1. Chapter 13:
Phylum Cnidaria

2. Cnidocyte- Stinging cell
Nematocyst-Stinging organelle or capsule
Cnidarians get their name by having Cnidocytes

3. Simple animals – 9000 species
Longest fossil history of any other metazoan – 700 million years
3 layers thick
Epidermis-outer layer
Mesoglea-middle layer

4. Gastrodermis -surrounds the gastrovascular cavity

5. Most sessile/ or weakly swim
Effective predators that kill and eat prey much more highly organized and intelligent
Tentacles with cnidocytes
Contain stinging organelles called nematocysts

6. Penetrates it’s prey and injects it with paralyzing toxins
Prey is injected with hundreds even thousands of nematocysts
Even humans can be harmed
Found in mostly shallow waters
Marine / some fresh water

7. Radial or biradial symmetry
No head region interacts with it’s environment from all sides

10. Hydra

13. Four Classes of Cnidaria
Hydrozoa
Hydroids
Fire Corals
Portuguese Man-o-War
Syphozoa
True Jellyfish

14. Cubozoa
Cube Jellyfish
Anthozoa
Largest class
Sea Anenomes
Stony Corals
Soft Corals

15. Form and Function Dimorphism and polypmorphism
Existence of different forms or body types
Two morphological types
Polyp
Hydroid form
Sessile

16. Medusa
Jellyfish form
Floating or swimming

18. Nematocysts: The Stinging Organelle
Capsule
Similar to chitin
Coiled tubular filament
May bear tiny barbs or spines
Discharges due to vibrations or swimming prey
Nematocyst is then replaced

19. Osmotic pressure also helps trigger the nematocyst
Some do not penetrate prey but coil around the prey or stick to the prey
Portuguese Man-o-War and some jellyfish can harm even kill humans

20. Nerve Net Diffuse nervous system
Nerve cells found in the epidermis and gastrodermis
Form two interconnected nerve nets

21. Nerve impulses are transmitted from one cell to another by release of neurotransmitters from small vescicles on either side of the cell
One way transmission is ensured in higher animals because the vesicles are located on only one side

22. Reproduction Sexual/Asexual Polyps – budding
Buds of side of animal or tiny medusas float off
Fission – reproduction by dividing body
External fertilization – separate sexes
Zygote forms polyp then medusa

24. Ecology of corals Light, temp, depth
Mutualistic relationship with algae
Gives corals the nutrients and energy to lay down calcium carbonate – hard parts of coral
60 % of energy comes from algae

25. Environmental problems
High temps can kill algae
Leaves transparent cells on white skeletons
bleaching
Becoming more common and severe
Corals eventually die
Global warming contributing to problem

26. Human activity-diving
Silt,sediment – logging,farming,mining,construction
Fertilizers,insecticides,industrial pollutants
Overfishing