1. Cnidarians Phylum Cnidaria: “stinging cell” On earth- since 670 MYA
radial symmetry
Germ Layers: 2
epidermal (ectoderm)
gastrodermal (endoderm)
NO ORGAN SYSTEMS
No Segmentation
Movement: sessile or motile
predators
Have tentacles- stinging cells (cnidocyts) , nematocysts “thread cells” used as barbs

3. Structures:
One body opening (mouth) for food to enter and wastes to exit
Gastrovascular cavity: interior cavity where food is digested & nutrients are circulated around the body
Nerve net: net of nerves that allow impulses to travel around the body, senses the environment
Label the hydra on your notes!

4. Without Body Systems, how do they survive?
Nervous: Cephalization absent; Nerve Net-
Skeleton: Hydrostatic- water pressure maintains shape
Respiration: Oxygen diffuses into body from water
Digestion: mouth, GVC
Excretion: simple diffusion into water
Circulation: GVC- gastrovascular cavity
Reproduction: asexual and sexual, alternation of generations

5. Cnidarians: Body Forms
Polyp: body with tentacles facing upward, sessile
Ex: hydra, sea anemone
video polyp predation
Medusa: body with tentacles hanging downward, motile
Ex: jellyfish

6. Cnidarian Reproduction
Asexually: by budding
Sexually: usually in medusa form, sperm and eggs are released into water
(fertilized egg zygote planula larvaadult)
Thousands of gametes are released at a time

7. Alternation of Generations:
Video: medusa releasing from polyp

8. Checkpoint: List 5 traits that cnidarians share.
How many germ layers do cnidarians have? ____ Which are they missing?
Are all cnidarians predators? Motile?
Describe the specialized cells they have on their tentacles.
Describe how a cnidarian consumes and digests food.
Describe the two body forms Cnidarians display, and give examples of each type.

9. Structure:The Polyp and Medusa Stages
Epidermis
Mesoglea
Gastroderm
Tentacles
Mouth/anus
Gastrovascular cavity
Mesoglea
Gastrovascular cavity
Mouth/anus
Tentacles
Medusa
Polyp
basal disc: sticky structure at the bottom of polyp ; sessile

10. Diploblastic - 2 germ layers
Epidermis - outer covering (ectoderm)
Mesoglea - middle non-living jelly-like layer (missing mesoderm)
gastrovascular cavity (endoderm)

11. Classes of Cnidarians
1. Hydrozoa
2. Scyphozoa
3. Anthozoa

12. Class Hydrozoa Freshwater & marine.
Medusa and polyp colonies which appear to be one organism-
different types of polyps work together to serve the entire colony
Ex: Hydra, Obelia, Gonionemus
Physalia (portuguese-man-of-war)
36:40 Ocean Drifters
Asexual repro.-budding.
Sexual repro. via gametes

13. Gonionemus Diagram
mouth
GVC
Gonad
mesoglea
tentacle

14. Class Scyphozoa Scyph= “cup”
Large- Tentacles up to 70 meters in length
All marine
Independent medusa forms
Lack polyp stage or have for a very short time
Ex. Box jellyfish
Big Jelly

15. Class Anthozoa ANTHO=“flower” All polyps-Medusa stage absent
Solitary or colonial
Some produce protective skeletons
All Marine
Ex. Sea anemones, corals

16. Class Anthozoa Sea Anemone
Video jewel anenome

17. Class Anthozoa Metridium
Tentacles
Mouth
Pharynx
Septum
Gastrovascular cavity

18. Symbiotic Relationship

19. Class Anthozoa Corals
Polyp secretes protective skeleton of calcium carbonate
Polyp retracts when not feeding

20. Corals Colony of interconnected polyps

21. Class Anthozoa Meandrina Brain Coral

22. Class Anthozoa Gorgonia Sea Fan

23. Class Anthozoa Tubipora Pipe Organ Coral

24. Class Anthozoa Actinodiscus Mushroom Coral

25. Class Anthozoa Acropora Staghorn Coral

26. Coral Reefs
Formed over 1000’s of years from successive layers of coral skeletons
The underwater equivalent of the amazon jungle- very high species diversity and biomass
Reefs contain:
sponges, colonial hydrozoans, anemones, many varieties of coral, fish, many types of worms we’ve not discussed…not to mention bryozoans, ctenophores, protists, bacteria, etc, etc…

27. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Coral Reef Ecosystem
Photo © McGraw-Hill Higher Education, Barry Barker, Photographer

30. Cnidarian Cladogram Anthozoa Scyphozoa Cubozoa Medusa cuboidal
Loss of medusa
Hydrozoa
Polyp stage reduced
Septa divide gastrovascular cavity
Radial symmetry, cnidocytes, planula larva

31. Checkpoint Cnidarians are diploblastic, what does this mean?
What is the mesoglea?
How are Hydrozoans different from other classes of cnidarians?
List examples of Hydrozoans.
What are scyphozoans, do they have a polyp stage?
Anthozoans are known as the ______________ animals. Give examples of anthozoans.
What is an anthozoan’s protective skeleton made of?
Why are coral reefs important?

32. The End