1. Ch.13 Mollusks, Worms, Arthropods, Echinoderms
Life Science

2. Section 1 – Mollusks Learning Objectives
Identify the characteristics of mollusks.
Describe gastropods, bivalves, and cephalopods.
Explain the environmental importance of mollusks.

3. Section 1 – Mollusks
A. Mollusks – soft-bodies invertebrates with bilateral symmetry and usually one or two shells with organs in a fluid-filled cavity

4. 1. Thin layer of tissue called the mantle covers the body organs and secretes shell.
2. Mantle cavity (between soft body and mantle) contains gills.

5. 3. For most mollusks, an open circulatory system moves blood through vessels into open spaces around body organs.
4. Well-developed head has a mouth and some sensory organs.
5. Underside is a muscular foot used to move.

6. B. Mollusks are classified into three common groups based on:
shell presence
shell type
food type.

7. 1. Gastropods usually have a single shell.
a. Include snails, conchs, and garden slugs
b. Use radula (a tongue-like organ with rows of teeth) to get food
c. Some have foot glands that secret a layer of mucus for sliding

9. 2. Bivalves have a hinged, two-part shell and include clams, oysters, and scallops.

10. 3. Cephalopods are the most specialized and complex mollusks.
a. Include squid, octopuses, cuttlefish, and chambered nautiluses
b. Cephalopods have a well-developed head and many tentacles for capturing prey.

11. c. A closed circulatory system moves blood through the body in a series of closed vessels.
d. Cephalopods use jet propulsion to move at speeds of 6 m/s.
e. Mollusk fossils date to more than 500 million years ago.

12. C. Among other uses, mollusks provide food for people and other animals as well as pearls and shells for jewelry and decorations.

13. Discussion Question
What are the three common groups of mollusks?

14. Discussion Question What are the three common groups of mollusks?
 Gastropods (1 shell)
 Bivalves (2 hinged shells)
 Cephalopods (Squid, Octopus)

15. Virtual Squid Dissection

16. Section 2 – Segmented Worms
Learning Objectives
Identify the characteristics of segmented worms.
Describe the structures of an earthworm and how it takes in and digests food.
Explain the importance of segmented worms.

17. Section 2 – Segmented Worms
A. Annelids, segmented worms, have setae (bristlelike structures) to hold on to the soil and to move
They also have bilateral symmetry, a body cavity holding organs, and two body openings (mouth and anus)

18. B. Earthworms have more than 100 segments and move using their setae and two sets of muscles in the body wall.

19. 1. Earthworms ingest soil which moves to the crop for storage, then to the gizzard for grinding, then to the intestine
 wastes exit the anus and help fertilize the soil.

20. 2. Earthworms have a closed circulatory system and exchange oxygen and carbon dioxide through skin covered with watery mucus.

21. 3. Earthworms have a small brain which is connected to nerves in each segment
 they are hermaphrodites that must exchange sperm with another earthworm to reproduce.

22. C. Marine worms, or polychaetes, have segments with setae in bundles.
1. Some polychaetes are sessile, and some build tubes around their bodies for protection.
2. Some polychaetes such as the bristleworm are free-swimming.

23. D. Leeches are segmented worms without setae; they feed on blood from other animals.

24. 1. Leeches are used in medicine to prevent blood from coagulating and to heal surgical sites.
2. Leeches release chemicals that are being studied as treatments for heart and circulatory diseases, strokes, arthritis, and glaucoma.

25. E. Segmented worms are valuable since they aerate the soil, produce medically useful chemicals, and provide food for many fish, invertebrates, and mammals.

26. F. Segmented worms probably evolved in the sea and may have had a common ancestor with mollusks.

27. Discussion Question
How do earthworms breathe?

28. Discussion Question How do earthworms breathe?
 They exchange carbon dioxide and oxygen through their skin.

29. Section 3 – Arthropods Learning Objectives
Determine the characteristics that are used to classify arthropods.
Explain how the structure of the exoskeleton relates to its function.
Distinguish between complete and incomplete metamorphosis.

31. Section 3 – Arthropods A. Arthropods have:
 jointed appendages (external body parts)
 bilateral symmetry, segmented bodies
 an exoskeleton, a body cavity
 a digestive system with two openings
 a nervous system
 most species have separate sexes.

32. 1. Some arthropods have many segments, while others have fused segments forming body regions.

33. 2. A hard, thick, outer covering called an exoskeleton covers, supports, and protects the arthropod
The exoskeleton is shed and replaced occasionally in a process called molting.

