1. Cnidarians
An Overview

2. Classes of Cnidarians Hydrozoa- Hydra Scyphozoa- Jellyfish
Anthozoa- Anemones

3. General Form
Soft bodied
Stinging tentacles in circle around mouth

4. Characteristics
Respiration: Through diffusion (directly through tissue)
Excretion: Through diffusion
Feeding: NEMATOCYSTS poison prey, tentacles bring prey to mouth; many cnidarians have photosynthetic protists living in them (symbiotic relationship)

5. Internal Transport: Mostly diffusion of gases/wastes & nutrients
Response:
STATOCYSTS are involved in balance (up/down position)
OCELLI “eye spots” detect presence of light
NERVE NET- primitive nervous system

6. Jellyfish Ocelli
The red dots at the base of the bell on this jellyfish are the ocelli eye spots) used to detect arease of light & dark

7. Reproduction: Sexual- release gametes into water; Asexual- through budding off of a polyp

8. Movement: Epidermal cells expand & contract to help move tentacles & propel animal through water (on jellyfish, the bell shaped body contracts)

9. Usually exist as polyps
HYDROZOANS
Usually exist as polyps
Asexual or sexual reproduction (some hermaphroditic- both sexes)
Polyps have special jobs when living in a colony

10. Most of life spent as a medusa Known for having nematocysts
SCYPHOZOANS
Most of life spent as a medusa
Known for having nematocysts
* When stimulated, harpoon releases toxin to poison & kill prey
Both sexual & asexual reproduction

11. Sexual & asexual reproduction
ANTHOZOANS
Only polyp stage
Sexual & asexual reproduction
Have photosynthetic symbionts (contribute energy)
Corals exist as colonies & have hard outer shell which houses polyps

12. Cnidarians in our World
Economic Importance
Ecological Importance
Coral reefs provide habitat for fish that are harvested by humans
Coral jewellery
Research: anticancer drugs, study of nerve net function
Form symbiotic relationships with other animals
Corals make up reef habitat

13. Jellyfish Facts
1. Jellyfishes are made up of more than 95% water. Their bodies are soft and lack a skeletal structure or outer shell. They are delicate and easily damaged. 2. The largest jelly has a bell that reaches 8 feet across & tentacles that extend ½ the length of a football field

14. 3. Jellyfish are considered a delicacy by some- they can be eaten dried & salted or cooked

15. 4. An adult jelly is called a Medusa- it gets its name from the Gorgon Medusa of Greek mythology with hair of writhing snakes.

16. 5. Australia’s box jelly is the most dangerous jellyfish… its toxin is more potent than cobra venom & can kill a person in minutes.