1. Phylum Cnidaria

2. Classes: We are only going to talk about 4 classes
Hydrozoa: Portuguese Man-of-War, hydra, Obelia Scyphozoa: True Jellyfish Cubozoa: Box Jellyfish Anthozoa: Sea anemones, Coral, and Sea fans

3. Hydrozoa 2700 species Two groups: Hydroids Siphonophores
Mainly marine animals
Two life stages
Polyp (hydra’s only have polyp stage)
Medusa
Found in mainly in polyp colonies

4. Scyphozoa 200 Species True Jellyfish Marine coastal waters Two stages
Polyp (restricted to small larval forms)
Medusa

5. Cubozoa 20 species Marine coastal water Two Stages Polyp
Medusa (dominate stage)
Square shaped when viewed from above

6. Anthozoa 6200 species Marine coastal waters One stage Polyp only
Most live in colonies
Coral Reef

7. Characteristics
Radial Symmetry

8. Characteristics Gastrodermis One body opening
Two cell layers are organized into tissues with specific functions.
The inner layer is adapted mainly to assist in digestion.
Oxygen dissolved in water can diffuse directly into body cells.
Carbon dioxide and other wastes can move out of a cnidarian’s body cells directly into the surrounding water
Gastrodermis

9. Characteristics Two stages Polyp Medusa
One body form may be more observable than the other.
In jellyfishes, the medusa is the body form usually observed.
The polyp is the familiar body form of hydras

10. Life Cycle & Reproduction
Medusa only life cycle
Polyp only life cycle

11. Life Cycle & Reproduction
All cnidarians have the ability to reproduce sexually and asexually.
Sexual reproduction occurs in only one phase of the life cycle
It usually occurs in the medusa stage, unless there is no medusa stage then the polyp can reproduce sexually
Sexual
Reproduction
Asexual
Reproduction
sperm
egg

12. Digestion
Cnidarians are predators that capture their prey using nematocysts
A nematocyst is a capsule that contains a coiled threadlike tube
May be sticky or barbed, and it contains toxic substances
Nematocysts are located in stinging cells called cnidocytes, on the tentacles

13. Digestion Hydra eating a daphnia
Once captures by nematocysts, prey is brought to the mouth by contraction of the tentacles
Prey is moved to the gastrovascular cavity
The cells that line the gastrovascular cavity release enzymes over captured prey. Any undigested materials are ejected back out through the mouth.

14. Nervous system
A cnidarian has a simple nervous system without a control center, such as a brain like that of other animals.
In cnidarians, the nervous system consists of a nerve net that conducts impulses to and from all parts of the body
The impulses from the nerve net cause contractions of muscle-like cells in the two cell layers.