Watch their movements and examine their structure closely under the dissecting scope. Lay the sea urchin on its aboral surface and examine the area close to the mouth under the dissecting scope, making sure there is adequate light. You should see the pedicellariae near the mouth. These structures are involved in cleaning debris from the urchin, defense against potential predators, and they actually 'prey' on small organisms such as brine shrimp. The mouth itself is surrounded by five teeth , which are connected to the internal chewing structure called the Aristotle's lantern .
Sea urchins are primarily herbivorous.
We will also have several live starfish for you to examine. You can see the central disk on the aboral side. You will also see a distinct circular area near the edge of the central disk. This is called the madreporite , which is the entrance to the water vascular system of the starfish. The fleshy projections along the surface of the body are dermal branchae , which function in gas exchange.