Sergio Santiago
Prof. Wilma Giol
Bio II
Introduction:
The Asterias Forbesi or also known as the starfish is a common animal that lives in the ocean floors and reefs. The complete taxonomy is: kindom- animalia, phylum- echinodermata, class- asteroidean, order- forcipulata, family- ateriidae, and genus- asterias or pisasters.
The Starfish has a pentamerous radial symmetry. This means that from the line of symmetry all of its legs are equal. This line of symmetry is traced passing directly in the middle of the aboral surface.
The starfish moves in a peculiar way because it uses a water vascular system to move. What it does is suck in water through the madreporite (small opening on the top of the central disk). Then the water is pushed through the ring canal and into each arm. Finally the water is pushed out through the tubefoot (located in the bottom/ dorsal part) and this causes the starfish to rise and move forward.
The starfish has a basic diet eating things like mollusks, worm crustacean, fish, oysters, and other echinoderms. When the starfish feels the pray it wraps it’s legs around it and with the tubefeet pull the clam open. Then what it does is stick out his stomach and digest the food.
The starfish can do sexual or asexual reproduction, meaning that it can happen inside the starfish and also it could happen outside. The starfish contain some branched ovular sacs (gonads) that open to the exterior that releases the eggs/sperm and these join in order to finish the reproduction.
Some unique qualities that the starfish have are that they have no ears, no eyes, and no nose. This means that the starfish uses its touch to feel around and move. Also they have the ability to regenerate if the have suffered any damage to one of its legs, but if something happens to its aboral disk it dies. The only organ that the starfish has is its stomach, peculiar because it has only one viscera in its whole body.
Materials:
I. Dissection kit includes:
- dropper
- 2 surgical scissors
- disposable scalpel
- dissecting needle, plastic handle
- teasing needle, wooden handle
- forceps
- spatula
- mall probe and seeker
II. Laboratory materials:
- goggles
- dissecting pad
- plastic cover
- plastic gloves
- apron
Procedure:
1. Obtain a preserved starfish and rinse off any preservative with water.
2. Place the starfish in the dissecting pan with its dorsal or aboral (top) surface upward.
3. Observe the starfish and determine its symmetry.
4. Locate the central disc in the center of the starfish. Count and record the number of arms or rays the starfish has.
5. Locate the small, round hard plate called the madreporite on top of the central disc. Water enters through this into the water vascular system. Label the central disc, arms, and madreporite.
6. Turn the starfish over to its ventral or oral surface (underside).
7. Locate the mouth in the center of the central disc.
8. With the starfish's aboral surface facing you, cut off the tip of a ray. Cut along the sides and then remove this flap of skin.
9. Inside each arm, locate two long digestive glands called the pyloric caeca. These make enzymes to digest food in the stomach.
10. Cut a circular flap of skin from the central disc. (You will have to also cut around the madreporite in order to remove this flap.) Observe the stomach under the central disc.
11. Remove the pyloric caeca from the dissected ray. Find the gonads (testes or ovaries) underneath. These may be small if the starfish is NOT in breeding season.
12. Cut off the tip of a ray to observe the parts of the tube feet.
13. When you have finished locate the following: the ampulla, the ossicles, the ring canal, and the stone canal.
Starfish Anatomy:
-Internal Anatomy
o Stomach- digests food inside or outside the starfish
o Pyloric Cecum (Digestive Gland)
o Gonads- branched obulated sacs
o Radial Canal- central ring of the starfish
o Madreporic Plate- pumps in water into the stone canal.
o Stone Canal- place were water enters and goes to the ring canal.
o Ampullae- contracts and the water is forced out the tube foot to move the starfish.
o Ring or Circular Canal- were water is distributed into each arm.
o Pyloric Caeca- secretory gland to aid digestion.
o Esophagus
-External Anatomy
o Madreporic Plate- pumps water into the starfish.
o Spines- gives the starfish some protection.
o Central Disc- were the main components of the starfish are located.
o Ray- is the arm like extremity of the starfish.
o Mouth- through this the starfish eats.
o Tube Feet- it helps to move and also aids in the eating process.
References:
http://www.vsf.cape.com/~jdale/science/science.htm
http://www.k-state.edu/organismic/echinoderms_and_protochordates.htm
http://www.cumberland.k12.il.us/Schools/CHS/Starwalt%20Projects/Starfish/starfish_dissection.htm
