Phylum Cnidaria

The following questions will help you to review the material from the lecture as well as the text. I have included suggested reading material in case you would like to follow up on any of the aspects covered in this section.

1. How does the phylum Cnidaria differ from the phylum Porifera?
2. Can one push a medusa through a mesh and expect that the organism will reform? Why or why not?
3. Do cnidarians have radial or bilateral symmetry? Explain.
4. As one touches a sea anemone it slowly recoils away from your hand. From this simple observation one can conclude that the anemone has two very important characteristics. These features have remained in all animals that later evolved on the planet. What are the two characteristics and what are the implications for animal evolution?
5. Describe the structure of a typical polyp and a medusa. Mention important structures and cell layers as well as their function.
6. Why do polyps and medusas look so similar?
7. What is the mesoglea?
8. How do cnidarians digest food items? How do they get rid of any unwanted remains?
9. What is a cnidocyte? A nemotocyst? What is their function? Are there different kinds of nematocysts? Why?
10. Briefly discuss the evolutionary consequences of the specialized cell types that exist within the phylum.
11. What is a nerve net? Function? Evolutionary consequences?
12. Describe a cross section of a typical polyp such as Hydra. What kind of structures would be visible?
13. How do cnidarians access oxygen and get rid of carbon dioxide (both of which are crucial to maintain cellular respiration within the cells)?
14. Briefly describe the taxonomy of the phylum Cnidaria with a focus on the different classes.
15. A common asexual process within the phylum is the process of budding. Explain the process.
16. Describe the life cycle of Aurelia (moon jellies).
17. How does the life cycle of Aurelia allow for movement of the organism?
18. Explain the following terms: planula, strobila, ephyra, medusa, scyphistosoma, rhopalia.
19. The medusae are part of the plankton (what is the definition of plankton). However, many medusas spend considerable energy contracting in a pulsating fashion. This seems to be a waste of energy considering that these animals are "drifters". What is a current hypothesis in regards to why these animals have a pulsating movement (hint: the answer was in the film you watched).
20. What is a colonial polyp? How do they differ from regular polyps? Use Obelia  to explain the structure/function of this organism as well as its life cycle.
21. What is a gastrozooid? A gonozooid? A stolon?
22. The Portuguese man-of-war is an unusual example of a cnidarian. Explain.
23. What are corals?
24. Many cnidarians have symbiotic relationships. The corals in particular are involved in a mutualistic relationship with algae. Discuss the relationship and its importance.
25. Is it appropriate to refer to coral reefs as the tropical forests of the marine realm? Explain.
26. Where do you find coral reefs across the world? Give four different examples.
27. What proportion of the earth's surface is taken up by coral reefs?
28. How many of the world's described marine species can be found on the coral reefs of the world?
29. How does the primary productivity of coral reefs compare to other terrestrial and aquatic biomes?
30. Can you find corals anywhere or are they restricted to certain marine areas?
31. "Corals are always polyps"! Explain the statement.
32. "Polyps feed on zooplankton". True or false? Explain.
33. Do the polyps exhibit any feeding patterns linked to the time of the day? Explain.
34. Do coral reefs have a "skeleton"? Explain.
35. Describe the structural relationship between animals and "skeleton". How do coral reefs form?
36. Are the polyps connected?
37. What is the role of zooxanthellae in the formation of coral reefs?
38. Describe the symbiotic relationship between the polyps and zooxanthellae in detail. How do the different partners benefit from the interaction?
39. Is this an important interaction from a biological perspective? Why or why not?
40. Corals within the reefs have interesting shapes. Describe and explain their shapes.
41. Why are coral reefs so important from a biologist's perspective?

• Gould: "Wonderful Life - The Burgess Shale and the Nature of History" - Gould explores early animal evolution. A very interesting and thought provoking book.
• Burnett: "The Shape of Life" - An introduction to the body plans of animals. Informative with great photos. Accompanies the PBS series.
• Connor: "Jellies - Living Art" - An introductory book on jellies focusing on imagery.
• Brusca/Brusca: "Invertebrates" - Major (and expensive) reference book on invertebrates. Good chapter on Cnidarians. Find it in a library.
• Pearse/Buchsbaum: "Animals without Backbones" - Great introductory resource on invertebrates.
• Conniff: "Spineless Wonders" - Not linked to Cnidarians. A great and fun collection of essays about invertebrates. Entertaining.

Page created by: Peter Svensson Updated: October  2015