which of the structures is involved in respiration and feeding? A. A B. B C. C D. D

49. Chapter 35 Standardized Test Prep Multiple Choice, continued 5. Which of the structures is involved in respiration and feeding? A. A B. B C. C D. D

50. Chapter 35 Standardized Test Prep Multiple Choice, continued 6. What is structure B? F. a gill G. a siphon H. the mantle J. an adductor muscle