1. Cnidarians Part Deux
HW:

2. Reproduction Most cnidarians have two forms:
Polyp – tube shaped body with a mouth surrounded by tentacles
Medusa – umbrella shaped body and tentacles that hang down. The mouth is on the ventral side between the tentacles.

3. Reproduction
The two forms of cnidarians can be seen in the life cycle of a jellyfish:
The dominant form varies depending on the type of cnidarian.

5. Jellyfish Reproduction
To reproduce jellyfish (in the medusa stage) release egg and sperm into the water.
When the two meet fertilization occurs – in the water not internally.
Resulting zygotes (product of fertilization) will develop into free-swimming larvae that will grow into polyps.

6. Jellyfish Reproduction
Jellyfish polyps reproduce asexually to form new medusae (plural of medusa).
So jellyfish alternate generationally from the polyp stage and the medusa stage.
What does this mean???

7. Cnidarian Diversity
You know that jellyfish and sea anemone’s are cnidarians, but what else is there?
Hydroids
Jellyfishes
Sea Anemone & Coral
How do these three groups consititute 10,000 species????

8. Hydroids Hydroids: ~ 2700 species
Have both polyp and medusa stages in their life cycles.
Most form colonies (like the Portugese Man of War).
Another example of hydroids is the hydra – which we will study.

9. Jellyfishes Jellyfishes: ~200 species
Transparent/transulscent appearance
Medusa is the dominant form, but there is a polyp stage
One well known example is the box jellyfish.
Box jellyfish get their name because the medusa form has a boxlike structure.
A sting from a box jellyfish can kill a human.

10. Sea Anemones & Corals ~ 6200 species (WOW)
Polyp stage is the dominant stage.
Recent research suggests bilateral symmetry for the polyps, unlike jellyfish and hydroids.

11. Sea Anemones & Coral
Sea anemones live as individuals and coral lives in colonies.
Coral secretes calcium carbonate to protect itself.
This creates a hard shell around their soft bodies.
As you may know coral reefs are endangered.
Their health depends on: proper water temperature, adequate light, and appropriate water depth.
Rises in water temperature & pollution pose a threat to this pretty cnidarian.

12. Summary
The notes from the past two days have described the body structure, digestive & nervous systems, reproduction, and diversity of cnidarians.
You need to read & study these notes in addition to completing the labs and color plates!!!!
REMINDER: DO NOT WRITE IN THE COLOR PLATE BOOKS!!!