1. End Show Slide 1 of 47 Copyright Pearson Prentice Hall Biology

2. End Show Slide 2 of 47 Copyright Pearson Prentice Hall 26-3 Cnidarians

3. End Show 26-3 Cnidarians Slide 3 of 47 Copyright Pearson Prentice Hall What is a Cnidarian? What is a cnidarian?

4. End Show 26-3 Cnidarians Slide 4 of 47 Copyright Pearson Prentice Hall What is a Cnidarian? Cnidarians are soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. They are the simplest animals to have body symmetry and specialized tissues.

5. End Show 26-3 Cnidarians Slide 5 of 47 Copyright Pearson Prentice Hall What is a Cnidarian? Cnidarians get their name from the cnidocytes, or stinging cells, located along their tentacles. Cnidarians use cnidocytes for defense and to capture prey.

6. End Show 26-3 Cnidarians Slide 6 of 47 Copyright Pearson Prentice Hall What is a Cnidarian? Within each cnidocyte is a nematocyst—a poison-filled, stinging structure that contains a tightly coiled dart. Filament Barb Nematocyte Trigger Filament

7. End Show 26-3 Cnidarians Slide 7 of 47 Copyright Pearson Prentice Hall What is a Cnidarian? When a shrimp or small fish brushes up against the tentacles, thousands of nematocysts explode, releasing enough poison to paralyze or kill the prey.

8. End Show 26-3 Cnidarians Slide 8 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians What two body plans exist in the cnidarian life cycle?

9. End Show 26-3 Cnidarians Slide 9 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Cnidarians are radially symmetrical. They have a central mouth surrounded by numerous tentacles that extend outward from the body.

10. End Show 26-3 Cnidarians Slide 10 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Cnidarians typically have a life cycle that includes two different-looking stages: a polyp and a medusa. Polyp Medusa

11. End Show 26-3 Cnidarians Slide 11 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians A polyp is a cylindrical body with armlike tentacles. In a polyp, the mouth points upward. Polyps are usually sessile. Polyp

12. End Show 26-3 Cnidarians Slide 12 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians A medusa has a motile, bell-shaped body with the mouth on the bottom. Medusa

13. End Show 26-3 Cnidarians Slide 13 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Cnidarian polyps and medusas each have a body wall that surrounds an internal space called a gastrovascular cavity. Gastrovascular cavity

14. End Show 26-3 Cnidarians Slide 14 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The gastroderm is the inner lining of the gastrovascular cavity, where digestion takes place. Gastrovascular cavity

15. End Show 26-3 Cnidarians Slide 15 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The epidermis is the outer layer of cells. Epidermis

16. End Show 26-3 Cnidarians Slide 16 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The mesoglea is a layer that lies between the epidermis and gastroderm. Mesoglea

17. End Show 26-3 Cnidarians Slide 17 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Feeding A cnidarian pulls its food through its mouth and into its gastrovascular cavity, a digestive chamber with one opening. Food enters and wastes leave the body through that same opening.

18. End Show 26-3 Cnidarians Slide 18 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The digestion that occurs in the gastrovascular cavity is extracellular, meaning that it takes place outside of cells. Partially digested food is absorbed by the gastroderm.

19. End Show 26-3 Cnidarians Slide 19 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Digestion is completed intracellularly, within cells in the gastroderm. Any materials that cannot be digested are passed out of the body through the mouth.

20. End Show 26-3 Cnidarians Slide 20 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Respiration, Circulation and Excretion Following digestion, nutrients are usually transported throughout the body by diffusion. Cnidarians respire and eliminate the wastes of cellular metabolism by diffusion through their body walls.

21. End Show 26-3 Cnidarians Slide 21 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Response Cnidarians gather information from their environment using specialized sensory cells.

22. End Show 26-3 Cnidarians Slide 22 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Both polyps and medusas have a nerve net, a loosely organized network of nerve cells. Nerve cells

23. End Show 26-3 Cnidarians Slide 23 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Cnidarians also have statocysts, which are groups of sensory cells that help determine the direction of gravity. Ocelli are eyespots made of cells that detect light.

24. End Show 26-3 Cnidarians Slide 24 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Movement Sea anemones have a hydrostatic skeleton. A hydrostatic skeleton consists of a layer of circular muscles and a layer of longitudinal muscles that, with the water in the gastrovascular cavity, enable the cnidarian to move.

25. End Show 26-3 Cnidarians Slide 25 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Reproduction Most cnidarians reproduce both sexually and asexually. Polyps can reproduce asexually by budding. In most cnidarians, sexual reproduction takes place with external fertilization. External fertilization takes place outside the female's body.

