Unveiling the Fascinating World of Cnidarians

1. PHYLUM CNIDARIA(Sea Anemones, Jellyfish, Coral, Hydras) ~10 000 species FACT: Cnidarians have a single external opening that serves as both the mouth and the anus!

2. CNIDARIA • Cnidaerefers to the creatures’ “stinging cells” • Are further up the “evolution ladder” • meaning they are more complex than Porifera (sponges) • Three Classes • Class Hydrozoa • Class Scyphozoa • Class Anthozoa

3. CNIDARIA • MULTICELLULAR • cells are specialized and organized into tissues and sometimes even into simple organs • all Cnidarian have specialized defense cells that sting = cnidocytes • cnidocytes (the cell) contain a unique organelle = called nematocyst = “stinger” • GERM LAYERS • Only endoderm and ectoderm • Endoderm – forms inner gastrodermis • Ectoderm – forms outer epidermis

4. CNIDARIA • MOVEMENT • medusa form (bell-shaped) is motile (moving) • polyp form (vase-shaped) is sessile (non-moving) • some cnidarians exist in both forms throughout their life cycle (alteration of generations) • medusa polyp • (motile) (sessile)

5. CNIDARIA • Two body forms • Polyp • Tubular shape • Mouth faces upwards • Sessile • Medusa • Mouth faces downwards • Motile (drifters)

6. CNIDARIA • REPRODUCTION • Asexual – budding • Sexual – monoecious, produce both sperm and eggs • Sexual – male (produce sperm) • - female (produce eggs)

7. CNIDARIA • no body cavity because no true mesoderm • radial symmetry • non-segmented • have tissues • gastrodermis (gas exchange and digestion) • epidermis (protection) • middle layer = mesoglea (jelly-like) • have a “nerve net”

8. CNIDARIA • DETAILED STRUCTURE (Example of Hydra)

9. CNIDARIA • BODY SYSTEMS • REPRODUCTIVE SYSTEM – a rudimentary system in some organisms • Asexual Reproduction • budding (no system) • Sexual Reproduction • Monoecious = individuals produce both sperm (testis) and eggs (ovary) • Dioecious= male produce sperm (testis) and females produce eggs (ovary)

10. CNIDARIA • BODY SYSTEMS • REPRODUCTIVE SYSTEM and LIFE CYCLES • Alternation of generations • Aurelia (jelly fish) Obelia (hydra) • http://trc.ucdavis.edu/biosci10v/bis10v/week9/moonjellemba.mov

11. CNIDARIA • BODY SYSTEMS • DIGESTIVE SYSTEM – not a true system • food enters gastrovascular cavity via mouth • extracellular digestion (enzymes secreted into cavity) • cells lining the cavity absorb digested nutrient and smaller food particles

12. CNIDARIA • BODY SYSTEMS • CIRCULATORY SYSTEM – not a true system • nutrients and gasses diffuse directly across the thin cell layers • RESPIRATORY SYSTEM – not a true system • gas exchange directly between cells and water by diffusion (O2diffuses into and CO2 out of cells) • Both across epidermis and gastrovascular tissues

13. CNIDARIA • BODY SYSTEMS • EXCRETORY SYSTEM – not a true system • waste diffuses from cells into gastrovascular cavity • waste is then released through the mouth • MUSCULAR SYSTEM – NONE • no muscle cells but some cells can contract and relax (e.g. in the tentacles) • SKELETAL SYSTEM – NONE

14. CNIDARIA • BODY SYSTEMS • Nervous System – a basic system • a net of nerve cells • react to presence of food and danger • for feeding and protection • Hydra Feeding

15. CNIDARIA • GENERAL INFORMATION • HABITAT • mostly marine waters (marine = salt water) • some freshwater species • SIZE • as small as 0.5 cm tall • bell of up to 2.4 m diameter and tentacle ranging upwards of 50 meters

16. CNIDARIA - Class Hydrozoa • colonial organisms • hydras, Portuguese Man-of-War • medusa and polyp forms

17. CNIDARIA - Class Scyphozoa • “Cup Animals” • jelly fish • predominantly in the medusa form

18. CNIDARIA - Class Anthozoa • “Flowering Animals” • sea anemones • coral • predominantly in the polyp form • sea anemone coral • and clown fish

19. http://www.youtube.com/watch?v=pYUZxS1bZR4 = Steve Irwin and Box Jelly