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Starfish Dissection
EXTERNAL ANATOMY
Starfish belong to the Phylum Echinodermata, live in water and are predators or
scavengers. The underside of the animal has a mouth and their arms are used to pry
open shelled pry such as mollusks.
1. Place the starfish in your tray with the TOP-side UP. This is the dorsal side of your
starfish.
2. Notice the number of rays from the central disk. How many rays does your
starfish have?__________
3. Use a hand lens to look at the spines that cover the dorsal side of the starfish.
4. Find the small “button” on the central disk. This is the sieve plate.
5. Sketch the DORSAL side of your starfish. Label the sketch Dorsal View. Include
the following parts in your drawing and label: ray, central disk, spine, sieve
plate.
6. Turn the starfish over. This is the ventral side of the starfish.
7. Find the mouth at the center of the rays. Use the hand lens to look at the small
spines around the mouth. These are oral spines. Notice that these are
DIFFERENT from the spines on the rest of the starfish. HOW are they different?
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8. Find the grooves that start at the mouth and go down each ray. There are tube
feet that line each groove.
9. Sketch the VENTRAL side of your starfish. Label the sketch ventral view. Include
the following parts in your drawing and label: mouth, oral spines, groove, tube
feet.
INTERNAL ANATOMY
1. Use the image below to help you dissect and identify the internal parts of your
starfish. NOTE- cut through the DORSAL side.
2. At the center you will find that the starfish has TWO stomachs! The pyloric
stomach and the cardiac stomach right underneath.
3. Find the digestive glands in one of the rays you dissected. They look like a double,
tree tube. The gonads are above the digestive glands.
4. Pull away the digestive glands and gonads to see the single water canal running
along the dissected ray. HOW can you tell the difference between a water canal
and a digestive gland?
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