Investigation: Hydra

Materials: Slides of preserved hydra (budding) or living specimens of hydra, microscopes

Prelab Questions:

1. The Hydra belongs to the Kingdom _________________________
and the Phylum __________________________________________

2. What are cnidocytes?

3. Where do hydra live?

4. Name two other organisms that are closely related to the hydra.


View a Hydra

Obtain a slide of a living or preserved hydra and observe under scanning and low power. DO NOT use high power.

1. Draw the hydra as it appears at 40x (scanning) and label the basal disk, tentacles and the gastrovascular cavity. 

Use an arrow to indicate where the mouth of the hydra is (you may not be able to see it on your specimen)

hydra sketch


2. Count the number of tentacles on your specimen.  How many are there? ___

Compare this number to other hydra in the room. Do all hydra have the same number? ____

If someone asks you "how many tentacles do hydra have?" How would you answer?


3. A single tentacle has several nematocysts which can be viewed as small bumps on the surface of the tentacle. Nematocysts contain the stinging cells (cnidocytes). Sketch a tentacle as it appears at 100x (low power) and label the nematocysts.

Estimate the number of nematocysts on a single tentacle: ________