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? 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.

4. End Show 26-3 Cnidarians Slide 4 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.

5. End Show 26-3 Cnidarians Slide 5 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

6. End Show 26-3 Cnidarians Slide 6 of 47 Copyright Pearson Prentice Hall What is a Cnidarian?

7. End Show 26-3 Cnidarians Slide 7 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Cnidarians are radially symmetrical. Cnidarians typically have a life cycle that includes two different-looking stages: a polyp and a medusa.

8. End Show 26-3 Cnidarians Slide 8 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

9. End Show 26-3 Cnidarians Slide 9 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

10. End Show 26-3 Cnidarians Slide 10 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

11. End Show 26-3 Cnidarians Slide 11 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

12. End Show 26-3 Cnidarians Slide 12 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.

13. End Show 26-3 Cnidarians Slide 13 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.

14. End Show 26-3 Cnidarians Slide 14 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians Fertilization occurs in open water. Each zygote grows into a free-swimming larva.

15. End Show 26-3 Cnidarians Slide 15 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The larva eventually attaches to a hard surface and develops into a polyp.

16. End Show 26-3 Cnidarians Slide 16 of 47 Copyright Pearson Prentice Hall Form and Function in Cnidarians The polyp eventually buds and releases young medusas that begin the cycle again.

17. End Show 26-3 Cnidarians Slide 17 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Cnidarians include: jellyfishes hydras and their relatives sea anemones and corals

18. End Show 26-3 Cnidarians Slide 18 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Jellyfishes The class Scyphozoa contains the jellyfishes. Jellyfishes live their lives primarily as medusas.

19. End Show 26-3 Cnidarians Slide 19 of 47 Copyright Pearson Prentice Hall Groups of Cnidarians Hydras and Their Relatives The class Hydrozoa contains hydras and related animals. Hydras differ from other cnidarians in this class because they lack a medusa stage. Instead, they live only as solitary polyps.

20. End Show 26-3 Cnidarians Slide 20 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.

21. End Show 26-3 Cnidarians Slide 21 of 47 Copyright Pearson Prentice Hall Ecology of Corals Worldwide distribution of corals is determined by a few variables: temperature water depth light intensity

22. End Show - or - Continue to: Click to Launch: Slide 22 of 47 Copyright Pearson Prentice Hall 26-3

23. End Show Slide 23 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.

24. End Show Slide 24 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.

25. End Show Slide 25 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.

26. End Show Slide 26 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.

27. End Show Slide 27 of 47 Copyright Pearson Prentice Hall 26-3 The stinging cells found in all Cnidarians are called a.choanocytes. b.cnidocytes. c.polyps. d.medusas.

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