1. Phylum Cnidaria (Coelenterata)
Kingdom Animalia
Phylum Cnidaria (Coelenterata)

2. Two Body Forms
Cnidarians include: Jellyfish, Sea Anemones, Hydras, and Corals
All have radial symmetry (“little rings”)
Two body forms:
Medusa- Free-floating, jelly-like and often umbrella shaped
Polyp- Tubelike and usually attached to a rock or other surface

3. Two Body Forms Tentacles surround mouth, located at free end of body
Three layers of cells:
Outer layer from ectoderm
Inner layer from endoderm
Middle layer of mesoglea (jelly-like)
Cells arranged into tissues
Coelenteron- digestive cavity where enzymes digest food

4. Two Body Forms

5. Body Forms Extracellular digestion Cnidocytes
Stinging cells located on the tentacles
Distinguishing characteristic of Cnidarians
Small, barbed harpoon (nematocyst) within each Cnidocyte
Used for defense or to spear prey
Toxins can be deadly or only stun
Extracellular digestion
Digestion begins outside the cell in the gastrovascular cavity
Enzymes break food into smaller fragments
Cells lining cavity engulf fragments and finish digestion intracellularly

6. Class Hydrozoa Freshwater hydrozoa
Genus Hydra exist only as Polyps less than .4” long
Attach to objects with sticky secretion from the basal disk
Can glide on objects or tumble
Have a nerve net- branching system of nerves with no brain

7. Class Hydrozoa Marine Hydrozoa Often live in colonies
Can be medusas or polyps
Ex: Portuguese man-of-war
Physalia- floats on water and dangles tentacles with powerful neurotoxins (nerve poisons)

8. Reproduction in Hydrozoa
Most hydrozoans are colonial and reproduce asexually by budding
Some species are sexual
Most single sexes, but some hermaphrodites
Genus Obelia
Colonize a single polyp with buds
Reproductive polyps produce medusas
Medusas reproduce sexually and produce ciliated larvae called planulae, which develop into new polyps

9. Obelia Reproduction

10. Class Scyphozoa True jellyfish and active predators
Jellyfish relatives:
Cubozoans- Small box-shaped medusas with tentacles on corner of “box”
Inconspicuous polyp stage
Ex: Box jellysish or Sea wasp can be deadly
Phylum Ctenophora- Comb jellies have only a medusa stage and no nematocysts
Class Tenaculata- with tentacles
Class Nuda- without tentacles
Irukandji Jellyfish (Carukua barnesi)
2.5 cm in diameter
Kills in days
True jellyfish and active predators
Range from thimble size to queen-size mattresses
Mostly medusas which reproduce sexually
Polyp stages early in life

11. Jellyfish Relatives

12. Class Anthozoa Some reproduce asexually by budding
Largest class existing only as polyps
Includes anemones, coral, sea pansies, sea fans, and sea whips
Nearly all contain symbiotic algae, dinoflagellates, in exchange for food
Many of the brilliant colors come from the algae
Some reproduce asexually by budding
Others sexual with sperm and egg being released into the ocean where fertilization occurs
Zygotes develop into planulae that settle and develop into polyps

13. Class Anthozoa

14. Class Anthozoa Sea anemones- Small and colorful in coastal areas
Highly muscular- can retract when touched
Reproduce asexually by splitting themselves into two
Corals
Colonies called reefs
Secrete calcium carbonate skeleton that cements to skeletons of neighbors
Top layer is living polyps
Bottom layers are old skeletons

15. Great Barrier Reef