1. Jellyfish, Coral, Sea Anemone, and Hydroids
Phylum Cnidaria
Jellyfish, Coral, Sea Anemone, and Hydroids

2. Cnidarians Stinging cell animals
Also Known As: Coelenterates: “Hollow Gut”
Radial Symmetry: similar body parts surrounding a central axis

3. Body Plan No segments: oral and aboral sides
Hydrostatic Skeleton: fill body cavity with water to remain upright.
Shrink down as defense
Organized at tissue level. (No true organs)
Epidermis: outer cells (ectoderm)
Gastrodermis: lines gastrovascular cavity
(endoderm)
Mesoglea: middle layer of gelatinous material; can be thick or thin.

5. Digestion
Food is digested in the sac-like digestive cavity (only one opening)
Extracellular and intracellular digestion
Extracellular: outside of cells
Intracellular: inside of cells
Waste is expelled out of the mouth

6. Unique Features Cnidoblasts: stinging cells
Inside each cell is a nematocyst, coiled thread with barb at the end.
The nematocyst can be discharged by either physical or chemical stimulus.
Physical- cnidocil (modified flagella) acts as a trigger
Contain a poisonous neurotoxin, varies by species

7. Life Cycle Jellyfish have separate sexes
Both sexual and asexual reproduction
Sexual: external or internal (depending on species), sperm and egg form a zygote which grows into a swimming larva called the planula.
In some cases the planula attaches to a hard substrate and develops into a polyp.

8. Life Cycle cont. The polyp resembles an upside-down jellyfish medusa.
Small umbrella like medusas break off from the polyp by budding (asexual)

9. Classification of Cnidarians
Class Hydrozoa- Hydra, Physalia, and Obelia
Class Scyphozoa- True Jellyfish
Class Cubozoa- box jellyfish
Class Anthozoa- Corals and Sea Anemones

10. Class Hydrozoa Usually colonial, except Hydra
Composition of colonies- 3 types
1. Gastrozoid- responsible for feeding
2. Gonozoids- responsible for sexual reproduction
3. Dactyliozoids- responsible for defense; have numerous nematocysts.

11. Class Scyphozoa All marine; medusa is dominant life cycle
Mesoglea is a large part of the body (mostly dead matter)
Gastroderm have nematocysts; food may be eaten alive
More toxic than hydrozoans
Well developed sensory organs and glands
- eyespot and chemoreceptors

12. Class Cubozoa Cube-like jellyfish
Have four flattened, blade-like structures called pedalia
Complex eyes with lenses and retinas (no brain though)
Only 16 species: Irukandji and Chironex- deadly box jellyfish. Can kill a human in minutes.

13. Irukandji: Carukia barnes
One of, if not the deadliest box jellfish.
2.5 cm (1 inch) in diameter

14. Class Anthozoa No medusa stage in life cycle
Polyps produce eggs and sperm that develop into planula larva
Solitary: sea anemone
Colonial: coral

15. Corals and Coral Reefs Corals are colonial cnidarians
Dominant form is the polyp
Coral reef is a massive structure composed of calcium carbonate built by coral polyps and the organisms that live with them
The polyps take up calcium in the sea water and zooxanthellae, which live inside the polyp, take up CO2, which make limestone

16. Coral Reefs Found only in tropical areas Warm and clear water
Shallow water- zooxanthellae require sunlight to photosynthesize
Zooxanthellae are the primary producers of the coral reef

17. Coral Reef Formation
Fringing Reef: occurs when a seamount pierces the sea surface to form an island and provides a base on which the coral can grow
Barrier Reef: occurs if a seamount subsides slowly enough and the coral continues to grow upward at a rate that is not exceeded by the rising water. A lagoon is formed.
Atoll- occurs if the seamount disappears below the surface and the coral reef is left as a ring.

18. Symbiosis and Cnidarians
Symbiosis: literally means to live together
Mutualism: both organisms benefit from living together
Commensalism: one organism benefits, the other is unaffected
Parasitism: one organism benefits, one is harmed.

19. Sea Anemones and Clownfish
Usually, fish the size of clownfish are stung and eaten by an anemone
Clownfish become immune to the anemones nematocysts because of a mucus coating
The mucus inhibits the anemone’s sting
The anemone provides protection and scraps of food for the clownfish
The clownfish lures prey into the anemone and cleans the anemone
What kind of relationship is this?______________

20. Corals and Zooxanthellae
Zooxanthellae are dinoflagellates that are taken up by the coral polyps.
Zooxanthellae contain chloroplasts
Coral use the glucose made by the zooxanthellae as an energy supplement
The zooxanthellae benefit because they are protected and receive nutrients from the coral polyp.
What type of relationship is this? _____________

21. Phylum Ctenophora Comb Jellies
Take notes on your own sheet of paper, only write down what is underlined.

22. Ctenophora Group of 100 species Oval shaped with radial symmetry
Resemble cnidarians but are NOT!
Swim with 8 rows of ciliary combs (long cilia fused at the base)
Cilia refract light which
cause a rainbow effect.
Body length varies from a few centimeters to 2 m long.

23. Habitat
Exclusively marine
Can be found in cold or warm water

24. Diet Carnivores Consume fish larvae and plankton
Can expand stomach to eat organisms twice their size.
Capture prey with two long tentacles armed with sticky cells called colloblasts
A few species have nematocysts

25. Reproduction Sexual reproduction Hermaphrodites
No polyp form; only medusa