Part C

Observing the Anatomy of a Sea Urchin

18. Using forceps, hold a preserved sea urchin under running water to remove excess preservative. Then, place the sea star in a dissection tray. What evidence can you find that indicates that the sea urchin has penta-radial symmetry?

19. Observe the sea urchin's spines. Answer the same questions for the sea urchin's spines that you answered for the sea star's spines in step 5.

20. Examine the sea urchin's oral surface. Find the mouth, and use a sharp probe to explore the structures around the mouth. How does the sea urchin's mouth differ from the sea star's?

21. Examine the sea urchin test. What might be the function of the rows of small pores on the test? What might be the function of the small bumps on the test?

22. Jjt^ A- Dispose of the specimens according to the directions from your teacher. Then, clean up your materials, and wash your hands before leaving the lab.

Analysis and Conclusions

1. Which features are shared by sea stars and sea urchins?

2. What are some of the structural differences between sea stars and sea urchins?

Further Inquiry

Observe how living sea stars move in a saltwater aquarium. Add some live mussels, and observe the feeding behavior of the sea stars.

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