Printer Friendly
Activity: Nematocysts
NGSS Science and Engineering Practices
NGSS Crosscutting Concepts
Table of Contents


  • Fig. 3.26
  • Fig. 3.28
  • Dissecting scissors
  • Sea anemone, live or frozen
  • Small culture dish
  • Seawater
  • Forceps
  • Dropper bottle of water
  • Microscope slides and coverslips
  • Compound microscope
  • A hair from your head
  • Toothpicks
  • Centimeter ruler
  • Towels


Fig. 3.26. Diagram of a cnidocyte ejecting a nematocyst

Image by Byron Inouye

Fig. 3.28. Anatomy of a sea anemone showing some internal structures. 1. Tentacle, 2. Pharnyx, 5. Septum, 8. Pedal disk, 9. Retractor muscle, 12. Collar, 13. Mouth, 14. Oral disk

Image courtesy of Hans Hillewaert, Wikimedia Commons


  1. Draw a picture of the anemone in your notebook. Label the tentacles and mouth. Use Fig. 3.28 as a reference.
  2. Measure the length and width of the sea anemone using the centimeter ruler. Include a scale in your diagram from Step 1.
  3. With scissors, snip off a piece of a tentacle from a frozen or living sea anemone approximately two millimeters (mm) long. Snipping a tentacle will not harm the sea anemone. Use forceps for handling sea anemones. Do not touch the tentacle with your hands.
  4. Using forceps, place the piece of tentacle on a clean microscope slide. Add a drop of seawater and a coverslip.
  5. Observing your specimen under a com¬pound microscope at 100x, find undischarged, partially discharged, and fully discharged cnidocytes. Use Fig. 3.26 as a reference.
    1. Draw each of the three types of cnidocytes in your notebook.
    2. Label the cnidocil, lid, cell nucleus, nematocyst tube and barbs where applicable.
  6. Test the response of the nematocysts to a hair root
    1. Pull out a head hair with a root.
    2. Insert the root of the hair under the coverslip, touching the tentacle tis¬sue while your partner watches through the microscope.
    3. Pull the root slightly away from the tentacle.
    4. Observe how the nematocysts react to the hair root.
  7. Test the response of the nematocysts to saliva.
    1. Place several drops of saliva on one end of a second glass slide.
    2. Get a fresh piece of tentacle and place it close to the saliva.
    3. Move the saliva onto the tentacle with a toothpick while your partner watches the tentacle through the microscope. After using the tooth¬pick, break and discard it.
    4. Describe how the tentacle responds to the saliva.


Activity Questions
  1. Were you able to find undischarged, partially discharged, and fully discharged cnidocytes? Explain.
  2. Did the cnidocytes you observed differ in shape from the cnidoctes shown in Fig. 3.26? Explain.
  3. In Step 4 and 5, which stimulant, hair or saliva, caused the firing of more nematocysts? Explain.
  4. Why is it important to use forceps when handling sea anemones in this activity?
  5. What safety concerns would you advise about handling sea anemones or other cnidarians in the ocean or washed up on the beach?
  6. If a cnidarian has just finished feeding, predict whether it will discharge more nematocysts if the tentacles touch an¬other piece of food. Explain your rea¬soning.
  7. What might explain why some people get severe reactions to Portuguese man-of-war stings but others do not?
  8. Use the following terms to describe a sea anemone, a Portuguese man-of-war, or another cnidarian:
    1. ectoderm
    2. nematocyst
    3. venom
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.