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Name _______________________________ Date ______________________ The Hydra: An Unusual Cnidarian Hydras are animals that belong to the phylum Cnidaria. The word Cnidaria means “_stinging nettles_”. Cnidarians use _nematocysts__ to sting & capture their prey then tentacles bring prey to their mouth. Cnidarians have _radial___ symmetry, and use a gut for digestion. Cnidarians come in 2 body forms; a polyp which is shaped like a __vase_, or a medusa, which is shaped like _mushroom__ with tentacles. Unlike most Cnidarians, hydras live their entire lives as polyps. POLYP MEDUSA The nervous system of hydras (and all Cnidarians) consists of a simple network of nerves called a __nerve net___ that controls the movement of the body and tentacles. Messages coming into hydras are gradually spread throughout their bodies by the nerve net. Materials: Pipette Hydra Watch glass Hand lens/ microscope Toothpick Daphnia Procedure: 1. Use a pipette to place one hydra in a watch glass along with some of the water in which it lives. 2. Observe the hydra with a hand lens or under the microscope under very-low power (4X). How many tentacles did your hydra have? ________ 3. Make a drawing of the hydra on page 2 of this lab, labeling the mouth, body, tentacles, and basal disk. 4. While looking at the hydra, gently touch the hydra in three different places with a toothpick. Observe what happens. 5. Place some Daphnia (water fleas) in the dish. Observe what happens. 1 Labeled picture of hydra Analysis: 1. How many tentacles did your hydra have? Do all hydra have the same number of tentacles? (check with other lab groups) ________________________________________________________________ ________________________________________________________________ 2. How is the body shaped? Is that considered polyp or medusa form? ________________________________________________________________ ________________________________________________________________ 3. Where is the mouth located? ________________________________________________________________ ________________________________________________________________ 4. Where is the basal disk? ________________________________________________________________ ________________________________________________________________ 5. When you touched the hydra, did anything happen to suggest that the touch spreads to other areas? What is responsible for this reaction? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 6. What evidence is there to show that the hydra used stinging cells to get food? ________________________________________________________________ ________________________________________________________________ 7. What are 2 ways that the tentacles help the hydra in feeding? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 8. Why is budding considered a form of asexual reproduction? ________________________________________________________________ ______________________________________________________________ 2