Cnidarians

1. Cnidarians “The guys with the stinging tentacles”

2. All About Cnidarians

3. Evolution of multicellular animals with tissues that perform special functions • Cnidarians: Stinging animals • Mostly marine • 10,000 known species • 2 body forms: medusa and polyp

4. Anatomy A. Polymorphism- Cnidarians have more than one body form: 1. Polyp 2. Medusa

5. The life history of some cnidarians includes both polyp and medusa stages. Others spend their entire lives as either polyp or medusa

6. medusa • Free floating form which is transported by water currents, mouth with surrounding tentacles are positioned downward

7. Medusa • Umbrella shape • Tentacles around mouth • Motile, Free-swimming

8. polyp • Sessile, attached form with mouth and tentacles positioned upward

9. Polyp Form • Tube with tentacles around the mouth • Sessile Coral polyp

10. Polyp (sea anemone)

11. Polyp (Hydra)

12. Cnidarians Cnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis. • Here we also observe a large jump on the evolutionary scale: tissues that perform specific functions.

13. Animals with radial symmetry look the same from all sides and have no head, front, or back. • They do, however, have an oral surface, where the mouth is, and an aboral surface on the opposite side • See figure 7.6 page 119

15. Radial Symmetry Radial Compass jellyfish

16. tissues • Two layers present • Epidermis covers body surface (external) • Gastrodermis lines internal body cavity and is specialized for digestion • There is also a narrow, gelatinous middle layer, mesoglea,that usually doesn’t contain cells. Forms “bell” of medusae

17. Two Tissue Layers 1. EPIDERMIS – OUTER LAYER 2. GASTRODERMIS – STOMACH CAVITY MESOGLEA – JELLY MATERIAL BETWEEN TISSUE LAYERS ABUNDANT IN JELLYFISH TO HELP THEM FLOAT

18. Cnidocytes • Stinging cells • Nematocyst capsules located on tentacles • These are used for protection and feeding

19. Cnidocytes-Stinging Cells • Within the cnidocyteis the nematocyst (which is like a capsule) • The capsule has the stinging structure which is a hollow thread (Filament) with barbs • Most contain a toxin • Very small, but discharged in large numbers • Usually the sting is only strong enough to kill zooplankton or tiny fish • But there are exceptions!

21. Discharged nematocysts, • stinging cells used for defense and prey capture, have been the plague of more than fish. • Stings from certain jellyfish have resulted in death in a matter of hours, especially for infants.

22. Discharging nematocyst • http://www.youtube.com/watch?v=6zJiBc_N1Zk

23. Jellyfish stings • http://www.youtube.com/watch?v=-Tp38DUjUnM • 1:01 • http://www.youtube.com/watch?v=SP6TB8kiZB0

25. Digestive and nervous systems • Digestive system is incomplete (sac-like with mouth only) • Centrally located mouth surrounded by tentacles • Tentacles capture and handle food • Mouth opens into gut where food is digested

26. Nerve net throughout body coordinates movements • Some jellyfish also have sensory cells and contractile cells

27. One Opening System WASTES, GAMETES OUT FOOD IN Food enters through the mouth and is digested in the cells. Wastes are excreted through the mouth. Sperm and eggs are released through the mouth.

28. Response • No nervous system • No brain • Nerve net around mouth • Nerves cover the body but do not tell the difference between body parts.

29. Respiration • Via diffusion • Body is two cell layers thick

30. Habitat Aquatic: • Most are Marine • A few are freshwater

31. Feeding 1. Carnivores (predators) 2. Process of feeding a. Tentacles sting prey with nematocysts b. Tentacles grab prey c. Prey pulled into mouth 3. Prey moved into gastro-vascular cavity (GVC)* 4. GVC makes enzymes, breaks down food, extra-cellular digestion 5. Undigested food moves back out of mouth Lion’s mane eats another jelly!

32. Process of feeding 3. Prey stuffed into gastro-vascular cavity (GVC)* 4. GVC makes enzymes, extra-cellular digestion 5. Undigested food back out mouth *incomplete digestive tract (no anus)

33. Locomotion • Medusa- motile, free-swimming • Polyps- sessile,attached to hard substrate Exceptions: 1. Hydra tumbles on tentacles 2. Sea anemones glide on pedal disc

34. Reproduction 1. Asexual budding 2. Sexual a. Medusae release sperm & eggs b. Larvae are free-swimming

35. Sexual reproduction • Medusa is normally the sexual stage with epidermal gonads. Eggs and sperm released from medusa • Zygote develops into swimming larva called a planula • Planula settles on bottom to form colony • Eventually, new medusa are formed

36. Planula

37. Life Cycle of a Typical Cnidarian • Alternation of Generations • One form is the polyp (a cylinder with the closed end attached to the substrate and the open end with the mouth and tentacles directed upward) • The other form is the medusa, free-swimming, with the mouth underneath (like a jellyfish)

38. Hermaphrodite sexual Life Cycle of a Typical Cnidarian asexual Alternation of Generations

40. Cnidarian life cycle • http://www.youtube.com/watch?v=ct9KyLmnu0I • http://www.youtube.com/watch?v=K9cFbJ8qYWg

41. Phylum Cnidaria The Classes of Cnidaria are: • Anthozoa- Sea Anemones and Corals • Hydrozoa- Hydra • Scyphozoa- “true”jellyfish • Cubozoa- “box-shaped” jellyfish • Ctenophora- non stinging Cnidarians: • Comb Jellies (covering separately)

42. Class Anthozoa • All marine “flower animal” • Corals, anemones, sea fans/whips, sea pansy • Colonial polyps that normally lack a medusa stage • Sting organisms around them • Can move by crawling along the substrate • Corals secrete calcium carbonate “shells” • Most coral species possess symbiotic algae within body tissues called zooxanthellae

43. Anthozoa- sea fan

44. Anthozoa- anemone

45. Sea anemone

46. Giant Sea Anemone

47. Anthozoa- coral

48. Sun Coral

49. Brain Coral