2. Most asteroids are carnivores. How do you think they catch and deal with their prey? What adaptations make seastars good predators?

3. Look carefully at the fossil ophiuroids to convince yourself that these are indeed brittle stars.

4. Examining a recent brittle star, locate the following: central disc, oral and aboral surfaces, podia, mouth, bursal slits. Sketch.

5. How do ophiuroids differ from asteroids? What do these differences mean in terms of their lifestyles?

6. Looking at the recently expired sea urchins, you should be able to find: oral and aboral surfaces, spines, podia, mouth, anus, madreporite, ambulacra and interambulacra.

7. What is the structure that has been removed (and retained for your perusal) from the urchins? Where was it located when the animal was alive, and what was its function?

8. Looking at the pieces of urchin test, what is the function of the small paired holes? What are the bumps on the surface?

9. Now that you've had a chance to look at both seastars and sea urchins, why do you think that fossil seastars might be less common than fossil sea urchins?

10. Locate "anterior", "posterior", ambulacral and interambulacral areas, axis of bilateral symmetry. Why do you think these echinoids have bilateral symmetry?

11. What features do these fossil irregular echinoids share with regular echinoids? Provided the preservation was good enough, what would tell you that these are irregular echinoids?

12. Looking at the broken sand dollar test, what function do you think the internal struts perform?

13. Notice the many fine spines on these recent sand dollars. Why are their spines different from those of regular urchins? What function do you think the spines perform?

14. Edrioasteroids and helicoplacoids are examples of echinoderm evolutionary experiments. What do you think these critters did for a living?

15. Examine these fossil crinoid calyxes. The calyx is generally not fossilized, because the plates composing it usually disarticulate soon after the animal dies. Sketch a typical crinoid, labeling calyx, stalk, arms and pinnules.

16. Examine the examples of cystoids and blastoids. Cystoids attached themselves to the substrate either directly or on a stalk (like most crinoids). Their calyxes are composed of numerous irregularly arranged plates. The blastoids are another group of stalkd echinoderms. Pentremites is one of the most characteristic fossils of this extinct class. Sketch these specimens, labeling ambulacrum, ambulacral groove, spiracles, mouth and anus.

17. Crinoids, cystoids and blastoids are all assigned to the Pelmatozoa. Compare and contrast these three groups with regard to feeding, respiration and calical plate organization.

Back to Chapter Thirteen.