Name______Period ______Date ______

Cnidaria Labs

PART 1: Hydra whole mounts

  1. A “whole mount” (abbreviated w.m.) is an entire organism preserved on a microscope slide; i.e., it is not cut or sectioned in any way. However, it is usually dyed.
  2. Observe Hydraw.m. using amicroscope.Switch between lower and higher power objectives.
  3. Draw the Hydra.There are two slides with Hydraw.m.; look at both but choose one of them to draw. Label the following structures: tentacles, mouth, pedal disk.
  4. To which Class does Hydra belong?
  1. What does “dimorphism” mean?
  1. What body form does this specimen exhibit?
  1. Where might you expect to find a Hydra in the wild?

PART 2: Hydra cross- and longitudinal sections

  1. A “cross-section” (abbreviated c.s.) is a slice of tissue taken through or across the long axis of an organism. If you cut a cucumber into a lot of wheel shapes, then you would be making cross-sections.
  2. A “longitudinal section” (abbreviated l.s.) is a slice of tissue taken along the long axis of an organism. If you cut a large carrot into spears, then you would be making several longitudinal sections.
  3. Observe theHydraslide that has both c.s. and l.s. Switch between lower and higher power objectives.
  4. Draw the c.s. and the l.s. Label the following structures: mouth, epidermis, gastrodermis, gastrodermal cavity, mesohyl.
  5. What are the functions of the Cnidarian mouth?
  1. What is the function of the gastrodermal cavity?

PART 3: Hydra longitudinal section – high power magnification

  1. Higher power objectives usually require a layer of liquid between the slide and the objective lens. That is what you will be using here to observe a Hydral.s. at 1000-times magnification.
  2. This microscope and slide have been set up so that there is already oil on the slide. DO NOT SWITCH BETWEEN OBJECTIVES ON THIS MICROSCOPE.
  3. Observe theHydra.
  4. Draw and label the following structures:epidermis, gastrodermis, cnidocyte, epitheliomuscular cell.
  5. What cell type allows the Hydra to move?
  1. What allows the Hydra to coordinate its movements?


  1. What were you able to see in higher power that you could not see in Part 1 or Part 2?
  1. Bonus: Where does the name Hydra come from? Why is this name appropriate for the creature you see in Parts 1-3?

PART 4: Hydra cnidocytes

  1. This microscope and slide have been set up so that there is already oil on the slide. DO NOT SWITCH BETWEEN OBJECTIVES ON THIS MICROSCOPE.
  2. This slide contains a smear of Hydra cnidocytes.
  3. Draw what you see.
  4. What are the functions of cnidocytes?
  1. What specialized organelle is found inside cnidocytes?

PART 5: Aequorea – whole specimen

  1. Use a stereoscope to observe Aequorea.
  2. Sketch what you see. Label the tentacles and mouth.
  3. What body form does this specimen exhibit?
  1. To which Class does this specimen belong? (You might want to look this up using your phone.)

PART 6: Sea Fan – whole specimen

  1. Use a stereoscope to observe the Sea Fan.
  2. Sketch what you see.
  3. Can you identify individuals?
  1. What body form does this specimen exhibit?
  1. To which Class does this specimen belong? (You might want to look this up using your phone.)

PART 7: Aurelia – whole specimen

  1. Use a stereoscope to observe Aurelia.
  2. Sketch what you see. Label the tentacles and mouth. (Hint: the long, lacey, white structures are not tentacles.)
  3. To which Class does this specimen belong? (You might want to look this up using your phone.)
  1. Bonus: What are those long, lacey, white structures?!

PART 8: Obelia– whole specimen

  1. Use a stereoscope to observe Obelia.
  2. Sketch what you see.
  3. Can you identify individuals?
  1. What body form(s) does this specimen exhibit?
  1. To which Class does this specimen belong? (You should be able to find this in your notes.)

PART 9: Obelia – medusa

  1. Use a microscope to observe the Obelia medusa slide.
  2. Draw what you see. Label the tentacles and mouth.
  3. To which Domain does this specimen belong?
  1. To which Phylum does this specimen belong?

PART 10: Obelia – polyp

  1. Use a microscope to observe the Obelia polyp slide.
  2. Draw what you see. Use page 5 of your notes handout to help you identify and label: tentacles, coenosarc, medusa buds, hydranth.
  3. How many individuals can you count?
  1. How do these individuals live together?

PART 11: Metridium cross-section

  1. Use a microscope to observe the Metridium slide.
  2. Draw what you see. Label the epidermis, gastrovascular cavity.
  3. To which Class does this specimen belong? (You may need to look this up with your phone.)
  1. Compared to the c.s. of Hydra (part 2), how would you describe the anatomy of Metridium?

PART 12: Metridium dissection

  1. You will not begin this portion of the lab until Day 2.
  2. Before you begin, you need:
  3. Gloves, goggles, scissors, forceps, dissecting tray, pins
  4. Awareness of the location and operation of the eye wash station
  5. A specimen – to be shared by 4-5 classmates
  6. Position your Metridium so that the oral side is upward. Identify:body, tentacles, mouth, and pedal disc. Use the figure to assist you.
  7. Lay your sea anemone on its side. Starting at the mouth, cut from the oral disc through the side of the anemone down to the pedal disc. Use the dissecting pins to pin open the sea anemone so that you can observe its internal anatomy. Some additional structures you may not be familiar with:
  8. Acontia: packed with a high concentration of cnidocytes
  9. Mesenteries: a thin layer of mesohyl sandwiched between two layers of gastrodermis. Serve to partition the gastrovascular cavity.
  10. Gonads: produce sperm or eggs.


PART 13: Conclusion Questions

  1. Where do Cnidarians usually live?
  1. Cnidaria have only two cell layers; what is the term we use for this?
  1. Porifera also have two cell layers, but we don’t use that fancy term from Question 2 to describe them. Why not?
  1. What characteristics make Hydra an animal?
  1. How do Cnidarians reproduce?
  1. What major advancements do Cnidarians show compared to Poriferans? Describe how these are advantageous.
  1. What major similarities to Cnidarians show compared to Poriferans?
  1. How do the cells of a Cnidarian get oxygen?

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