Echinoderm survey:
Starfish and sea cucumbers are only two of common groups of echinoderms.
We also have some brittlestars and sea urchins for you to view.
One of unique structures found on some echinoderms are pedicellaria. Unfortunately the starfish we have available do not have pedicellaria. However almost all sea urchins do, so use the few specimens we have to view these interesting organs.
Exercise one: Sea urchins and Pedicellaria
Pedicellaria in the sea urchin are found on the apical surface. We have a pencil urchin and two tuxedo urchins. To locate pedicellaria on the tuxedo urchin focus on what appears to be smooth area between the spines. Those looking for pedicellaria on the pencil urchin deserve extra credit. Be sure to call the rest of the class over when you find them so they can also observe their location. Can you or others in the class try to speculate on why they are found in this location on pencil urchins?
Obtain a short film of pedicellaria movement in tuxedo urchins or an photograph of pedicellaria in the pencil urchins. Compare the spine found on the sea urchins and starfish in your journal. Are the spines for example, more motile in the sea urchin?
Exercise two: Sea urchins and Aristotle’s lantern,
Before returning your specimen to the larger dish turn it over on its distal side . Can you locate Aristotle’s lantern or the “jaws” used by the sea urchin to feed? These jaws are fairly large and capable of crushing and tearing apart shells and other protective layering of prey (including other echinoderms) and the reason why most sea urchins are not considered reef safe. Fortunately, the Tuxedos are one of the few species that only feeds on algae.
Exercise three: Brittle star locomotion
Brittle stars are closely related to sea stairs. Observe the brittle stars we have in lab. You can simply watch them move in response to changing light or a gently prod on your part in the large dishes. Compare their movement with that observed in sea stars.