Cnidarians

1. Cnidarians

2. What is a cnidarian? • invertebrates • more than 9000 species • jellyfishes, corals, sea anemones, and hydras. • worldwide • all but a few cnidarians are marine

3. What are cnidarians? • variety of colors, shapes and sizes • - can be as small as the tip of a pencil. • two distinct body forms during their life cycles Medusa Polyp

4. What are cnidarians? • polyp =sessile form of a cnidarian. Its mouth is surrounded by tentacles. - sea anemones, corals, and hydras. • medusa = free-swimming form of a cnidarian. • - jellyfish

5. Body Form Tentacles The Medusa It possesses an umbrella-shaped, floating body, called a bell, with the mouth on its underside.

6. Body Form mouth The Polyp Attached to substrate, the mouth is on the top surrounded by tentacles.

7. Body form In cnidarians, one body form may be more observable than the other. In jellyfishes, the medusa is the body form usually observed. http://www.masla.com/invert/moon-jellyfish.html The polyp is the familiar body form of hydras. http://www.microscope-microscope.org/gallery/Mark-Simmons/pages/hydra2.htm

8. Body structure Mouth Tentacle • radially symmetrical • one body opening • two cell layers • How is this similar to sponges? Cavity Inner cell layer Jellylike layer Bud Outer cell layer Disc

9. Body structure Mouth • cell layers are organized into tissues with specific functions. Tentacle Cavity Inner cell layer - inner layer mainly assists in digestion It surrounds the GASTROVASCULAR CAVITY Jellylike layer Bud Outer cell layer Disc

10. Body structure • two cells layers allows easy diffusion of: - Oxygen dissolved in water, it can diffuse directly into body cells. - Carbon dioxide /other wastes moves out of the body cells directly into the surrounding water.

11. Body form Most cnidarians undergo a change in body form during their life cycles. Medusa Polyp At some point, most Cnidarians exist as both a polyp and a medusa.

12. Reproduction in cnidarians • sexual and asexual reproduction - Sexual reproduction occurs in only one phase of the life cycle – the Medusa IF there is no medusa stage, then the polyp can reproduce sexually.

13. Sexual Reproduction in Cnidarians Female Male Eggs Both the medusae and polyps are diploid animals. Fertilization Asexual Reproduction Blastula Bud Larva Polyp

14. Digestion in cnidarians • predators • - capture or poison prey using nematocysts A nematocyst is a capsule that contains a coiled, threadlike tube. The tube may be sticky or barbed, and it may contain toxic substances. Nematocysts are located in stinging cells that are on tentacles.

15. Digestion in cnidarians Nematocyst before discharge Nematocyst after discharge

16. Digestion in cnidarians Once captured by nematocysts, prey is brought to the mouth by contraction of the tentacles. Mouth Gastrovascular cavity Polyp Mouth Medusa

17. Digestion in cnidarians • Food enters gastrovascular cavity • digestive cells release enzymes to break down prey • undigested materials are ejected back out through the mouth.

18. Diversity of Cnidarians There are four classes of cnidarians: • Hydrozoa • Scyphozoa • Cubozoa • Anthozoa

19. Hydrozoa • two groups • - hydroids (hydra) • - siphonophores (Portuguese man-of-war) • marine animals • branching polyp colonies formed by budding • found attached to pilings, shells, and other surfaces.

20. Hydrozoa The siphonophores are floating colonies that drift about on the ocean’s surface. The Portuguese man-of-war, Physalia, is an example of a siphonophore hydrozoan colony. Each individual in a Physalia colony has a function that helps the entire organism survive.

21. Anthozoa • exhibit only the polyp form. • Corals • Sea anemones • Sea fans

22. Corals • live in colonies of polyps in warm ocean waters around the world. • secrete protective, cuplike calcium carbonate shelters around their soft bodies. Colonies of many coral species build the beautiful coral reefs that provide food and shelter for many other marine species.

23. Corals Corals that form reefs are known as hard corals. • soft corals do not build calcium carbonate structures – not reef builders.

24. Corals The living portion of a coral reef is a thin, fragile layer that grows on top of the shelters left behind by previous generations. Although corals are often found in relatively shallow, nutrient-poor waters, they thrive because of their symbiotic relationship with microscopic, photosynthetic protists called zooxanthellae.

25. Corals The zooxanthellae produce oxygen and food that the corals use, while using carbon dioxide and waste materials produced by the corals. These protists are primarily responsible for the bright colors found in coral reefs.

26. Corals Because the zooxanthellae are free-swimming, they sometimes leave the corals. Corals without these protists often die.

27. Corals and Global Warming • Corals are being threatened by rising ocean temperatures and increasing acidity • Increasing temperatures stress the zooxanthellae and they leave the corals – this results in coral bleaching

28. Corals and Global Warming • Without the colorful zooxanthellae, the corals appear white. • Coral bleaching is reversible, but often does not happen. • At current rate, 70% of coral reefs will be bleached in the next 20-30 years. • At present 35 million acres of reef have been destroyed.

31. http://www.wri.org/map/coral-reefs-world-classified-potential-threat-human-activitieshttp://www.wri.org/map/coral-reefs-world-classified-potential-threat-human-activities

32. Corals and Global Warming • Corals provide habitat for 25% of marine fish • About 1 billion people rely on fish as their primary food source

33. Corals and Global Warming • Tourism – over a billion dollars is spent every year in the Caribbean, Australia (3.9 billion/year), and the Pacific Islands • 1.2 Billion in Florida each year

34. Corals and Global Warming • Corals are used for pharmaceuticals • Chemical extracts from corals have helped create drugs to treat AIDS, Cancer, Arthritis, Inflammatory disorders, and pain killers • They are beneficial for patients with heart, kidney, and liver transplants.

35. Corals and Global Warming • Coral Reefs are beautiful! • Most diverse ecosystem – “Ocean Rainforest” • 4000 species of fish, 800 species of coral

36. Scyphozoa The fragile and sometimes luminescent bodies of jellyfishes can be beautiful. Some jellyfishes are transparent, but others are pink, blue, or orange. The medusa form is the dominant stage in this class.

37. Scyphozoa • musclelike cells in their outer cell layer that can contract. • When these cells contract together, the bell contracts, which propels the animal through the water.

38. Cubozoa • Until recently, box jellyfish were included in Class Scyphozoa. • They differ from Scyphozoans in several ways

39. Cubozoa • Their bells are square-shaped, instead of round • They have primitive brains • They have eyes • They swim, not float • They sleep

40. Cubozoa • The Irukandji in Australia is one of the most dangerous animals • It is very small, only 2.5 cm from bell to tentacles

41. Giant Jellyfish • While Irukandji is very small, Japan has been invaded by Nomura’s jellyfish – the giant jellyfish.

42. Research: • What are Nomura’s Jellyfish? • Where are they found? Just Japan? • What causes them to get so big? • Are they dangerous? • Are they new? Or are they only now getting noticed?

43. Giant Jellyfish • 6.5 ft wide and 450 lbs • More common in China and Korea • Only recently in Japan

44. Giant Jellyfish • Not much is known, Japan studying mating/migration habits • Choking fishing nets • Possible warmer seas (global warming) causes increase in population • http://video.google.com/videoplay?docid=2208948115892996006&q=giant+jellyfish&total=103&start=0&num=10&so=0&type=search&plindex=0

45. Where did they come from? The earliest known cnidarians also date to the Precambrian, about 630 million years ago. The earliest coral species were not reef builders, so reefs cannot be used to date early cnidarians. The larval form of cnidarians resembles protists, and because of this, scientists consider cnidarians to have evolved from protists.