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Phylum Cnidaria

Phylum Cnidaria

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Phylum Cnidaria

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  1. Phylum Cnidaria

  2. General Characteristics • They are radially symmetrical • They have 2 tissue layers: • Epidermis - Outer layer of cells • Gastrodermis Inner layer which lines the gut cavity or gastrovascular cavity • In between these tissue layers is a non-cellular jelly-like material called mesoglea

  3. Cnidarian Body Plans • Polyp form • Tubular body, with the mouth directed upward. • Around the mouth are a whorl of feeding tentacles. • Only have a small amount of mesoglea • Sessile • Medusa form • Bell-shaped or umbrella shaped body, with the mouth is directed downward. Hydras, sea anemones, corals • Small tentacles, directed downward. • Possess a large amount of mesoglea • Motile, move by weak contractions of body

  4. Skeletal/Muscle System • most have primitive muscle cells; coral have external skeleton of calcium carbonate

  5. Stinging Organelles • cnidarians are carnivores (eat meat) that use tentacles arranged in a ring around their mouth to capture prey • Prey is captured by using specialized stinging cells called cnidocyteslocated in the outer epidermis. • Each cnidocyte has a modified cilium - cnidocil, and is armed with a stinging structure called a nematocyst. • Some nematocysts function to entangle the prey; others harpoon prey and inject a paralyzing toxin.

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

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

  8. Nervous System • Nerve Net- Cnidarians do not have a brain but they have simple sensory receptors that detect & respond to stimuli

  9. Circulation • NONE!!

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

  11. Reproduction • Asexual – budding- formation of outgrowths that pinch off from parent to live independently • Sexual- forms a zygote and free swimming planula that settles on ocean floor • *MOST ALTERNATE B/W POLP & MESDUSA LIFE FORM

  12. Reproduction (cont.)

  13. Reproduction (cont.)

  14. Excretion • mouth/anus- release waste