26. End Show 26-3 Cnidarians Slide 26 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians In the life cycle of Aurelia, a common jellyfish, the female releases eggs into the water, and the male releases sperm.

27. End Show 26-3 Cnidarians Slide 27 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Fertilization occurs in open water. Each zygote grows into a free-swimming larva.

28. End Show 26-3 Cnidarians Slide 28 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The larva eventually attaches to a hard surface and develops into a polyp.

29. End Show 26-3 Cnidarians Slide 29 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The polyp eventually buds and releases young medusas that begin the cycle again.

30. End Show 26-3 Cnidarians Slide 30 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians What are the three groups of cnidarians?

31. End Show 26-3 Cnidarians Slide 31 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Cnidarians include: jellyfishes hydras and their relatives sea anemones and corals

32. End Show 26-3 Cnidarians Slide 32 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Jellyfishes The class Scyphozoa contains the jellyfishes. Jellyfishes live their lives primarily as medusas. The polyp form of jellyfishes is restricted to a small larval stage, and no elaborate colonies ever form. Jellyfishes reproduce sexually.

33. End Show 26-3 Cnidarians Slide 33 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Hydras and Their Relatives The class Hydrozoa contains hydras and related animals. The polyps of most hydrozoans grow in branching colonies that can extend more than a meter. Within the colony, polyps are specialized to perform different functions.

34. End Show 26-3 Cnidarians Slide 34 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians The most common freshwater hydrozoans are hydras. Hydras differ from other cnidarians in this class because they lack a medusa stage. Instead, they live only as solitary polyps. Hydras reproduce asexually, by budding, or sexually, by producing eggs and sperm in the body wall.

35. End Show 26-3 Cnidarians Slide 35 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Sea Anemones and Corals The class Anthozoa contains sea anemones and corals, animals that have only the polyp stage in their life cycle. Anthozoans all have a central body surrounded by tentacles.

36. End Show 26-3 Cnidarians Slide 36 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Many species are colonial, or composed of many individual polyps. Sea anemones are solitary polyps that live at all depths of the ocean.

37. End Show 26-3 Cnidarians Slide 37 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Most corals are colonial, and their polyps grow together in large numbers. New polyps are produced by budding, and as the colonies grow, they secrete an underlying skeleton of calcium carbonate, or limestone.

38. End Show 26-3 Cnidarians Slide 38 of 47 Copyright Pearson Prentice Hall Ecology of Corals Worldwide distribution of corals is determined by a few variables: temperature water depth light intensity

39. End Show 26-3 Cnidarians Slide 39 of 47 Copyright Pearson Prentice Hall Ecology of Corals The corals that build coral reefs require high levels of light—these corals rely on algae that capture solar energy, recycle nutrients, and help corals lay down their calcium carbonate skeletons.

40. End Show 26-3 Cnidarians Slide 40 of 47 Copyright Pearson Prentice Hall Ecology of Corals Symbionts provide as much as 60 percent of the energy corals need. This allows coral reefs to live in water that carries few nutrients.

41. End Show 26-3 Cnidarians Slide 41 of 47 Copyright Pearson Prentice Hall Ecology of Corals Many coral reefs suffer from human activity: Silt and sediments from logging, farming, mining, and construction smother corals. Chemical fertilizers, insecticides, and industrial pollutants poison corals. Overfishing upsets ecological balance. Stresses that makes coral reefs susceptible to other threats.

42. End Show - or - Continue to: Click to Launch: Slide 42 of 47 Copyright Pearson Prentice Hall 26-3

43. End Show Slide 43 of 47 Copyright Pearson Prentice Hall 26-3 The characteristic that defines the cnidarians is a.bilateral symmetry. b.stinging cells. c.a gastrovascular cavity. d.cephalization.

44. End Show Slide 44 of 47 Copyright Pearson Prentice Hall 26-3 Which of the following statements is generally true of polyps and medusas? a.Polyps are sessile, and medusas are motile. b.Polyps are motile, and medusas are sessile c.Both polyps and medusas are sessile. d.Both polyps and medusas are motile.

45. End Show Slide 45 of 47 Copyright Pearson Prentice Hall 26-3 During the life cycle of Aurelia, the zygote grows into a free-swimming a.polyp. b.larva. c.medusa. d.gemmule.

46. End Show Slide 46 of 47 Copyright Pearson Prentice Hall 26-3 Cnidarians, such as the sea anemone, move using a.water currents. b.an exoskeleton. c.a hydrostatic skeleton. d.an endoskeleton.

47. End Show Slide 47 of 47 Copyright Pearson Prentice Hall 26-3 Groups of sensory cells that help cnidarians determine the direction of gravity are known as a.nerve nets. b.statocysts. c.ocelli. d.cnidocytes.

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