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Biology LibreTexts

Cnidarians

This laboratory exercise covers the following animals. You should learn this classification scheme and be able to classify the animals into these categories.

Phylum: Cnidaria

  • Class: Hydrozoa (Hydra and relatives)
  • Class: Anthozoa (Sea Anemones and Corals)
  • Class: Scyphozoa (Jellyfishes)

Read the Cnidarians section of the lecture notes.

Hydrozoa

Hydra

1. Use a dropper to place a live Hydra on a slide. Examine the Hydra using a dissection microscope.

Hydra (Live) X 40    
     
Hydra (Live) tentacle
X 100
   

 

Click here: VIDEO - Hydra movement, X40, X100 (3.59 MB)

2. Hydra reproduce both sexually and asexually by budding. Try to find a live Hydra with buds. If you cannot find a live Hydra budding, look for budding in a prepared slide of Hydra.

Hydra budding
This is a form of 
asexual reproduction.
Hydra budding

3. Add a drop of vinegar to the slide containing Hydra. Describe what happened to the cnidocytes.

Hydra (Live) Exposed to
5% Vinegar Solution X 100
Hydra (Live) Exposed to
5% Vinegar Solution X 200

3. Examine microscope slides of hydra l.s. and hydra c.s. Look for the presence of two tissue layers. Identify stinging cells (Cnidocytes) in a slide of the whole animal.

Hydra l.s. X 100 Hydra c.s. X 100 Hydra c.s. X 200
 
Portion of a Hydra tentacle showing cnidocytes 
Hydra l.s. X 40 Hydra l.s. with ingested food X 40

Obelia

1. Examine a preserved specimen of Obelia in a jar.

2. Examine a microscope slide of Obelia. Find feeding polyps and reproductive polyps.

3. Examine a microscope slide of an Obelia medusa. What reproductive cells are produced by Obelia medusae?

Obelia, preserved specimen Obelia Colony X 40 Obelia medusa X 100
     
   
Obelia medusa in feeding
position X 100
   

Other Hydrozoans

1. Examine preserved specimens of Gonionemius, Polyorchis, and Physalia.

Gonionemus, preserved Polyorchis, preserved Portuguese Man-Of-War

Sea Anemones and Coral (Class Anthozoa)

1. Examine a sea anemone and coral.

   
Sea anemone, preserved    
     
Astrangia (Northern Coral)
Skeleton
Coral Skeleton Coral Skeleton

Jellyfish (Class Schyphozoa)

Examine preserved jellyfish on display.

Aurelia