Cnidaria

The Phlyum Cnidaria

Supplementary Reading (required):

Additional useful readings (required for Bio 351 but not required for Bio 152):

1. Diverse group

2. Great impact on world.

3. Some in freshwater, but mostly marine

4. Very common and abundant

5. Major body forms: polyp and medusae

6. Simple nervous system

7. Nematocysts: function in prey capture and defense (see diagram)

7. General cnidarian life cycle:

8. Major groups (oversimplified - several classes are left out):

9. Examples of the three major classes:

Hydrozoans:

Scyphozoans:

Anthozoans:

10. The general structure of a stony coral:

First a diagram:

Now an example of the real thing (closeup of a bird's nest coral, Seriatopora hystrix, in Augsburg's Coral Reef Aquarium):

Finally, a short time-lapse movie showing growth in a sony coral:

(Note: This and an additional movie can be found at: http://mars.reefkeepers.net/movie.html.

You'll need the Shockwave Plugin to view the other movie though)

11. Diverse modes of nutrition in different species:

most species utilize several modes of nutrition
prey capture (often involving nematocysts...see below)...prey may be large or small, depending on species.
phytoplankton capture (example of a phytoplankton feeder)
bacterioplankton capture (e.g. small polyped stony corals...birdsnest coral pictured here)
trapping tiny organic particles in mucus, move to mouth with cilia (e.g. pulsing Xenia soft coral)
direct absorption of dissoved organics
symbiotic dinoflaggelate algae (zooxanthellae) - very common
all reef building corals have zooxanthellae and get a significant amount of energy from the products of photosynthesis from their algal symbionts

12. Interactions with other organisms, impact on environment

Coral reefs - "rainforests of the sea"
Coral reefs <1% of ocean area but home to half of all marine fish species! (approx. 7000 species of reef fish worldwide!!!)
LOTS of other diversity in reefs too - algae, corals, sponges, worms, crustaceans, tunicates, etc.
Reef structures protect shorelines (see aerial photos of Rarotonga1, Rarotonga2 , and Great Barrier Reef)
Sybioses/mutualisms with cnidarians are common - e.g. anemonefish, shrimp

butterflyfish - many species feed on corals or anemones

nudibranchs - many feed on cnidarians, some use "stolen" nemaocysts for defence!

flamingo tongue snail - feeds exclusively on gorgonians (this one in the photo is eating a live sea fan)