1. KINGDOM ANIMALIA Phylum Cnidaria

2. Phylum Cnidaria
The phylum name comes from Cnidaria, the Greek word for nettle, a plant that has stinging hairs.

3. Members of the Phylum Cnidaria
…exhibit radial or biradial symmetry.
…are all aquatic (typically marine, but some freshwater).
…are sessile, free-floating, or weak swimming.
…have a tissue-level organization.
…have a primitive nervous system.
…have stinging cells.

4. Question
Which of the following characteristics sets the members of the phylum Cnidaria apart from all other animals?
They are all aquatic.
They have stinging cells.
They are all multicellular.
They are sessile as adults.

5. General Organization
Cnidarian bodies are organized around the gastrovascular cavity, where digestion takes place.
Two layers of cells: gastrodermis (lining the digestive tract) and epidermis (outer layer)
Mesoglea: jelly substance in between the two cell layers.

6. Question
In a cnidarian, the jelly substance in between the two cell layers is called
mesoglea
cnidoglea
epidermis
gastrodermis

7. Reproduction
Sexual reproduction: gametes are shed directly into the water.
Asexual reproduction: usually by budding, some by fission.

8. Question Cnidarians reproduce in all of the following ways, EXCEPT
Asexual fission
Asexual budding
Sexual regeneration
Sexual reproduction involving egg and sperm

9. Life Cycles: Polyp and Medusa
Cnidarians generally alternate between sessile polyps that reproduce asexually and swimming medusae that reproduce sexually.
One of these stages is missing in many forms.

11. Question True or False:
This picture represents the medusa body plan of a cnidarian.

12. Stinging Tentacles
The tentacles of all cnidarians produce nematocysts, organelles that can discharge threads to entangle, penetrate, or poison prey.
The tentacles are composed of cells called cnidocytes, which contain the nematocysts.

13. Cnidocyte

14. Question In a cnidarian, the cnidocytes are used for swimming
digesting food
paralyzing prey
sensing predators

15. Feeding and Digestion
Cnidarians prey on a variety of appropriate-sized prey.
Prey is normally drawn into the gastrovascular cavity by the tentacles.
Here, gland cells discharge enzymes onto the food.

16. Question Where does digestion take place for cnidarians?
In the tentacles
In the epidermis
Outside the body
In the gastrovascular cavity

17. Four Important Cnidarian Classes
1. Class Hydrozoa
Mostly marine
Alteration of generation (polyp and medusa stages) is usually exhibited
Includes hydroids, fire corals, and Portugese man-of-war

18. Hydrozoan: Hydra

19. Four Important Cnidarian Classes
2. Class Scyphozoa
Dominant stage is the medusa
Polyp is absent or reduced
Cup-shaped umbrellas
Includes true jellyfish

20. Scyphozoa: Aurelia labiata

21. Four Important Cnidarian Classes
3. Class Cubozoa
Like jellyfishes, but they have cubical umbrellas.
Some may deliver fatal stings.
Includes the box jelly, one of the 10 most venomous organisms on earth.

22. Cubozoans

23. Four Important Cnidarian Classes
4. Class Anthozoa
Polyps with a flowerlike appearance
No medusa stage
All marine, found all over the world
Includes sea anemones, corals, sea fans, and sea whips.

24. Anthozoans: Corals

25. Anthozoans: Anemones

26. Economic Importance
Reef-building corals provide habitat for fish and other animals that are important as food sources for humans.
Coral reefs are tourist attractions and coral rocks are used as building materials and jewelry.