1. Cnidarians Phylum Cnidaria: “stinging cell” Hollow gut- (coel)
On earth- since 650 MYA
radial symmetry
Germ Layers: 2
epidermal
gastrodermal
NO ORGAN SYSTEMS
Segmentation: none
Coelom: Acoelomate
Movement: sessile or motile
Have tentacles- stinging cells found on tentacles

2. 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
NEMATOCYSTS tentacles that contain stinging cells(cnidocysts) used to capture and poison prey
Label the hydra on your notes!

3. Without Body Systems, how do they survive?
Nervous: Cephalization absent; Nerve Net-conducts impulses
Skeleton: Hydrostatic- water pressure maintains shape
Respiration: Oxygen diffuses into body from water
Digestion: one body opening for food & wastes
Excretion: simple diffusion into water
Circulation: none
Reproduction: asexual and sexual, alternation of generations

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

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

6. Answer the following:
Explain why sponges and cnidarians release so many gametes into the water

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

8. 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

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

10. Classes of Cnidarians
Hydrozoa:fresh water and marine, polyp and medusa present ex. Hydra, man-o-war, Obelia
2. Scyphozoans: cup- large jellyfish ex. box
3. Anthozoans: flower -all marine -polyps only
Ex: corals, sea anemone
Riches of the sea

11. 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)
Asexual repro.-budding.
Sexual repro. via gametes

12. 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

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

14. Class Anthozoa Sea Anemone
Video jewel anenome

15. Class Anthozoa Metridium
Tentacles
Mouth
Pharynx
Septum
Gastrovascular cavity

16. Symbiosis

17. Class Anthozoa Corals Protective skeleton of calcium carbonate
Polyp retracts when not feeding

18. Corals Colony of interconnected polyps

19. Class Anthozoa Meandrina Brain Coral

20. Class Anthozoa Gorgonia Sea Fan

21. Class Anthozoa Tubipora Pipe Organ Coral

22. Class Anthozoa Actinodiscus Mushroom Coral

23. Class Anthozoa Acropora Staghorn Coral

24. Coral Reefs
Formed over thousands of years from successive layers of coral skeleton deposits (calcium carbonate forms underwater mountains of coral animal 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..

25. 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

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

27. The End