1. Phylum Cnidaria

4. Phylum Cnidaria Radial symmetry
Mouth at oral end surrounded by tentacles.
One opening into and out of gastrovascular cavity.
Cnidocytes that discharge pneumatocysts
Two body forms
Polyp
Medusa
Two germ layers
Nerve net

5. Radial symmetry

6. Mouth and Tentacles

7. Cnidarians are the oldest existing animals that have specialized tissues.
Cnidarians have two body forms.
polyps
In the polyp form
of a coral, the tentacles
and mouth face upward.

8. medusas
In the medusa form of a jellyfish, the tentacles and
mouth face downward.

9. The four major cnidarian classes are defined by their dominant body form.
Anthozoans such as sea anemones have a dominant polyp stage.

10. The four major cnidarian classes are defined by their dominant body form.
Hydrozoans such as hydra alternate between forms.

11. The four major cnidarian classes are defined by their dominant body form.
Scyphozoans are jellyfish with a dominant medusa form.

12. The four major cnidarian classes are defined by their dominant body form.
Cubozoans such as sea wasps have a dominant medusa form.

13. Fig. 13.2
Fig. 13.2

14. Generalized Cnidarian Life Cycle
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Generalized Cnidarian Life Cycle

15. Cnidocyte Structure and Nematocyst Discharge
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Cnidocyte Structure and Nematocyst Discharge

16. Cnidarians are made up of two tissue layers separated by mesoglea.
gastrovascular cavity
mouth
mesoglea
tentacle
oral arms
The outer tissue layer has three cell types.
contracting cells
nerve cells
cnidocytes (which contain nematocysts)
barbs
coiled
nematocyst
discharged

17. Nervous System
Nerve cells, arranged in a nerve net.

18. Class Hydrozoa Freshwater & marine.
Cnidocytes present only on epidermis.
Medusa (if present) with a muscular velum.
Mesoglea without ameboid cells.
Asexual reproduction by budding.
Sexual reproduction via gametes produced by epidermis & released into water.

19. Class Hydrozoa
Hydra
Obelia
Gonionemus
Physalia

20. Class Hydrozoa Hydra Encapsulated embryo Ovaries Budding Spermaries
Sexual cycle
Asexual cycle

21. Hydra
Body Wall
Gastrovascular
cavity
Gastrodermis
Mesoglea
Epidermis

22. Fig. 13.9

23. Obelia

24. Obelia
Gonangium
Medusae
Medusa bud

25. Class Hydrozoa Gonionemus
Fig b

26. Class Hydrozoa Gonionemus
Velum

27. Class Hydrozoa Physalia

28. Class Scyphozoa Tentacles up to 70 meters in length
Cnidocytes present in gastrodermis & epidermis
Thick mesoglea contains ameboid cells
Gametes produced by gastrodermis
All marine

29. Class Scyphozoa Aurelia

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Aurelia Life History

31. Fig
Fig

32. Planula Larva
Ciliated larva that can swim to a new location

33. Aurelia
Mesoglea
Eggs
Gastrovascular
cavity
Mouth

34. Aurelia
Oral arm
Gastric pouch
Mouth
Tentacles

35. Class Cubozoa Medusa dominant & cuboid
Tentacles arise at four corners from blade-like pendalium.
All marine
Strong swimmers which prey primarily on fish
Stings of some may be fatal within minutes to humans.

36. Class Cubozoa
Gonad
Pedalium
Tentacle

37. Class Cubozoa Chironex Sea Wasp

38. Class Anthozoa Medusa stage absent Solitary or colonial
Some produce protective skeletons
Gastrovascular cavity subdivided by at least 8 mesenteries
Cnidocytes on mesenteries
Mesoglea contains ameboid cells
All Marine

39. Class Anthozoa Sea Anemone

40. Class Anthrozoa Metridium
Tentacles
Mouth
Pharynx
Septum
Gastrovascular cavity

41. Symbiosis

42. Sea Anenome Feeding

43. Class Anthozoa Corals Protective skeleton of calcium carbonate
Polyp retracts when not feeding

44. Zooxanthellae Photosynthetic dinoflagellates (brown) Live in corals
Provide nutrients for coral by photosynthesis
Mutualism

45. Corals Colony of interconnected polyps

46. Class Anothozoa Meandrina Brain Coral

47. Class Anothozoa Gorgonia Sea Fan

48. Class Anothozoa Tubipora Pipe Organ Coral

49. Class Anothozoa Actinodiscus Mushroom Coral

50. Class Anothozoa Acropora Staghorn Coral

51. Coral Reefs
Formed over thousands of years from successive layers of coral skeleton deposits (calcium carbonate forms underwater mountains of coral animal skeletons)
The underwater equivalent of the amazon jungle- very high species diversity and biomass
Reefs contain sponges, colonial hydrozoans, anemones, many varieties of coral, fish, many types of worms we’ve not discussed, not to mention bryozoans, ctenophores, protists, bacteria, etc etc..

52. Copyright © The McGraw-Hill Companies, Inc
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Coral Reef Ecosystem
Photo © McGraw-Hill Higher Education, Barry Barker, Photographer

53. Cladogram of Cnidaria Anthozoa Scyphozoa Cubozoa Medusa cuboidal
Loss of medusa
Hydrozoa
Polyp stage reduced
Septa divide gastrovascular cavity
Radial symmetry, cnidocytes, planula larva

54. The End