1. Phylum Cnidaria
Chapter 26

2. Cnidaria
A. Contains
1. Corals
2. Jelly fish (sea jellys)
3. Sea anemones
4. Hydra
B. All live underwater and nearly all live in the ocean, and all have external fertilization.
C. Unlike sponges
1. Cnidarians have layers of differentiated
cells
2. Organized into layers of tissue

3. 2. Classes
A. Hydrozoan (hydra) = 3700 species
1. polyps form colonies
2. Portuguese man-o-war is a floating
hydrozoan colony

4. B. Anthozoa
1. Sea anemone and coral = 6100 species
2. grow either as solitary or colonial polyps

5. C. Scyphozoa
1. true jelly fishes (sea jelly) = 200 species
2. adult stage can grow more than 3 m in diameter
3. many are harmless, some are not!

6. D. Cubozoa
1. box jellyfish
2. bell is in a square formation
3. lethal sting – even human!
4. 3 m in length, up to 15 tentacles per side
5. Tropical waters but have been found in eastern pacific regions.
* No chance of surviving
if stung- you will die in
2-3 minutes

7. 3. Phylum Ctenophora
A. Comb jellies
species

8. 4. Body plan = radial symmetry
A. Parts are arranged into circles around a central mouth
1. Medusa form – bell shape form for swimming
B. Top and bottom of animal – no front or back
C. Nervous system present, but no “brain”
1. Nerve net – diffuse web of interconnected nerve
cells which allows for responses to the environment.
D. Ocelli
1. organs able to detect presence or absence of
light

9. E. Statocysts
1. organs which determine which way is up
2. used for balance
F. Muscle like cells
1. contract when stimulated
2. ability for some movement
G. Nematocysts
1. stinging cells used for defense and
catching prey
2. sac containing poison and a tiny spring
like harpoon
3. the box jelly fish has 5000 nematocysts

10. Stingers - Nematocysts

12. 5. Feeding
A. Tentacles capture prey with nematocysts
B. Prey is paralyzed with poison
C. Prey is pushed into the mouth to be digested
D. Waste is expelled back through the mouth
1. Gastrovascular cavity – hollows gut in the center of the body
2. one way in AND out!

13. Life cycle Cnidarians begin their life as a free swimming larva.
It eventually attaches to a hard surface and forms a polyp.
The polyp will bud releasing a medusa that begin its life as a free floating jelly fish.