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On the Cutting Edge: Starfish Anatomy


The sea star, or starfish, is a marine invertebrate belonging to the phylum Echinodermata (from the Greek for spiny skin). It exhibits radial symmetry, with 5 arms extending from a central disk. Introduce your students to the external anatomy of the sea star using the dissection guide below and explore the interesting structures that function in protection, locomotion, and feeding.

Sea star dissection guide

  1. Place the specimen on its dorsal surface with the oral side upward.
  2. Along the midline of each arm is an ambulacral groove lined with rows of tube feet.
  3. Find the mouth, in the center of the central disk.
  4. Turn the sea star over and examine the aboral side.
  5. Observe the protective spines along this side. These spines extend from the calcium carbonate plates below the body wall, which make up the endoskeleton of the animal.
  6. At the base of many of these spines are pedicellariae, tiny pincers that grasp objects and help clean debris and parasites from the body.
  7. Locate the madreporite, also known as the sieve plate. The madreporite is a light colored, circular plate found between 2 arms. This structure is the entryway of water to the water vascular system.
  8. Place the sea star with oral side upward. Observe the tube feet closely. Each consists of a cup-like sucker. The sea star moves along by the action of the tube feet. They are also used to attach to the shells of bivalves and pull the shells apart, exposing the soft tissue of prey.

The next step

Now your students are ready to learn about the sea star’s internal anatomy—and Carolina’s Starfish Dissection BioKit® is a great resource to teach the anatomy of this echinoderm. The kit includes 30 starfish, 30 self-locking storage bags, 30 student guides, and a teacher’s manual.

Additional resources

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