1. Jelly-fish, coral, sea anemones, and hydras
Phylum Cnidaria
Jelly-fish, coral, sea anemones, and hydras

2. Characteristics of Cnidarians
Cnidarians have two tissue layers and radial symmetry
Epidermis,
Gastrodermis
Mesoglea is the jelly – like substance between the layers.
Cnidarians have two basic body forms
Medusa, free floating and are often umbrella shaped
Polyp, tube - like and attach to a rock or some other object

3. Visual Concept: Comparing Medusa and Polyp Bodies

4. Differentiation of Cells
Cnidarians have nerve cells arranged into nerve net
Sensory cells
Muscle - like cells
Stinging cells (cnidocytes)

5. Stinging Cells: Cnidocytes
Cnidocytes are located on fingerlike tentacles that surround the one opening.
Each cnidocyte has a threadlike organelle called a nematocyst
That can contain toxins
Used for defense and to capture prey

6. Visual Concept: Cnidocytes

7. Reproduction Sexual and asexual reproduction occurs in both forms
In Obelia, the life cycle alternates between a polyp and a medusa stage.
Once the gametes fuse, a planulae forms as a free-swimming larvae.

8. Obelia Life Cycle

9. Groups of Cnidarians The three main groups of cnidarians are;
Class Hydrozoa (Colony, Portuguese man – of – war)
Class Scyphozoa (Common jelly fish)
Class Anthozoa (“flowering” animals, sea anemone)
Class Cubozoa (box jellies, once in Scyphozoa)

10. Class Hydrozoa Primary polyp form
Colonial organisms, example Obeila pg 678
Polyps in colony have specialized “jobs”

11. Class Scyphozoa “cup animals” Aurelia
Includes both polyp and medusa forms

12. Class Anthozoa
“flower animals”
Polyp major form

13. Class Cubozoa Box jellies, Sea Wasp Chironex fleckeri
Cube – shaped medusae with 1 – 2 tentacles on each corner
Polyp is inconspicuous
Very small and poisonous

14. Phylum Ctenophora: Comb Jellies

15. Phylum Ctenophora: Comb Jellies
“comb – holder”
8 comb – like rows of cilia
Move by beating their cilia
Most do not have cnidocytes, instead colloblasts
Secrete sticky substance on two tentacles
Apical organ, direction in water
Hermaphroditic
Bioluminescent