1. Cnidarians (phylum Cnidaria)
Include hydra, jellyfish, sea anemones,and corals.

2. Cnidarians
Have two body forms: polyp (sessile) & medusa (free-swimming, motile).
Have only one body opening.

3. Cnidarians: Have stinging cells called nematocysts.
Nematocysts are found in tentacles which surround the mouth.
Body is made up of two cell layers.
Have simple nervous systems.

4. Two Cell Layers Ectoderm – Outside layer of epidermal cells
Gastrodermis/ Endodermis
Inside layer of cells
Contains digestive cells
Mesoglea
– Contains the
nerve net
Jelly
like substance

5. Cnidarian Feeding Habits
1. Prey touches a tentacle…
2. Nematocysts fire, paralyzing prey, toxin is injected...
3. Tentacle contracts, prey is forced into mouth…
4. Prey is digested in gastrovascular cavity.

6. Cnidarian Feeding Habits
Since cnidarians only have one body opening, undigested food must be ejected back out through the animal’s mouth!

7. Cnidarian Fact:
Unlike sponges, cnidarians have a nerve net, which conducts impulses throughout their bodies and brings about contractions of musclelike cells.

8. Cnidarian Systems Symmetry Radial Support none Digestive nematocysts
Gastrovascular cavity
Circulatory
None

9. Cnidarian Systems continued
Respiratory
diffusion through cells
Nervous
Nerve net
Reproductive
Asexual - budding
Sexual

10. Examples of Cnidarians
Corals produce a hard calcium carbonate skeleton for protection.
Form into large colonies
Living organisms

11. More Examples Sea Anemone
Large example that is sessile with a large accordian shaped gastrovascular cavity

12. More Examples Jellyfish
There are hundreds of different examples of jellyfish
Many are deadly poisonous while others are not at all.
They are the medusae stage

13. The Portuguese Man o’ War
Click

14. Jellyfish Lake, Palau