Phylum Cnidaria

1. Phylum Cnidaria Jellyfish, Coral, Sea Anemone, and Hydroids

2. Cnidarians • Stinging cell animals • Also Known As: Coelenterates: “Hollow Gut” • RadialSymmetry: similar body parts surrounding a central axis

3. Body Plan • No segments: oral and aboral sides • HydrostaticSkeleton: fill body cavity with water to remain upright. • Shrink down as defense • Organized at tissue level. (No true organs) • Epidermis: outer cells (ectoderm) • Gastrodermis: lines stomach (endoderm) • Mesoglea: middle layer of gelatinous material; can be thick or thin.

5. Digestion • Food is digested in the sac-like digestive cavity (only one opening) • Extracellular and intracellular digestion • Extracellular: outside of cells • Intracellular: inside of cells • Waste is expelled out of the mouth

6. Unique Features • Cnidoblasts: stinging cells • Inside each cell is a nematocyst, coiled thread with barb at the end. • The nematocyst can be discharged by either physical or chemical stimulus. • Physical- cnidocil (modified flagella) acts as a trigger • Contain a poisonous neurotoxin, varies by species

8. Cnidoblast

9. Nematocyst

10. Nervous System • Nerve cells interconnect to form a nerve net

11. Life Cycle • Jellyfish have separate sexes • Both sexual and asexual reproduction • Sexual: external or internal (depending on species), sperm and egg form a zygote which grows into a swimming larva called the planula. • In some cases the planula attaches to a hard substrate and develops into a polyp.

12. Life Cycle cont. • The polyp resembles an upside-down jellyfish medusa. • Small umbrella like medusas break off from the polyp by budding (asexual)

14. Classification of Cnidarians • Class Hydrozoa- Hydra, Physalia, and Obelia • Class Scyphozoa- True Jellyfish • Class Cubozoa- box jellyfish • Class Anthozoa- Corals and Sea Anemones

15. Class Hydrozoa • Usually colonial, except Hydra • Composition of colonies- 3 types 1. Gastrozoid- responsible for feeding 2. Gonozoids- responsible for sexual reproduction 3. Dactyliozoids- responsible for defense; have numerous nematocysts.

19. Class Scyphozoa • All marine; medusa is dominant life cycle • Mesoglea is a large part of the body (mostly dead matter) • Gastroderm have nematocysts; food may be eaten alive • More toxic than hydrozoans • Well developed sensory organs and glands - eyespot and chemoreceptors

24. Class Cubozoa • Cube-like jellyfish • Have four flattened, blade-like structures called pedalia • Complex eyes with lenses and retinas (no brain though) • Only 16 species: Irukandji and Chironex- deadly box jellyfish. Can kill a human in minutes.

25. Irukandji: Carukia barnes • One of, if not the deadliest box jellfish. • 2.5 cm (1 inch) in diameter

26. Box Jellyfish Sting

28. Chironex- Sea Wasp

31. Class Anthozoa • No medusa stage in life cycle • Polyps produce eggs and sperm that develop into planula larva • Solitary: sea anemone • Colonial: coral

32. Tube Sea Anemone

33. Sea Anemone

35. Soft Coral

36. Corals and Coral Reefs • Corals are colonial cnidarians • Dominant form is the polyp • Coral reef is a massive structure composed of calcium carbonate built by coral polyps and the organisms that live with in them • The polyps take up calcium in the sea water and zooxanthellae, which live inside the polyp, take up CO2, which make limestone

37. Zooxanthellae

38. Hard Coral

39. Coral Reefs • Found only in tropical areas • Warm and clear water • Shallow water- zooxanthellae require sunlight to photosynthesize • Zooxanthellae are the primary producers of the coral reef

40. Coral Reef Formation • Fringing Reef: occurs when a seamount pierces the sea surface to form an island and provides a base on which the coral can grow • Barrier Reef: occurs if a seamount subsides slowly enough and the coral continues to grow upward at a rate that is not exceeded by the rising water. A lagoon is formed. • Atoll- occurs if the seamount disappears below the surface and the coral reef is left as a ring.

43. Atafu Atoll: South Pacific

44. Symbiosis and Cnidarians • Symbiosis: literally means to live together • Mutualism: both organisms benefit from living together • Commensalism: one organism benefits, the other is unaffected • Parasitism: one organism benefits, one is harmed.

45. Clownfish and Anemones

46. Sea Anemones and Clownfish • Usually, fish the size of clownfish are stung and eaten by an anemone • Clownfish become immune to the anemones nematocysts because of a mucus coating • The mucus inhibits the anemone’s sting • The anemone provides protection and scraps of food for the clownfish • The clownfish lures prey into the anemone and cleans the anemone • What kind of relationship is this?______________

47. Coral and Zooxanthellae

48. Corals and Zooxanthellae • Zooxanthellae are dinoflagellates that are taken up by the coral polyps. • Zooxanthellae contain chloroplasts • Coral use the glucose made by the zooxanthellae as an energy supplement • The zooxanthellae benefit because they are protected and receive nutrients from the coral polyp. • What type of relationship is this? _____________

49. Phylum Ctenophora Comb Jellies Take notes on your own sheet of paper, only write down what is underlined.

50. Ctenophora