Name:
Date:
Biology 11: Kingdom Cnidaria Lab
Purpose:
-To examine members of the Phylum Cnidaria and be able to:
a) Examine and identify the phyla’s unifying characteristics.
b) Describe how the phyla carries out its life functions.
d) Compare and contrast the structure, general function and mobility of Cnidarian polyp and medusa body
plans.
e) Describe the advantages of a mobile stage in the life cycle of Cnidarians.
Observing Living Cnidarians (Sections I and II)
1. Obtain a living Cnidarian from the stock containers and place it in a small dish.
2. Observe the Cnidarian under a dissecting microscope and illuminate it using the overhead light only.
If you use the bottom light you will kill your Cnidarian as the water will become too hot.
Reminder: All drawings must be in pencil and accompanied by magnifications!
Section I: Hydra
Description:
Hydra are small aquatic predators that feed on small zooplankton. They
use their tentacles and cnidocytes to capture prey. Hydra lack a medusa
stage in their life cycle and only exist as polyps reproducing sexually with
gametes or asexually by budding. Hydra are fairly sessile, attaching to an
aquatic substrate and waving their tentacles waiting for prey. They are,
however, capable of locomotion using a somersault or inchworm
approach.
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a) Brown Hydra Observation
1. Follow Observing Living Cnidarians instructions
2. Your hydra may contract into a small ball for several minutes if disturbed. You may need to be patient
and wait for it to relax again.
3. Carefully draw the hydra in the circle below. Label: epidermis, gastrodermis, gastrovascular cavity,
mesoglea, tentacles, mouth, body column and basal disc.
Notes:
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4. Observe your Hydra contracting and extending its tentacles. Do they all extend and contract at the
same time? Why do you think this is?
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5. Describe how your Hydra moves (what type of skeleton does it use to move?). Would you say that it is
sessile, sedentary or motile?
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b) Feeding the Hydra
1. Obtain a sample of living daphnia (water fleas) and place them in the small dish containing your hydra.
Observe the hydra capture and eat the daphnia. Describe this process using appropriate scientific
vocabulary below:
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3. In your own words, define the term cnidocyte and list its functions.
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2. Observe a prepared slide of a hydra tentacle. Draw what you see and label the cnidocytes (stinging
cells).
Notes:
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3. Where do you expect to find the greatest density of cnidocytes? Why does this distribution make
sense?
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c) Budding Hydra
1. Follow Observing Living Cnidarians instructions.
2. Carefully draw what you observe and label an asexual bud. Take special note of the two tissue layers
and the cellular differentiation
Notes:
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Section II: Obelia
Description:
Obelia are polymorphic. Obelia polyps form a sessile colony. There are
two types of polyps in the colony; a feeding polyp equipped with tentacles
surrounding the mouth and a reproductive polyp which produces asexual
medusae by budding. These medusae are free swimming and represent the
sexual stage of the life cycle. At maturity, gonads on each meduase release
gametes (sperm or egg) into the water. After fertilization, the larva locates
a suitable location and attaches to the substrate and develops into a new polyp
colony.
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1. Examine a prepared Obelia slide under a light microscope. Draw what you observe below and label:
Polyp, tentacles, mouth and gastrovascular cavity.
Notes:
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2. How are Obelia similar to Hydra? How are they different?
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3. Obelia follow an Alternation of Generations life cycle, with both a sexual and asexual generation.
Which of these generations does the Obelia colony represent? Why are the benefits of this type of
reproduction?
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Section III: Aurelia
Description:
Marine jellies (or jellyfish) are often encountered along beaches or bay
systems. The large, free-swimming medusa move by pulsing actions of
their bell. Many species have powerful nematocysts used to capture prey
and can deliver an uncomfortable sting to potential predators as well. The
tentacles are positioned along the margin of the bell-shaped medusa. Oral
arms surround the mouth and hang under the bell. Four circular gonads
can be seen in mature specimens during the breeding season.
1. Examine the preserved Jelly sample (or an illustration in one of the books around the lab) and describe
its symmetry and body form.
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2. Where are the tentacles located? ________________________________________________________
3. Locate the gonads in the centre of the specimen.
a) In your own words explain what gonads are and in what stage in the Aurelia lifecycle you would find
them.
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b) How would you describe the shape of the gonads? How many are there?
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4. Define the term mesoglea in your own words and describe where you would find it in the specimen.
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5. Conduct your own research to discover the ecological role of Jellies.
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