34. B. Insects have three body regions

35. 1. An insect’s head has a pair of antennae, eyes, and a mouth.

36. 2. The insect’s thorax has three pairs of legs
 if the insect has wings, they are attached to the thorax

37. 3. The abdomen contains reproductive structures and an open circulatory system
 insects obtain air and release waste gases through openings called spiracles.

38. 4. Metamorphosis – series of body changes as insects become adults
a. Incomplete metamorphosis stages
 egg, nymph, adult
b. Complete metamorphosis stages
 eggs, larva, pupa, adult

40. mouth parts are diverse and adapted to diet.
5. Insects eat plants, blood from animals, nectar, decaying materials, wood, and clothes
mouth parts are diverse and adapted to diet.
Mosquitoes
Grasshoppers
Butterflies + Honeybees
Mandibles
Siphon

41. 6. Insects are successful due to their exoskeletons, ability to fly, rapid reproduction cycles, and small sizes.

42. C. Arachnids, such as spiders,ticks, and scorpions have:
 two body regions
(the cephalothorax and abdomen)
 four pairs of legs
 and no antennae

43. 1. Scorpions have a sharp, poison-filled stinger at the end of their abdomen.
 Have two well developed pincers

44. 2. Spiders inject their prey with enzymes to digest it
2. Spiders inject their prey with enzymes to digest it. (They can’t chew their food)
Oxygen and carbon dioxide are exchanged in book lungs.

45. Mites and ticks are generally parasites
ticks often carry diseases (lyme disease)
Some mites live in the follicles of human eyelashes and eyebrows.
Mites
Ticks

46. D. Centipedes and millipedes have long bodies with many segments, many legs, antennae, and simple eyes.

47. Centipedes – carnivores, one pair of legs/segment
Centipedes hunt for their prey, which includes snails, slugs, and worms.
They have a pair of venomous claws that they use to inject venom into their prey.

48. Millipedes – herbivores, two pairs of legs/segment
Millipedes feed on plants and decaying material and often are found under the damp plant material.

49. E. Crustaceans such as crabs, shrimp, and barnacles have:
 one or two pairs of antennae
 and mandibles for crushing food.

50. F. Arthropods are a food source, aid agriculture, and are an important part of ecological communities in which humans live
 Some arthropods are pests that carry disease or damage property.

51. 1. Insecticides can kill insects, but cause other environmental problems
 biological methods for controlling insects are being developed

52. 2. Some arthropod fossils are more than 500 million years old  arthropods probably evolved from a segmented worm ancestor.

53. Discussion Question
What is the exoskeleton and what is its purpose?

54. Discussion Question What is the exoskeleton and what is its purpose?
 An exoskeleton is a hard, thick, outer covering that supports and protects an arthropod.

55. Section 4 - Echinoderms Learning Objectives
List the characteristics of echinoderms.
Explain how sea stars obtain and digest food.
Discuss the importance of echinoderms.

56. Section 4 - Echinoderms A. Echinoderms have:
a hard endoskeleton covered by a thin, bumpy, or spiny epidermis
 they have radial symmetry, a mouth, stomach, and intestines (some eat plants, animals, or detritus)
 they have no head or brain, but they do have a nerve ring around the mouth

57. 1. The water-vascular system allows echinoderms to move, exchange carbon dioxide and oxygen, capture food, and release wastes.

58. 2. Echinoderms have a water-vascular system, a network of water-filled canals connected to thousands of tube feet
Tube feet hollow, thin-walled tubes that each end in a suction cup.

59. B. About 6,000 species of echinoderms exist.
1. Sea stars have at least five arms arranged around a central point
 they reproduce sexually (females release eggs and males release sperm in the water)
 can regenerate a lost arm

60. Sea Stars

62. 2. Brittle stars allow a predator to break off an arm, while the brittle star escapes
 they quickly regenerate the lost parts

63. 3. Sea urchins and sand dollars are disk- or globe-shaped animals covered with spines.
 Some sea urchins have sacs near the end of the spines that contain toxic fluid that is injected into predators.
Sand Dollars
Sea Urchins

64. 4. Sea cucumbers are soft-bodied with a leathery covering.
 They have tentacles around their mouth and rows of tube feet on their upper and lower surfaces.

65. C. Echinoderms help recycle materials and are used in research as possible medicine sources.

66. D. Echinoderms date back more than 400 million years and more closely resemble vertebrates than any other group of invertebrates.

67. Discussion Question
What physical feature is unique to echinoderms?

68. Discussion Question What physical feature is unique to echinoderms?
 The water-vascular system