1. Phylum Cnidaria HW: Study notes & Define Vocab Words.

2. Intro to Cnidarians • How do you say it???? • Say it with me now: (ni DARE ee uh) • Practicing saying this when you are with your friends so you sound smart. • What are cnidarians? • Examples: Jellyfish & Sea Anemones • Are there many species of cnidarians? • Yes, there are 10,000 different species!

3. Body Structure • Like sponges, they have: • One body opening • Two cell layers • Unlike sponges: • Their cell layers are organized into tissues that have specific functions. • They have symmetry

4. Body Structure, cont’d • The function of the two layers: • Outer Layer: protects internal body • Inner Layer: mostly for digestion

5. Cnidarian Symmetry • Cnidarians are radially symmetrical. • Remember what that means???? • Radially symmetrical organisms can detect & capture prey from any direction. • This is especially helpful for the sessile & slow moving cnidarians. • Some cnidarians are aquatic floaters. • Others are sessile. • What’s that again????

6. Feeding & Digestion • What’s a jellyfish look like? • They have long, stinging tentacles. • The tentacles have stinging cells called cnidocytes. (NI duh sites). • They also have nematocysts. • These are capsules that have threadlike tubes that contain poison & barbs.

7. The nifty nematocyst • Nematocysts are like harpoons. • They are propelled by osmotic pressure (water pressure). • When a cnidarian is touched or otherwise stimulated water rushes into the nematocyst (by osmosis) and increases the water pressure, forcing the barb out of the nematocyst. • The force is so strong that the barb can penetrate a crab shell.

8. Feeding & Digestion cont’d • After prey is hit with a nematocysts or cnidocytes (tentacles) the cnidarian brings it to its mouth (it’s only opening). • It then eventually makes it’s way to the gastrovascular cavity. • Cells in the gastrovascular cavity secrete digestive enzymes to break down the captured prey. • Any undigested material is then expelled through the mouth. Yummy.

9. Response to stimuli • Cnidarians have a primitive nervous system known as a nerve net. • These specialized cells can cause contractions of muscle-like tissue. • The movement of tentacles during prey capture is a result of these contractions.

10. Types of organ systems • As we’ve mentioned Cnidarians have: • A primitive digestive system • A primitive nervous system • They do not have: • A circulatory system • A respiratory system • Excretory system • So while they are more complex than a sponge, they are still not very complex creatures.

11. Comparison of Sponges & Cnidarians

12. Vocabulary Review -- HW • Define the following words using your notes: • Radially Symmetry • Sessile • Cnidocyst • Nematocyst • Gastrovascular cavity • Nerve net