Starfish Dissection Life Science, Mr. Ditolla

Examine the top surface of your starfish and find the structures labeled below:

Starfish usually have five legs or rays. If a leg gets cut off they can replace it by regeneration. In the middle of the legs is the central disk. The madreporite is used to absorb water for the water vascular system. The water vascular system is a network of canals that the starfish uses for movement. A starfishes skin is covered with spines. The phylum name for starfish is Echinoderm, which means “spiny skin”. Starfish obtain their oxygen through skin gills located on the skin between the spines. Turn the starfish over onto the other side and find the structures labeled on the next slide.

Bottom surface of starfish.

A starfishes mouth is on the bottom and the anus is on the top, which is the opposite of most animals. A star- fish eats clams and uses its tube feet to open the clam shell. Once the clam shell is open the starfish inverts its stomach or turns it inside out. The stomach comes out of its mouth and surrounds the clam, digests it, and then is pulled back through the mouth of the starfish.

Cut the skin off the top of one of the legs and identify the organs labeled below.

Most of the inside of each leg is filled with the hepatic caecum which is a digestive organ used to help digest food. Remove the hepatic caecum and locate the yellow colored gonads. These produce egg cells and sperm cells for reproduction. Remove the gonads and locate the ampullae which are where the tube feet are anchored to the leg. Remove the skin from the central disk and locate the structures labeled on the following slide.

Organs of the central disk.

Throw away the starfish, wipe off your tools, and wash your hands with soap and water. Now answer the following questions on a separate piece of paper: 1.How many legs does a starfish usually have? 2.What happens if a starfish loses a leg? 3.What structure is in the middle of the legs? 4.What is the madreporite used for? 5.What is the water vascular system used for? 6.What is a starfishes skin covered with? 7.What does the word Echinoderm mean? 8.What is unusual about the arrangent of the mouth and the anus on a starfish? 9.What does a starfish use its tube feet for? 10.What does a starfish do to its stomach when it eats a clam?

11. What does the hepatic ceacum do? 12. Where are the gonads located? 13. What are the ampullae? 14. What three structures are located in the central disk? 15. How many stomachs does a starfish have? 16. In what two ways can a starfish reproduce?