Amazing World of Cnidarians: Jellyfish, Coral, and More

1. Phylum Cnidaria

2. Cnidarians  -  jellyfish, coral, hydra, sea anemone *Named after the stinging cells found on their tentacles called CNIDOCYTES

3. Cnidarians • Are soft bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. • The simplest animals to have body symmetry and specialized tissues.

4. General Characteristics • About 9000 species • Simple nervous system • Diploblastic organization • Endoderm • Ectoderm

5. Most Cnidarians have radial symmetry

6. General Characteristics Cont’d- • Either tubular/vase or bell/cup shaped • Only animal with cnidocytes • Cnidocytes-specialized stinging cells (on tentacle) • All marine (aquatic)

7. Cnidarians have two body forms: polyp (vase shaped)               medusa (cup shaped)

8. Body Plan • Cnidarians’ bodies are organized around the gastrovascular cavity, where digestion takes place • GV has a single opening that serves as both mouth and anus

9. Body Plan • Cnidarians typically have a life cycle that includes two different looking stages: a polyp and a medusa. • Polyp: a cylindrical body with arm like tentacles • Medusa: a motile, bell-shaped body with the mouth on the bottom.

10. 2 Layers of Cells • Diploblastic: • Gastrodermis: lines GV cavity • Epidermis: lines the outside of the body (the skin)

12. Cnidarian Body Wall

13. Stinging Cells • Have Cnidocytes • Contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and inject a toxin or entangle prey

14. Cnidocyte

16. Feeding • Gastrovascular cavity- a digestive chamber with one opening • Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

17. Feeding Cont.

18. Nervous and Movement • sensory receptors • Both polyp and medusa have a nerve net • A loosely organized network of nerve cells that together allow cnidarians to detect stimuli • Muscles help in directional movement & capturing prey

19. Life Cycles • Cnidarians have two body forms that are representative of the sexual and asexual life cycles that they undergo. • Polyp • Medusa

20. Polyp • Usually attaches to a substrate at the aboral end • Oral end is surrounded by feeding tentacles

21. Medusa • Sexual • Shaped like an upside-down bowl • Tentacles surround the mouth that is housed underneath the bell

22. Respiration, Excretion and circulation • Following digestion, nutrients are usually transported throughout the body by diffusion. • They respire and eliminate the wastes of cellular metabolism by diffusion through their body cells.

23. Reproduction • Both sexual and asexual • Sexual • Gametes released into water • Fertilization takes place to create free-swimming planula • Asexual • By budding

24. Generalized Cnidarian Life Cycle

26. Examples • Scyphozoa: Jellyfish • Anthozoa: Sea anemones & Corals • Hydrozoa: Hydra • Cubozoa: Box Jellies

27. Class Hydrozoa • Ex. Hydras

28. What kind of symmetry does hydra have? Is it a medusa or a polyp? The Hydra is a freshwater cnidarian

29. Video of hydra at http://www.microscopyu.com/moviegallery/pondscum/hydra/

31. Includes hydras, fire corals, and Portuguese Man of War • Display alternation of generations • Polyp • Medusa

32. Portuguese Man of War - cnidarian that floats in the water and has long tentacles

33. Class Scyphozoa • True Jellyfish • Small polyp stage during life cycle

35. Class Anthozoa • Polyps that are flower-like • Includes sea anemones, corals, sea whips, and sea fans

37. Coral Reefs are made from the skeletons of cnidarians

38. Coral Characteristics • One of the most biologically diverse places in the world!

39. Coral characteristics • Types of Corals: • Hermatypic – reef forming corals, have zooxanthallae, found in warm, shallow waters

40. Coral Characteristics • Zooxanthallae (type of Protist) form a symbiotic relationship with coral • Zooxanthallae gives coral its color • Coral polyps provide shelter • Zooxanthallae

41. Coral Characteristics • Two main types of corals (con’t) • Ahermatypic – non-reef forming, grow in deep water, are found in polar to tropical waters

42. Coral Characteristics • Coral reproduction • Most are monoecious (hermaphroditic) • External fertilization- release sperm and eggs into the water • Many reproduce by budding as well (forms coral reefs)

43. Reef Structure • Anatomy of a coral polyp

44. Reef Problems • Disease • Warming water temps – may be the cause of coral “bleaching” • Increasing sediments • Human footprints

47. Multimedia Sponge Images and Videos - http://www.junglewalk.com/video/Sponge-movie.htm Cnidarian Images and Videos - http://www.junglewalk.com/video/Coelantrate-movie.htm General Invertebrate Movies at National Geographic --- really good video on the portuguese man of war (under invertebrates) Hydra Video at  http://www.schooltube.com/video/55045/Hydra