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Phylum Cnidaria

Phylum Cnidaria. Jellyfish, hydra, sea anemones, & coral. Cnidarian questions. What do we already know about Cnidarians (from the phlyo. Tree) Two tissue layers (germ layers)(ecto and endoderm) “diploblastic” Radial Symmetry 2. Look at the life cycle of a jellyfish…

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Phylum Cnidaria

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  1. Phylum Cnidaria Jellyfish, hydra, sea anemones, & coral

  2. Cnidarian questions • What do we already know about Cnidarians (from the phlyo. Tree) • Two tissue layers (germ layers)(ecto and endoderm) • “diploblastic” • Radial Symmetry 2. Look at the life cycle of a jellyfish… A. What are the two body types of Cnidarians? • Which is mobile? Sessile? • Medusa is mobile • Polyp is sessile

  3. Appearance • Polyp: cylindrical, vase shaped animals that are usually attached to a rock or sea floor Ex. Hydras, sea anemones, corals • Medusa: bell-shaped body; umbrella Ex. Jellyfish

  4. Appearance (cont.)

  5. Symmetry • Radial symmetry

  6. Skeletal/Muscle System • NO MESODERM, so…no real muscles! • most have primitive muscle cells • coral have external skeleton of calcium carbonate

  7. Nematocyst (harpoon) Capturing Prey LET’S EAT!!! • cnidarians are carnivores (eat meat) • use tentacles arranged in a ring around their mouth to capture prey • when a “trigger” is stimulated on a stinging cell called the cnidocyte, a harpoon or nematocyst shoots out & injects poison into the prey Cnidocyte (stinging cell)

  8. Capturing Prey: Cnidocyte and Nematocyst at work Nematocyst (harpoon) Cnidocyte (stinging cell)

  9. Digestion • Sac w/ a digestive cavity (gastrovascular cavity) w/ a single opening that acts as a mouth/anus Jellyfish Hydra

  10. Digestion (cont.) • food is pushed into the gastrovascular cavity where digestion begins (extracellular digestion) • undigested remains leave through the mouth/anus

  11. Nervous System • No brain or even ganglia, no cephalization, etc • Nerve Net- have simple sensory receptors that detect & respond to stimuli

  12. Circulation • NONE!!

  13. Respiration • Diffusion- oxygen from water moves into cells (high to low)

  14. Reproduction • Asexual – budding- formation of outgrowths that pinch off from parent to live independently • Sexual- forms a zygote and free swimming form that settles on ocean floor (usually a polyp) • *MOST ALTERNATE B/W POLYP & MEDUSA LIFE FORM

  15. Reproduction (cont.)

  16. Reproduction (cont.)

  17. Excretion • Diffusion to release waste

  18. Cnidarian Taxonomy

  19. Class Hydrozoa • Ex- Hydra • both asexual polyps and sexual medusa stages • Spends most of its life in the polyp stage • Reproduction: • Sexual: eggs and sperm are shed into the water and form fertilized eggs; planula is by passed with eggs hatching into young hydras • Asexual reproduction via budding

  20. Class Hydrozoa cont. Other Hydrozoans Portuguese man-of-war: Single gas-filled float with tentacles Tentacles house the polyps and modified medusae of the colony

  21. Class Scyphozoa • Jellyfish • The medusae are large and contain massive amounts of mesoglea • Spend most of the life cycle in the medusa phase • Sexual and Asexual reproduction

  22. Class Anthozoa • include sea anemones and coral • Exclusively marine; there is no medusa stage • Most anthozoans are colonial (e.g. corals) and secrete external skeletons composed of calcium carbonate.

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